Applied Sciences

2024

Jump to: 2023, 2022, 2021, 2020, 2019

18 pages, 9202 KiB

Open AccessArticle

Propagation, Scattering and Defect Detection in a Circular Edge with Quasi-Edge Waves

by Peifeng Liang, Andrei Kotousov and Ching Tai Ng

Appl. Sci. 2024, 14(22), 10672; https://doi.org/10.3390/app142210672 - 19 Nov 2024

Viewed by 139

Abstract

Structural components with curved edges are common in many engineering designs. Fatigue cracks, corrosion and other types of defects and mechanical damage often initiate from (or are located close to) edges. Damage and defect detection in the presence of complex geometry represents a [...] Read more.

Structural components with curved edges are common in many engineering designs. Fatigue cracks, corrosion and other types of defects and mechanical damage often initiate from (or are located close to) edges. Damage and defect detection in the presence of complex geometry represents a significant challenge for non-destructive testing (NDT). To address this challenge, this paper investigates the fundamental mode of the quasi-symmetric edge-guided wave (

{Q E S}_{0}

) propagating along a curved edge, as well as its scattering characteristics in the presence of different types of edge defects. The finite element (FE) approach is used to investigate the propagation and mode shapes of the

{Q E S}_{0}

. It was found that the wave attenuation dramatically increases when the radius-to-thickness ratio is less than 20. Moreover, the mode shapes are significantly affected by the waveguide curvature as well as the excitation frequency. Additionally, to evaluate the sensitivity of

{Q E S}_{0}

to edge defects, different sizes of edge defects were investigated with the FE model, which validated against experimental results. The validated FE model was further employed to quantify the dependence of the amplitude of scattered waves for different types of edge defects. These studies indicate that the amplitude of scattered wave is very sensitive to the presence of edge defects. The main outcome of this work is the demonstrated ability of the

{Q E S}_{0}

wave mode to propagate over long distances and a high sensitivity of this mode to different types of edge defects, which manifest its great potential for detecting and characterising damage near the curved edges of structural components. Full article

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19 pages, 7133 KiB

Open AccessArticle

Fatigue Crack Growth Monitoring and Investigation on G20Mn5QT Cast Steel and Welds via Acoustic Emission

by Qingyang Liu, Zhenli Zhang, Giuseppe Lacidogna, Yantao Xu and Jie Xu

Appl. Sci. 2024, 14(20), 9612; https://doi.org/10.3390/app14209612 - 21 Oct 2024

Viewed by 681

Abstract

The fatigue crack growth properties of G20Mn5QT cast steel and corresponding butt welds, using compact tension specimens, were monitored and investigated via acoustic emission (AE) techniques. Fatigue crack growth is a combination of cyclic plastic deformations before the crack tip, tensile crack fractures, [...] Read more.

The fatigue crack growth properties of G20Mn5QT cast steel and corresponding butt welds, using compact tension specimens, were monitored and investigated via acoustic emission (AE) techniques. Fatigue crack growth is a combination of cyclic plastic deformations before the crack tip, tensile crack fractures, and shear crack fractures. The cyclic plastic deformations release the maximum amount of energy, which accounts for half of the total energy, and the second-largest number of AE signals, which are of the continuous-wave type. The tensile crack fractures release the second-largest amount of energy and the largest number of AE signals, which are of the burst-wave type. The shear crack fractures release the least amount of energy and the lowest number of AE signals, which are similar to the burst type, albeit with a relatively longer rise time and duration. Crack tip advancement can be regarded as a discontinuous process. The critical area before the crack tip brittlely ruptures when the fatigue damage caused by cyclic plastic deformations reaches critical status. The ruptures produce a large number of tensile crack fractures and rare shear crack fractures. Through fractography observation, the shear crack fractures occur probabilistically around defects caused by casting or welding, which lead to stress and strain in the local complex. Full article

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29 pages, 15583 KiB

Open AccessArticle

Advanced Structural Monitoring Technologies in Assessing the Performance of Retrofitted Reinforced Concrete Elements

by Maria C. Naoum, Nikos A. Papadopoulos, George M. Sapidis and Constantin E. Chalioris

Appl. Sci. 2024, 14(20), 9282; https://doi.org/10.3390/app14209282 - 12 Oct 2024

Viewed by 757

Abstract

Climate change induces extreme effects with lower-than-designed restoration periods, imposing the necessity of strengthening the structural integrity of existing and mainly older RC structures, which are often demonstrated to be under-reinforced in terms of the shear capacity, mainly due to outdated and old [...] Read more.

Climate change induces extreme effects with lower-than-designed restoration periods, imposing the necessity of strengthening the structural integrity of existing and mainly older RC structures, which are often demonstrated to be under-reinforced in terms of the shear capacity, mainly due to outdated and old design codes/standards. Thus, finding cost-effective and feasible methods to strengthen RC elements is becoming increasingly important. Thin RC layers for jacketing represent a modern advancement in repairing and retrofitting RC members. In this context, U-shaped mortar jackets were employed to strengthen three shear-critical beams. In addition, a critical aspect in the success of any jacketing method is the degree of bonding and interaction between the original member and the new jacket. Additionally, the performance of these U-shaped jackets was assessed using an Electro-Mechanical-Impedance-based (EMI-based) method using a Piezoelectric-Transducer-enabled (PZT-enabled) technique. The integration of advanced monitoring technologies in retrofitting applications offers valuable insights into the performance and longevity of the retrofit system. Therefore, this study aims to experimentally investigate the cohesion between construction materials and assess the effectiveness of U-shaped jackets. Through the proposed Structural Health Monitoring (SHM) technique, any degradation at the interface or slippage of the retrofitting jacket can be promptly detected, restraining further damage development and potential failure of the structure. Full article

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2023

Jump to: 2024, 2022, 2021, 2020, 2019

27 pages, 6391 KiB

Open AccessArticle

A Moment-Fitted Extended Spectral Cell Method for Structural Health Monitoring Applications

by Sergio Nicoli, Konstantinos Agathos, Pawel Kudela and Eleni Chatzi

Appl. Sci. 2023, 13(18), 10367; https://doi.org/10.3390/app131810367 - 16 Sep 2023

Cited by 5 | Viewed by 1286

Abstract

The spectral cell method has been shown as an efficient tool for performing dynamic analyses over complex domains. Its good performance can be attributed to the combination of the spectral element method with mesh-independent geometrical descriptions and the adoption of customized mass lumping [...] Read more.

The spectral cell method has been shown as an efficient tool for performing dynamic analyses over complex domains. Its good performance can be attributed to the combination of the spectral element method with mesh-independent geometrical descriptions and the adoption of customized mass lumping procedures for elements intersected by a boundary, which enable it to exploit highly efficient, explicit solvers. In this contribution, we introduce the use of partition-of-unity enrichment functions, so that additional domain features, such as cracks or material interfaces, can be seamlessly added to the modeling process. By virtue of the optimal lumping paradigm, explicit time integration algorithms can be readily applied to the non-enriched portion of a domain, which allows one to maintain fast computing simulations. However, the handling of enriched elements remains an open issue, particularly with respect to stability and accuracy concerns. In addressing this, we propose a novel mass lumping method for enriched spectral elements in the form of a customized moment-fitting procedure and study its accuracy and stability. While the moment-fitting equations are deployed in an effort to minimize the lumping error, stability issues are alleviated by deploying a leap-frog algorithm for the solution of the equations of motion. This approach is numerically benchmarked in the 2D and 3D modeling of damaged aluminium components and validated in comparison with experimental scanning laser Doppler vibrometer data of a composite panel under piezo-electric excitation. Full article

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12 pages, 2847 KiB

Open AccessArticle

Spectrum-Based Logistic Regression Modeling for the Sea Bottom Soil Categorization

by Uri Kushnir and Vladimir Frid

Appl. Sci. 2023, 13(14), 8131; https://doi.org/10.3390/app13148131 - 12 Jul 2023

Cited by 1 | Viewed by 818

Abstract

The present analysis of state of the art portrays that actual time series or spectrum backscattered data from a point on the sea bottom are rarely used as features for machine learning models. The paper deals with the artificial intelligence techniques used to [...] Read more.

The present analysis of state of the art portrays that actual time series or spectrum backscattered data from a point on the sea bottom are rarely used as features for machine learning models. The paper deals with the artificial intelligence techniques used to examine CHIRP-recorded data. The data were collected using a CHIRP sub-bottom profiler to study two sand bottom sites and two sandstone bottom sites in the offshore zone of Ashqelon City (Southern Israel). The first reflection time series and spectra of all the traces from the four sites generated two training and two test sets. Two logistic regression models were trained using the training sets and evaluated for accuracy using the test sets. The examination results indicate that types of sea bottom can be quantitatively characterized by applying logistic regression models to either the backscatter time series of a frequency-modulated signal or the spectrum of that backscatter. The examination accuracy reached 90% for the time series and 94% for the spectra. The application of spectral data as features for more advanced machine learning algorithms and the advantages of their combination with other types of data have great potential for future research and the enhancement of remote marine soil classification. Full article

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11 pages, 2446 KiB

Open AccessArticle

Multiclass Anomaly Detection of Bridge Monitoring Data with Data Migration between Different Bridges for Balancing Data

by Chunxu Qu, Hongming Zhang, Rui Zhang, Shuang Zou, Lihua Huang and Hongnan Li

Appl. Sci. 2023, 13(13), 7635; https://doi.org/10.3390/app13137635 - 28 Jun 2023

Cited by 3 | Viewed by 1299

Abstract

Structural health inspection systems are widely used to manage and maintain infrastructure that involves massive sensor devices. However, these sensors receive the natural environment or external factors in the long-term exposure to the outdoor environment, resulting in the failure of the sensors, which [...] Read more.

Structural health inspection systems are widely used to manage and maintain infrastructure that involves massive sensor devices. However, these sensors receive the natural environment or external factors in the long-term exposure to the outdoor environment, resulting in the failure of the sensors, which causes multiple categories of abnormal data in the collected data. The data often is unbalanced due to the random nature of failures. This unbalanced anomaly data poses a major challenge to existing anomaly detection methods and will affect the effectiveness of the information provided by the structural health monitoring system. In the paper, a data migration method is proposed to migrate bridge data to the target bridge dataset for expansion so that the number of images of different categories in the target bridge dataset increases. This method can be divided into three steps: firstly, to classify the data; secondly, to determine the suitability of the data and to construct the dataset; and finally, to train the data. The comparative validation is used to compare the training performance of the dataset using data migration with the dataset only using the target bridge to analyze the abnormal data identification in each category. In the experiment, the recall of some categories of data reached a significant increase of more than 30%, achieving better identification of various categories of abnormal data. Adopting the method of data migration between different bridges can solve the impact of imbalanced data and improve the recognition performance of categories with fewer images. Full article

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37 pages, 6325 KiB

Open AccessEditor’s ChoiceReview

Structural Health Monitoring and Management of Cultural Heritage Structures: A State-of-the-Art Review

by Michela Rossi and Dionysios Bournas

Appl. Sci. 2023, 13(11), 6450; https://doi.org/10.3390/app13116450 - 25 May 2023

Cited by 22 | Viewed by 4425

Abstract

In recent decades, the urgency to protect and upgrade cultural heritage structures (CHS) has become of primary importance due to their unique value and potential areas of impact (economic, social, cultural, and environmental). Structural health monitoring (SHM) and the management of CHS are [...] Read more.

In recent decades, the urgency to protect and upgrade cultural heritage structures (CHS) has become of primary importance due to their unique value and potential areas of impact (economic, social, cultural, and environmental). Structural health monitoring (SHM) and the management of CHS are emerging as decisive safeguard measures aimed at assessing the actual state of the conservation and integrity of the structure. Moreover, the data collected from SHM are essential to plan cost-effective and sustainable maintenance solutions, in compliance with the basic preservation principles for historic buildings, such as minimum intervention. It is evident that, compared to new buildings, the application of SHM to CHS is even more challenging because of the uniqueness of each monitored structure and the need to respect its architectural and historical value. This paper aims to present a state-of-the-art evaluation of the current traditional and innovative SHM techniques adopted for CHS and to identify future research trends. First, a general introduction regarding the use of monitoring strategies and technologies for CHS is presented. Next, various traditional SHM techniques currently used in CHS are described. Then, attention is focused on the most recent technologies, such as fibre optic sensors and smart-sensing materials. Finally, an overview of innovative methods and tools for managing and analysing SHM data, including IoT-SHM systems and the integration of BIM in heritage structures, is provided. Full article

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21 pages, 9165 KiB

Open AccessArticle

Preliminary Flutter Stability Assessment of the Double-Deck George Washington Bridge

by Sebastiano Russo, Gianfranco Piana, Luca Patruno and Alberto Carpinteri

Appl. Sci. 2023, 13(11), 6389; https://doi.org/10.3390/app13116389 - 23 May 2023

Cited by 1 | Viewed by 1508

Abstract

We deal with the flutter analysis of the George Washington bridge, in both the single- and double-deck configurations of 1931 and 1962, respectively. The influence of the additional lower deck on the aerodynamic behavior is investigated. To overcome the lack of aerodynamic data, [...] Read more.

We deal with the flutter analysis of the George Washington bridge, in both the single- and double-deck configurations of 1931 and 1962, respectively. The influence of the additional lower deck on the aerodynamic behavior is investigated. To overcome the lack of aerodynamic data, a simplified approach is followed based on Fung’s formulation, in which the flutter derivatives are expressed in terms of the real and imaginary parts of the Theodorsen function and of the steady-state aerodynamic coefficients of the deck cross-section. The latter are obtained by Computational Fluid Dynamics simulations conducted in ANSYS FLUENT, whereas the ANSYS Mechanical APDL finite element package is used to perform the flutter analyses. Two different methods for the application of the aeroelastic forces are employed for the double-deck configuration: (i) self-excited forces, based on flutter derivatives related to the whole cross-section, acting on the upper deck; and (ii) self-excited forces, based on flutter derivatives related to the single deck, simultaneously applied to the upper and lower decks. The obtained results are critically compared with theoretical predictions of simple formulas available from the literature; it is suggested that laboratory tests are needed since no experimental results seem to be available. Full article

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12 pages, 2297 KiB

Open AccessArticle

Final Setting Judgment and Safety Evaluation of Mass Concrete Based on Strain Monitoring

by Jie Xu, Chongyang Liu, Ziming Lu and Qian Ma

Appl. Sci. 2023, 13(4), 2283; https://doi.org/10.3390/app13042283 - 10 Feb 2023

Cited by 1 | Viewed by 1190

Abstract

A judgment method of the final setting time of mass concrete based on strain monitoring and the selection criterion of the starting point of effective deformation are proposed, and the safety of the concrete structure is evaluated based on this. Firstly, the strain [...] Read more.

A judgment method of the final setting time of mass concrete based on strain monitoring and the selection criterion of the starting point of effective deformation are proposed, and the safety of the concrete structure is evaluated based on this. Firstly, the strain monitoring theory of mass concrete is analyzed to clarify the temperature effect component and monitoring mechanism of an early strain of concrete. Then, taking the mass concrete plate of an engineering project as the research object combined with the mechanical analysis, the early strain monitoring data are segmented, and the relationship between the strain response and the temperature in different stages is fitted based on robust regression, so as to explore the correlation between strain and temperature in each stage and better explain the setting process of the concrete structure. Finally, taking the final setting time as the starting point of the effective strain, the safety of the concrete structure is further evaluated. The results show that there is a clear linear relationship between the strain response and temperature, and a high negative correlation between strain and temperature after the final setting. The time point when the frequency modulus corresponding to the strain enters a steady change and decreases with the increase of temperature is taken as the final setting time, which conforms to the concrete condensation mechanism and the temperature effect of early strain monitoring. Full article

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2022

Jump to: 2024, 2023, 2021, 2020, 2019

25 pages, 6179 KiB

Open AccessArticle

Efficient Detection of Defective Parts with Acoustic Resonance Testing Using Synthetic Training Data

by Matthias Heinrich, Bernd Valeske and Ute Rabe

Appl. Sci. 2022, 12(15), 7648; https://doi.org/10.3390/app12157648 - 29 Jul 2022

Cited by 6 | Viewed by 2080

Abstract

Analyzing eigenfrequencies by acoustic resonance testing enables a fast screening of components regarding structural defects. The eigenfrequencies of each specific part depend on the general geometric and material properties, including tolerable part-to-part variations, as well as on possible structural flaws. Separating good parts [...] Read more.

Analyzing eigenfrequencies by acoustic resonance testing enables a fast screening of components regarding structural defects. The eigenfrequencies of each specific part depend on the general geometric and material properties, including tolerable part-to-part variations, as well as on possible structural flaws. Separating good parts from defective ones is not straightforward and each application-specific sorting algorithm is usually found from experimental training data. However, there are limitations and training data collection may be intricate. We worked on this challenge focusing on machine-made model parts varying slightly in geometry. The application objective was the eigenfrequency-based detection of parts featuring a through-hole test defect drilled into some of the parts and enlarged stepwise. The eigenfrequencies were measured concomitantly. Unlike the industry standard, our approach is based on synthetic training data created mainly by simulation techniques, which resulted in a principally satisfactory classification of the good and defective parts. However, the parts with small defects were not identified from the eigenfrequencies alone, due to overlaying geometric variations. In order to counteract such noise and to improve defect detection based on synthetic training data, the specific actual part geometry was used, in the sense of additional a priori information. A multimodal data evaluation model showed a clearly enhanced sorting power. Full article

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21 pages, 14809 KiB

Open AccessArticle

Nondestructive Surface Crack Detection of Laser-Repaired Components by Laser Scanning Thermography

by Chuanqing Geng, Wenxiong Shi, Zhanwei Liu, Huimin Xie and Wei He

Appl. Sci. 2022, 12(11), 5665; https://doi.org/10.3390/app12115665 - 2 Jun 2022

Cited by 9 | Viewed by 2518

Abstract

As a revolutionary new technique, laser-engineered net shaping (LENS) is a layer additive manufacturing process that enables accurate, rapid and automatic repair of industrial component damage. In the laser repair (LR) process or in service, surface cracks can appear, which have a detrimental [...] Read more.

As a revolutionary new technique, laser-engineered net shaping (LENS) is a layer additive manufacturing process that enables accurate, rapid and automatic repair of industrial component damage. In the laser repair (LR) process or in service, surface cracks can appear, which have a detrimental effect on the repair quality and the mechanical performance; therefore, the surface crack detection of repaired components has attracted much attention. Laser spot thermography is an important nondestructive testing method with the advantages of non-contact, full-field and high precision, which shows great potential in the crack detection of repaired components. The selection of thermographic process parameters and the optimization of thermal image processing algorithms are key to the success of the nondestructive detection. In this paper, the influence of material properties and thermographic process parameters on the surface temperature gradient is studied based on the simulation of laser spot thermal excitation, and the selection windows of thermographic process parameters for iron-based and nickel-based alloys are obtained, which is applied to the surface crack detection of repaired components. To improve the computational efficiency of thermal images, the Prewitt edge detection algorithm is used in the thermal image processing, which realized fast extraction of cracks with a high signal-to-noise ratio (SNR), and the detection sensitivity of crack width can reach 10 μm. To further study the influence of surface roughness on the thermographic detection, repair layers with and without polishing process are characterized, which show that the Prewitt edge detection algorithm is well applicable to crack detection on surfaces with different roughness level. Full article

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19 pages, 4908 KiB

Open AccessArticle

A Novel Framework for Online Remaining Useful Life Prediction of an Industrial Slurry Pump

by Muhammad Mohsin Khan, Peter W. Tse and Jinzhao Yang

Appl. Sci. 2022, 12(10), 4839; https://doi.org/10.3390/app12104839 - 10 May 2022

Viewed by 1885

Abstract

An efficient Remaining Useful Life (RUL) prediction method is one of the most important features of a condition-based maintenance system. A running machine’s RUL prognosis in its real-time is a challenging task, especially when there is no historic failure data available [...] Read more.

An efficient Remaining Useful Life (RUL) prediction method is one of the most important features of a condition-based maintenance system. A running machine’s RUL prognosis in its real-time is a challenging task, especially when there is no historic failure data available for that particular machine. In this paper, an online RUL of an in-operation industrial slurry pump having no historical failure data has been predicted. At first, the available raw vibration datasets were filtered out for valid datasets. The obtained valid datasets were utilized for constructing the Health Degradation Trends (HDTs) using principal component analysis and a moving average method. Then, a novel procedure for automatically selecting the HDT’s data points for initiating the iteration process of prediction was formulated. Afterward, a hybrid deep LSTM model embedded with a smart learning rate mechanism was developed for estimating the online RUL using the selected points of HDTs. The online RUL prediction results produced by the developed model were quite satisfactory when they were compared with other online RUL prediction methods. Full article

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20 pages, 2230 KiB

Open AccessArticle

Investigations into the Recognisability of Gear Damage Sizes in Vibration Signals and Calculation of Appropriate Digital Filter Limits

by Andreas Beering and Karl-Ludwig Krieger

Appl. Sci. 2022, 12(9), 4216; https://doi.org/10.3390/app12094216 - 21 Apr 2022

Viewed by 1450

Abstract

The present work investigates the size of gear damage required for significant recognisable change in the vibration signal and presents a method to determine digital filter limits in order to emphasise the vibration behaviour in the time domain. For this purpose, two gears [...] Read more.

The present work investigates the size of gear damage required for significant recognisable change in the vibration signal and presents a method to determine digital filter limits in order to emphasise the vibration behaviour in the time domain. For this purpose, two gears are artificially damaged to four different degrees. The damage levels are determined by a tactile gear measurement and the gears are inserted into two intact gearboxes. Measurements at different speeds are used to generate a representative dataset. On the one hand, the recorded signals are examined via cross-correlation in the time domain. On the other hand, the occurring frequency components are examined using a windowed fast Fourier transformation. Based on the two observations, a statement is made about the recognisability of the damage levels of the two gears in the vibration signal. Furthermore, smoothed spectra are calculated via linear prediction coefficients (LPC) and an appropriate number of required coefficients is estimated via the Akaike information criterion. Subsequently, the calculated prediction coefficients are used as coefficients of an all-pole filter to calculate difference spectra. Based on the difference spectra, filter limits for a digital filter are derived to emphasise the damaged tooth meshing in the time domain. Full article

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15 pages, 6926 KiB

Open AccessArticle

Diagnosis of Artificial Flaws from Eddy Current Testing Signals Based on Sweep Frequency Non-Destructive Evaluation

by Filip Vaverka, Milan Smetana, Daniela Gombarska and Ladislav Janousek

Appl. Sci. 2022, 12(8), 3732; https://doi.org/10.3390/app12083732 - 7 Apr 2022

Cited by 3 | Viewed by 1778

Abstract

An investigation of artificial flaws in electromagnetic non-destructive evaluation using eddy-current frequency-response analysis is carried out in this study. A new approach incorporating innovative solution is proposed. The goal was to increase the resolution of gained signals in contrast to the conventional sweep-frequency [...] Read more.

An investigation of artificial flaws in electromagnetic non-destructive evaluation using eddy-current frequency-response analysis is carried out in this study. A new approach incorporating innovative solution is proposed. The goal was to increase the resolution of gained signals in contrast to the conventional sweep-frequency method. The proposed procedure was tested on real material specimens where differential responses were gained from artificial electro-discharge machined flaws. Two plate specimens having EDM flaws of various dimensions were inspected. Eddy-current responses due to the material flaws were sensed and compared to a dataset that was obtained by numerical modelling. The presented unique results clearly show that the resolution of a fixed probe driven with sweep-frequency excitation signal can be increased when the appropriate probe instrumentation is used and the characteristics are further mathematically processed. Full article

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13 pages, 4680 KiB

Open AccessArticle

Phase Reversal Method for Damage Imaging in Composite Laminates Based on Data Fusion

by Wei Han, Kan Feng and Huagen Yang

Appl. Sci. 2022, 12(6), 2894; https://doi.org/10.3390/app12062894 - 11 Mar 2022

Cited by 4 | Viewed by 2125

Abstract

This paper proposes a phase-reversal method (PRM) for damage imaging in plate structures. The PRM is a novel Lamb-wave-based method that mainly focuses on phase spectrum information of scattering waves reflected from a defect. The PRM reverses the phase angle along the propagation [...] Read more.

This paper proposes a phase-reversal method (PRM) for damage imaging in plate structures. The PRM is a novel Lamb-wave-based method that mainly focuses on phase spectrum information of scattering waves reflected from a defect. The PRM reverses the phase angle along the propagation path by using the inverse Fourier transform first, and then the reversal reconstruction of the wave field in the frequency domain is performed for damage imaging. The proposed method analyzes the scattered wave field without using the baseline data and structural parameters. Moreover, dispersion characteristics and anisotropy are not involved in the process of damage positioning, thus making the PRM suitable for damage monitoring of composite laminates. To improve the PRM accuracy further, a combined addition and multiplication method of the correlation coefficient (CAMM) is proposed, which can reduce the effects of phase and noise artifacts and distortion. The results of the finite element simulations and experiments show that the combination of the PRM and CAMM methods can accurately locate damage in composite structures. Therefore, the PRM and CAMM methods have great application potential in damage imaging in composite laminates. Full article

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9 pages, 1556 KiB

Open AccessArticle

Investigation of the Influence of Neutron Irradiation on Cladded Nuclear Reactor Pressure Vessel Steel Blocks by Magnetic Adaptive Testing

by Gábor Vértesy, Antal Gasparics, Ildikó Szenthe and Inge Uytdenhouwen

Appl. Sci. 2022, 12(4), 2074; https://doi.org/10.3390/app12042074 - 16 Feb 2022

Cited by 4 | Viewed by 1911

Abstract

The influence of neutron irradiation degradation on reactor pressure vessel steel was investigated. Large blocks were irradiated by neutrons in the BR2 reactor at a low irradiation temperature. They were measured by a nondestructive magnetic method, magnetic adaptive testing, before and after the [...] Read more.

The influence of neutron irradiation degradation on reactor pressure vessel steel was investigated. Large blocks were irradiated by neutrons in the BR2 reactor at a low irradiation temperature. They were measured by a nondestructive magnetic method, magnetic adaptive testing, before and after the neutron irradiation. It was shown that the modification of the magnetic parameters due to the neutron irradiation was well detectable by this nondestructive method. It was also shown that the influence of neutron irradiation could be detected with a reasonable signal-to-noise ratio through the cladding. The present results are considered as a first step towards the application of magnetic adaptive testing in the nuclear industry. Full article

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2021

Jump to: 2024, 2023, 2022, 2020, 2019

15 pages, 5014 KiB

Open AccessArticle

Research on Residual Life Estimation Method for KMN Steel Based on Nonlinear Ultrasonic Testing

by Pengfei Wang, Weiqiang Wang, Sanlong Zheng and Zengliang Gao

Appl. Sci. 2021, 11(23), 11385; https://doi.org/10.3390/app112311385 - 1 Dec 2021

Cited by 1 | Viewed by 1414

Abstract

The testing of KMN steel bending fatigue with different cycles was carried out using a nonlinear ultrasonic detector to obtain its nonlinear coefficient. The experimental results show that the nonlinear coefficient first increases and then decreases with an increase in fatigue cycles. The [...] Read more.

The testing of KMN steel bending fatigue with different cycles was carried out using a nonlinear ultrasonic detector to obtain its nonlinear coefficient. The experimental results show that the nonlinear coefficient first increases and then decreases with an increase in fatigue cycles. The relationship between the propagation of the micro-cracks inside the material and the nonlinear coefficient was researched by microscopic analysis in the dangerous position of the specimens. As the fatigue cycles increase, the microstructure of the specimen gradually deteriorates and cracks occur, which proves that nonlinear ultrasonic detection can be used to characterize the initiation of micro-cracks in the early fatigue stages of the material and that the nonlinear coefficient β of the material can be used to reflect the fatigue damage degree and fatigue life of the interior of the material. An analysis of the numerical statistics of the fatigue cracks inside the specimens was carried out, and the extreme value of fatigue cracks was calculated using the Gumbel distribution. An empirical formula for the nonlinear coefficient and crack growth size of KMN steel was established and then a method for estimating the fatigue life of KMN steel based on nonlinear ultrasonic testing was proposed. Full article

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13 pages, 16689 KiB

Open AccessArticle

Experimental Measurement of Residual Stress Distribution in Rail Specimens Using Ultrasonic L_CR Waves

by Young-In Hwang, Geonwoo Kim, Yong-Il Kim, Jeong-Hak Park, Man Yong Choi and Ki-Bok Kim

Appl. Sci. 2021, 11(19), 9306; https://doi.org/10.3390/app11199306 - 7 Oct 2021

Cited by 11 | Viewed by 3262

Abstract

Longitudinal critically refracted (L_CR) waves are considered bulk longitudinal waves and penetrate into an effective depth beneath the surface parallel to the material surface. Such L_CR waves can be employed to measure residual stresses because the acoustoelastic effect is the [...] Read more.

Longitudinal critically refracted (L_CR) waves are considered bulk longitudinal waves and penetrate into an effective depth beneath the surface parallel to the material surface. Such L_CR waves can be employed to measure residual stresses because the acoustoelastic effect is the basis for ultrasonic residual stress measurements. This effect is described by the relationship between change of wave travel time and stress applied when such waves propagate in a stressed medium. In this paper, stresses applied in a rail were evaluated by using a developed L_CR probe. With this transducer, it was verified how the difference in the arrival times of the L_CR waves showed a trend as the tensile stresses increased. The acoustoelastic coefficients were calculated using the relationship between the stresses and the travel times, and the residual stresses of the used rails were measured using these coefficients. In addition, the difference in residual stress distribution according to the characteristics of the wheel-rail contact surface was analyzed from the obtained residual stress value. It was concluded that this non-destructive evaluation technique using L_CR waves could be employed for accurate stress measurement of rails because differences in stress applied to the rail can be detected. Full article

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14 pages, 3598 KiB

Open AccessArticle

Application of Digital Image Analysis to the Prediction of Chlorophyll Content in Astragalus Seeds

by Yanan Xu, Keling Tu, Ying Cheng, Haonan Hou, Hailu Cao, Xuehui Dong and Qun Sun

Appl. Sci. 2021, 11(18), 8744; https://doi.org/10.3390/app11188744 - 19 Sep 2021

Cited by 4 | Viewed by 2567

Abstract

Chlorophyll fluorescence (CF) has been applied to measure the chlorophyll content of seeds, in order to determine seed maturity, but the high price of equipment limits its wider application. Astragalus seeds were used to explore the applicability of digital image analysis technology to [...] Read more.

Chlorophyll fluorescence (CF) has been applied to measure the chlorophyll content of seeds, in order to determine seed maturity, but the high price of equipment limits its wider application. Astragalus seeds were used to explore the applicability of digital image analysis technology to the prediction of seed chlorophyll content and to supply a low cost and alternative method. Our research comprised scanning and extracting the characteristic features of Astragalus seeds, determining the chlorophyll content, and establishing a predictive model of chlorophyll content in Astragalus seeds based on characteristic features. The results showed that the R² of the MLR prediction model established with multiple features was ≥0.947, and the R² of the MLP model was ≥0.943. By sorting of two single features, the R and G values, the R² reached 0.969 and 0.965, respectively. A germination result showed that the lower the chlorophyll content, the higher the quality of the seeds. Therefore, we draw a conclusion that digital image analysis technology can be used to predict effectively the chlorophyll content of Astragalus seeds, and provide a reference for the selection of mature and viable Astragalus seeds. Full article

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17 pages, 3439 KiB

Open AccessArticle

Strategies for Extracting Damage Induced AE Signals from Different Type Noise-Like Backgrounds for Carbon-Fibre Reinforced Polymers

by Ivan Panteleev, Aleksander Prokhorov and Oleg Plekhov

Appl. Sci. 2021, 11(16), 7506; https://doi.org/10.3390/app11167506 - 16 Aug 2021

Cited by 2 | Viewed by 1509

Abstract

This paper presents an algorithm for isolating a useful acoustic signal (corresponding to damage accumulation) against the background of a signal used to model the performance of an industrial rotary equipment. Acoustic emission signals induced by deformation and fracture were studied using a [...] Read more.

This paper presents an algorithm for isolating a useful acoustic signal (corresponding to damage accumulation) against the background of a signal used to model the performance of an industrial rotary equipment. Acoustic emission signals induced by deformation and fracture were studied using a uniaxial tensile test on woven laminate samples cut along the fiber and weft directions. The background signal is a random composition of acoustic pulses used to model the performance of an industrial rotary equipment. A comparison of useful and noise signals enables us to develop two algorithms based on frequency filtering of a signal and its decomposition into empirical modes. These algorithms can be used to isolate useful AE pulses against the background of all signal intensities under consideration. Full article

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19 pages, 15057 KiB

Open AccessFeature PaperArticle

Investigating the Micro/Macro-Texture Performance of Roller-Compacted Concrete Pavement under Simulated Traffic Abrasion

by Mostafa Adresi and Giuseppe Lacidogna

Appl. Sci. 2021, 11(12), 5704; https://doi.org/10.3390/app11125704 - 19 Jun 2021

Cited by 13 | Viewed by 2389

Abstract

Since the roller-compacted concrete pavement (RCCP) is almost smooth due to roller vibrations in the construction process, the lack of macro-texture prevents it from being used as a final surface. This study has made efforts to improve the RCCP by proposing different scenarios [...] Read more.

Since the roller-compacted concrete pavement (RCCP) is almost smooth due to roller vibrations in the construction process, the lack of macro-texture prevents it from being used as a final surface. This study has made efforts to improve the RCCP by proposing different scenarios to create new micro-/macro-texture surfaces and investigate their durability and skid resistance under traffic abrasion conditions. To prepare the micro-texture, eight RCCP specimens were cast using various 50–50% mixing proportions, and each of them alone in the form of siliceous and calcareous fine aggregates (natural and manufactured). For the macro-texture, each specimen was textured using such methods as seeding (three cases), stamping (two cases), and brooming (two cases). Since the durable texture should withstand the abrasive traffic flow, the RCCP-surface abrasion resistance was measured by the simulation method proposed in ASTM C944, and their skid resistance was evaluated by measuring the British pendulum test according to ASTM E303 before and after abrasion. The results showed that abrasion resistance of RCCP samples to changes in mixing design and skid resistance to changes in macro-texture have significant changes. In addition, different siliceous-calcareous sand combinations not only made the concrete mix more economical but also improved its performance in case of abrasion and skid resistance. The more was the manufactured sand proportion, the higher the fracture rate was and, hence, the abrasion resistance. Different macro-textures created on RCCP specimens generally showed acceptable skid resistance. In this regard, stamping had the highest mean texture depth (MTD) as well as BPN, and seeding had the lowest. Full article

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20 pages, 7714 KiB

Open AccessArticle

Validation of Selected Optical Methods for Assessing Polyethylene (PE) Liners Used in High Pressure Vessels for Hydrogen Storage

by Paweł Gąsior, Karol Wachtarczyk, Aleksander Błachut, Jerzy Kaleta, Neha Yadav, Marcin Ozga and Amelie Baron

Appl. Sci. 2021, 11(12), 5667; https://doi.org/10.3390/app11125667 - 18 Jun 2021

Cited by 15 | Viewed by 5061

Abstract

A polyethylene (PE) liner is the basic element in high-pressure type 4 composite vessels designed for hydrogen or compressed natural gas (CNG) storage systems. Liner defects may result in the elimination of the whole vessel from use, which is very expensive, both at [...] Read more.

A polyethylene (PE) liner is the basic element in high-pressure type 4 composite vessels designed for hydrogen or compressed natural gas (CNG) storage systems. Liner defects may result in the elimination of the whole vessel from use, which is very expensive, both at the manufacturing and exploitation stage. The goal is, therefore, the development of efficient non-destructive testing (NDT) methods to test a liner immediately after its manufacturing, before applying a composite reinforcement. It should be noted that the current regulations, codes and standards (RC&S) do not specify liner testing methods after manufacturing. It was considered especially important to find a way of locating and assessing the size of air bubbles and inclusions, and the field of deformations in liner walls. It was also expected that these methods would be easily applicable to mass-produced liners. The paper proposes the use of three optical methods, namely, visual inspection, digital image correlation (DIC), and optical fiber sensing based on Bragg gratings (FBG). Deformation measurements are validated with finite element analysis (FEA). The tested object was a prototype of a hydrogen liner for high-pressure storage (700 bar). The mentioned optical methods were used to identify defects and measure deformations. Full article

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21 pages, 12927 KiB

Open AccessArticle

Calibration of Acoustic Emission Parameters in Relation to the Equilibrium Moisture Content Variations in a Pinus sylvestris Beam

by Beatrice Bartolucci, Francesca Frasca, Anna Maria Siani and Chiara Bertolin

Appl. Sci. 2021, 11(11), 5236; https://doi.org/10.3390/app11115236 - 4 Jun 2021

Cited by 4 | Viewed by 2658

Abstract

Under constant temperature conditions, air relative humidity variations affect hygroscopic objects, such as wood, modifying their moisture content and provoking, at low values, damages and fractures. The parameters (amplitude, counts, and energy) derived from the acoustic emission non-destructive technique are calibrated with respect [...] Read more.

Under constant temperature conditions, air relative humidity variations affect hygroscopic objects, such as wood, modifying their moisture content and provoking, at low values, damages and fractures. The parameters (amplitude, counts, and energy) derived from the acoustic emission non-destructive technique are calibrated with respect to equilibrium moisture content values using 14 samplings of Pinus sylvestris. The experimental procedure uses multi-technique approaches involving a universal testing machine, digital image correlation, and acoustic emissions, and notes that the three parameters of acoustic emission strictly depend on the equilibrium moisture content. For a better interpretation, a statistical approach is applied to model the equilibrium moisture content variations radially and longitudinally. Amplitude, counts, and energy are calibrated as a function of the equilibrium moisture content, indicating that all three parameters are necessary to have an integral vision of the conservation of a wooden material. Moreover, the shape of the macro-fractures that occur at the surface can be associated with the level of moisture or dryness of the sample. Finally, the proposed method can be used in situ because, through acoustic emission monitoring, it is possible to quantify the fingerprint of the state of conservation of a material. Full article

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15 pages, 4392 KiB

Open AccessArticle

A Novel Life Prediction Model Based on Monitoring Electrical Properties of Self-Sensing Cement-Based Materials

by Mostafa Adresi, Jean-Marc Tulliani, Giuseppe Lacidogna and Paola Antonaci

Appl. Sci. 2021, 11(11), 5080; https://doi.org/10.3390/app11115080 - 30 May 2021

Cited by 10 | Viewed by 3024

Abstract

Assessing the damage level in concrete infrastructures over time is a critical issue to plan their timely maintenance with proper actions. Self-sensing concretes offer new opportunities for damage assessment by monitoring their electrical properties and relating their variations to damage levels. In this [...] Read more.

Assessing the damage level in concrete infrastructures over time is a critical issue to plan their timely maintenance with proper actions. Self-sensing concretes offer new opportunities for damage assessment by monitoring their electrical properties and relating their variations to damage levels. In this research, fatigue tests were conducted to study the response of a self-sensing concrete under high-cycle dynamic loading. The concept of G-value was defined as the slope of the voltage response baseline of the self-sensing concrete over time that reflects the damage created under the fatigue-loading test. Based on this definition, log (G)–log (N) curves were obtained using a linear regression approach, with N representing the number of cycles during the fatigue tests. While traditional fatigue curves S-log (N) are used to estimate the remaining life under fatigue loading, log (G)–log (N) diagrams can be used to determine the damage level based on the voltage response of the self-sensing concrete as a function of the loading history. This finding can be useful for the estimation of the lifetime and remaining life of self-sensing concrete structures and infrastructure, eventually helping to optimize the related maintenance operations. Full article

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16 pages, 4916 KiB

Open AccessArticle

Defining a Non-Destructive In Situ Approach for the Determination of Historical Mortar Strength Using the Equotip Hardness Tester

by Elisa Mammoliti, Antonio Ferretti, Michele Malavolta, Riccardo Teloni, Paolo Ruggeri and Graziella Roselli

Appl. Sci. 2021, 11(11), 4788; https://doi.org/10.3390/app11114788 - 23 May 2021

Cited by 6 | Viewed by 3360

Abstract

The determination of mechanical parameters of historical mortars is a crucial aspect in the analysis of masonry in ancient buildings, especially for evaluating their quality and planning the appropriate restoration interventions. Due to conservation reasons, creating a comprehensive database is generally not possible [...] Read more.

The determination of mechanical parameters of historical mortars is a crucial aspect in the analysis of masonry in ancient buildings, especially for evaluating their quality and planning the appropriate restoration interventions. Due to conservation reasons, creating a comprehensive database is generally not possible because cutting out masonry specimens relates to damaging historical structures. This study starts with the need to characterize the mortar quality of different buildings in the town of Camerino (Central Italy) which has been strongly damaged by the 2016–2017 seismic sequence. A non-destructive collecting data strategy based on the use of the Equotip hardness tester (EQ) has been set up by evaluating the most appropriates impact strategy (single or repeated) and the range of measurements to calculate the basic statistics. The seismic damage suffered by the buildings allowed the rare opportunity to take samples from several walls and carry out laboratory tests to determine their Uniaxial Compressive Strength (UCS). The comparison between the results of the two types of tests made it possible to calibrate a relationship between the EQ values and the UCS. The Pearson’s coefficient of determination derived from an exponential interpolation (R₂ = 0.81) confirmed a strong relationship between the EQ values derived from the tests on the specimens and the UCS. Moreover, comparing the in situ EQ measurements with the ones performed on the specimens prepared for the compressive tests, a general underestimation of the in situ EQ values has been observed, possibly due to the presence of a superficial alteration layer of the exposed mortar. From these results, we propose a correction of the in situ measurements able to obtain a more appropriate strength estimate of the historical mortars. Full article

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15 pages, 3228 KiB

Open AccessArticle

Asymptotic Analytical Solution on Lamb Waves in Functionally Graded Nano Copper Layered Wafer

by Yifeng Hu, Xiaoshan Cao, Yi Niu, Yan Ru and Junping Shi

Appl. Sci. 2021, 11(10), 4442; https://doi.org/10.3390/app11104442 - 13 May 2021

Cited by 2 | Viewed by 1734

Abstract

In this study, the feasibility of using Lamb waves in functionally graded (FG) nano copper layered wafers in nondestructive evaluation is evaluated. The elastic parameters and mass densities of these wafers vary with thickness due to the variation in grain size. The power [...] Read more.

In this study, the feasibility of using Lamb waves in functionally graded (FG) nano copper layered wafers in nondestructive evaluation is evaluated. The elastic parameters and mass densities of these wafers vary with thickness due to the variation in grain size. The power series technique is used to solve the governing equations with variable coefficients. To analyze multilayered structures, of which the material parameters are continuous but underivable, a modified transfer matrix method is proposed and combined with the power series method. Results show that multiple modes of Lamb waves exist in FG nano copper wafers. Moreover, the gradient property leads to a decrease in phase velocity, and the absolute value of the phase velocity variation is positively correlated with the gradient coefficient. The phase velocity variation and variation rate in Mode 2 are smaller than those in other modes. The findings indicate that Mode 4 is recommended for nondestructive evaluation. However, if the number of layers is greater than four, the dispersion curves of the Lamb waves in the multilayer structures tend to coincide with those in the equivalent uniform structures. The results of this study provide theoretical guidance for the nondestructive evaluation of FG nanomaterial layered structures. Full article

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18 pages, 6722 KiB

Open AccessArticle

Characterising Modal Behaviour of a Cantilever Beam at Different Heating Rates for Isothermal Conditions

by Khangamlung Kamei, Muhammad A. Khan and Kamran A. Khan

Appl. Sci. 2021, 11(10), 4375; https://doi.org/10.3390/app11104375 - 12 May 2021

Cited by 9 | Viewed by 4877

Abstract

The effect of temperature on structural response is a concern in engineering applications. The literature has highlighted that applied temperature loads change the system vibration behaviour. However, there is limited information available about temperature impacting the dynamic response. This paper investigated the heating [...] Read more.

The effect of temperature on structural response is a concern in engineering applications. The literature has highlighted that applied temperature loads change the system vibration behaviour. However, there is limited information available about temperature impacting the dynamic response. This paper investigated the heating rates effects on modal parameters for both with crack and without crack conditions in a cantilever beam. A beam subjected to three heating rates was considered: 2, 5, and 8 °C/min. The first one was assumed as a slow heating rate while the others were assumed as moderate and high, respectively. This controlled rate of heating was achieved by using a proportional-integral-derivative (PID) temperature controller. The results showed that heating at different rates has little impact on modal parameters. While this effect is minimal at lower temperatures and more evident at higher temperatures. The results of temperature ramped at 2, 5, and 8 °C/min were compared with the numerical and analytical results only for all the isothermal conditions. It was observed that the beam natural frequency and its modal amplitude decrease with the increase in temperatures and crack depths. Therefore, it is concluded that the rate of heating can make a slight impact on the dynamics response of any mechanical system. Full article

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13 pages, 5672 KiB

Open AccessArticle

Measurements of the Magnetic Field Variations Related with the Size of V-Shaped Notches in Steel Pipes

by J. Jesús Villegas-Saucillo, José Javier Díaz-Carmona, Marco A. Escarola-Rosas, Héctor Vázquez-Leal, Jaime Martínez-Castillo and Agustín L. Herrera-May

Appl. Sci. 2021, 11(9), 3940; https://doi.org/10.3390/app11093940 - 27 Apr 2021

Cited by 5 | Viewed by 2199

Abstract

Gas and oil pipeline networks require periodic inspections to detect cracks or notches that can cause industrial accidents and environmental contamination. For these inspections, the metal magnetic memory (MMM) method could be used as a non-destructive testing (NDT) technique, which does not need [...] Read more.

Gas and oil pipeline networks require periodic inspections to detect cracks or notches that can cause industrial accidents and environmental contamination. For these inspections, the metal magnetic memory (MMM) method could be used as a non-destructive testing (NDT) technique, which does not need expensive equipment and high-skilled operators. However, more investigations are required to quantify the size and shape of defects in ferromagnetic pipes using the MMM signals. We present experimental measurements of MMM signals around five small V-shaped notches of an ASTM-A36 steel pipe using a three-axis magnetoresistive sensor. The V-shaped notches have different values of depth (500 µm, 1000 µm, 1500 µm, 2000 µm and 2500 µm) and width (1000 µm, 1500 µm, 2000 µm, 3000 µm and 3500 µm). We measured the variations of tangential and normal MMM signals around these defects and their relationships with the size of each defect. The first V-notch defect (500 μm depth and 1000 μm width) registers variations of the tangential and normal MMM signals of 14.32 μT ± 1.62 μT and 27.95 μT ± 1.14 μT, respectively. On the other hand, the fifth V-notch defect (2500 μm depth and 3500 μm width) has variations of the tangential and normal MMM signals of 68.75 μT ± 1.10 μT and 71.37 μT ± 0.72 μT, respectively. The MMM method could be used for real-time monitoring of V-shaped notches in steel pipes. This method does not require special treatment of steel pipes. Full article

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14 pages, 5839 KiB

Open AccessArticle

Validation of Fresnel–Kirchhoff Integral Method for the Study of Volume Dielectric Bodies

by Soumia Imane Taleb, Cristian Neipp, Jorge Francés, Andrés Márquez, Mariela L. Alvarez, Antonio Hernández, Sergi Gallego and Augusto Beléndez

Appl. Sci. 2021, 11(9), 3800; https://doi.org/10.3390/app11093800 - 22 Apr 2021

Cited by 1 | Viewed by 2445

Abstract

In this work, we test a nondestructive optical method based on the Fresnel–Kirchhoff integral, which could be applied to different fields of engineering, such as detection of small cracks in structures, determination of dimensions for small components, analysis of composition of materials, etc. [...] Read more.

In this work, we test a nondestructive optical method based on the Fresnel–Kirchhoff integral, which could be applied to different fields of engineering, such as detection of small cracks in structures, determination of dimensions for small components, analysis of composition of materials, etc. The basic idea is to apply the Fresnel–Kirchhoff integral method to the study of the properties of small-volume dielectric objects. In this work, we study the validity of this method. To do this, the results obtained by using this technique were compared to those obtained by rigorously solving the Helmholtz equation for a dielectric cylinder of circular cross-section. As an example of the precision of the method, the Fresnel–Kirchhoff integral method was applied to obtain the refractive index of a hair by fitting the theoretical curve to the experimental results of the diffraction pattern of the hair measured with a CCD camera. In a same manner, the method also was applied to obtain the dimensions of a crack artificially created in a piece of plastic. Full article

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10 pages, 1919 KiB

Open AccessArticle

Correlation between Uniaxial Compression Test and Ultrasonic Pulse Rate in Cement with Different Pozzolanic Additions

by Leticia Presa, Jorge L. Costafreda and Domingo Alfonso Martín

Appl. Sci. 2021, 11(9), 3747; https://doi.org/10.3390/app11093747 - 21 Apr 2021

Cited by 5 | Viewed by 2286

Abstract

This work aims to study the relationship between the compression resistance and velocity from ultrasonic pulses in samples of mortars with 25% of pozzolanic content. Pozzolanic cement is a low-priced sustainable material that can reduce costs and CO₂ emissions that are produced [...] Read more.

This work aims to study the relationship between the compression resistance and velocity from ultrasonic pulses in samples of mortars with 25% of pozzolanic content. Pozzolanic cement is a low-priced sustainable material that can reduce costs and CO₂ emissions that are produced in the manufacturing of cement from the calcination of calcium carbonate. Using ultrasonic pulse velocity (UPV) to estimate the compressive resistance of mortars with pozzolanic content reduces costs when evaluating the quality of structures built with this material since it is not required to perform an unconfined compression test. The objective of this study is to establish a correlation in order to estimate the compression resistance of this material from its ultrasonic pulse velocity. For this purpose, we studied a total of 16 cement samples, including those with additions of pozzolanic content with different compositions and a sample without any additions. The results obtained show the mentioned correlation, which establishes a basis for research with a higher number of samples to ascertain if it holds true at greater curing ages. Full article

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18 pages, 2693 KiB

Open AccessArticle

Dynamic Identification of Tensile Force in Tie-Rods by Interferometric Radar Measurements

by Domenico Camassa, Anna Castellano, Aguinaldo Fraddosio, Giuseppe Miglionico and Mario Daniele Piccioni

Appl. Sci. 2021, 11(8), 3687; https://doi.org/10.3390/app11083687 - 19 Apr 2021

Cited by 27 | Viewed by 2393

Abstract

An experimental investigation on the accuracy of dynamically determined tensile force in tie-rods by applying the interferometric radar technique was performed. Tie-rods were used in historical masonry constructions for absorbing thrusts of arches and vaults, and the radar interferometry may represent a fast [...] Read more.

An experimental investigation on the accuracy of dynamically determined tensile force in tie-rods by applying the interferometric radar technique was performed. Tie-rods were used in historical masonry constructions for absorbing thrusts of arches and vaults, and the radar interferometry may represent a fast and easy non-destructive approach for the tensile force identification in the occasion of structural assessments. Laboratory dynamic tests on a cable under a known tensile force show that, provided that a suitable dynamic identification model is used, tensile force evaluations made stating from interferometric radar measurements were characterized by a very good accuracy (mean error in the tensile force estimation less than 2%), comparable with evaluations made starting from accelerometric measurements. In particular, the dynamic identification model considered is a modified version of a model proposed in the literature. The influence on the accuracy in the determination of the tensile force of some features of the experimental setup, like, e.g., the employ of corner reflectors, is discussed. Full article

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11 pages, 2562 KiB

Open AccessArticle

Numerical Modeling of Nondestructive Testing of Various Conductive Objects inside Metal Enclosures Using ELF/VLF Magnetic Fields

by Hoyoung Kim and Vijay Harid

Appl. Sci. 2021, 11(8), 3665; https://doi.org/10.3390/app11083665 - 19 Apr 2021

Viewed by 1997

Abstract

Nondestructive evaluation of various conductive objects through metal enclosures is investigated by using ELF/VLF magnetic induction fields in detailed simulations. ELF/VLF magnetic fields (<30 kHz) have a unique ability to penetrate highly conductive or permeable shields. Using a magnetic dipole source antenna, objects [...] Read more.

Nondestructive evaluation of various conductive objects through metal enclosures is investigated by using ELF/VLF magnetic induction fields in detailed simulations. ELF/VLF magnetic fields (<30 kHz) have a unique ability to penetrate highly conductive or permeable shields. Using a magnetic dipole source antenna, objects hidden inside a metal enclosure are imaged via examining distortions to the field outside the enclosure. The field distortion is parametrically studied by varying the size, conductivity, and permeability of the hidden objects. Furthermore, the importance of the conductivity of the enclosure itself is investigated using both low (10⁶ S/m) and high (10⁸ S/m) conductivity metallic shields. It is shown that the responses are quite sensitive to the object and shield parameters; both qualitative and quantitative properties of the field distortions are described in detail. The simulation results suggest that properties of hidden conductive or permeable objects, over a relatively wide range of parameters (both geometry and material), can be inferred nondestructively using ELF/VLF magnetic induction fields. Full article

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13 pages, 3597 KiB

Open AccessArticle

Interpretation of Nondestructive Magnetic Measurements on Irradiated Reactor Steel Material

by Gábor Vértesy, Antal Gasparics, Ildikó Szenthe and Inge Uytdenhouwen

Appl. Sci. 2021, 11(8), 3650; https://doi.org/10.3390/app11083650 - 18 Apr 2021

Cited by 5 | Viewed by 1916

Abstract

Neutron irradiation-generated embrittlement of nuclear pressure vessel steel was inspected by a nondestructive magnetic method, called magnetic adaptive testing (MAT). This method is based on systematic measurement and evaluation of minor magnetic hysteresis loops. Result of MAT measurement was compared with the result [...] Read more.

Neutron irradiation-generated embrittlement of nuclear pressure vessel steel was inspected by a nondestructive magnetic method, called magnetic adaptive testing (MAT). This method is based on systematic measurement and evaluation of minor magnetic hysteresis loops. Result of MAT measurement was compared with the result of the traditional Charpy measurement. Good correlation was found between these parameters. One of the main findings of the present work is that the considerable part of scatter of points obtained by magnetic measurement can be attributed to local material inhomogeneity. Another important conclusion is that the embrittlement highly depends on the initial local material conditions, i.e., the initial microstructure, which are very different even within the same block of reactor steel material. By taking this into account, the magnetic descriptors obtain more precise determination of the local embrittlement than the traditionally used destructive mechanical parameters from Charpy data. Full article

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15 pages, 3890 KiB

Open AccessArticle

Structural Health Monitoring of Walking Dragline Excavator Using Acoustic Emission

by Vera Barat, Artem Marchenkov, Dmitry Kritskiy, Vladimir Bardakov, Marina Karpova, Mikhail Kuznetsov, Anastasia Zaprudnova, Sergey Ushanov and Sergey Elizarov

Appl. Sci. 2021, 11(8), 3420; https://doi.org/10.3390/app11083420 - 11 Apr 2021

Cited by 2 | Viewed by 4676

Abstract

The article is devoted to the organization of the structural health monitoring of a walking dragline excavator using the acoustic emission (AE) method. Since the dragline excavator under study is a large and noisy industrial facility, preliminary prospecting researches were carried out to [...] Read more.

The article is devoted to the organization of the structural health monitoring of a walking dragline excavator using the acoustic emission (AE) method. Since the dragline excavator under study is a large and noisy industrial facility, preliminary prospecting researches were carried out to conduct effective control by the AE method, including the study of AE sources, AE waveguide, and noise parameters analysis. In addition, AE filtering methods were improved. It is shown that application of the developed filtering algorithms allows to detect AE impulses from cracks and defects against a background noise exceeding the useful signal in amplitude and intensity. Using the proposed solutions in the monitoring of a real dragline excavator during its operation made it possible to identify a crack in one of its elements (weld joint in a dragline back leg). Full article

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22 pages, 3301 KiB

Open AccessArticle

High-Precision and Four-Dimensional Tracking System with Dual Receivers of Pipeline Inspection Gauge

by Yue Long, Songling Huang, Lisha Peng, Wenzhi Wang, Shen Wang and Wei Zhao

Appl. Sci. 2021, 11(8), 3366; https://doi.org/10.3390/app11083366 - 8 Apr 2021

Cited by 2 | Viewed by 2624

Abstract

Pipeline inspection gauges (PIGs) are widely used for nondestructive testing of oil and natural gas pipelines, while above ground markers (AGMs) can locate and track the PIG through a variety of methods, including magnetic flux leakage signals, acoustic signals, and extremely low-frequency (ELF) [...] Read more.

Pipeline inspection gauges (PIGs) are widely used for nondestructive testing of oil and natural gas pipelines, while above ground markers (AGMs) can locate and track the PIG through a variety of methods, including magnetic flux leakage signals, acoustic signals, and extremely low-frequency (ELF) magnetic signals. Traditional AGMs have the disadvantages of low positioning accuracy and only one-dimensional tracking capability. In this paper, a newly-designed PIG tracking system based on the ELF magnetic field is proposed by assembling dual receivers. Moreover, this paper develops a magnetic field sign-integration algorithm to achieve high-precision and four-dimensional (4-D) tracking of PIG. The simulation and experiment results demonstrate that the tracking system has the capability of 4-D tracking. In comparison with the previously published work, the designed tracking system improves the positioning accuracy and orientation tracking accuracy by more than 50%. The dual receivers tracking system also has the characteristic of high-robustness. Even in the state of lateral offset or tilt, it can still achieve accurate tracking of PIG. The realization of PIG’s high-precision 4-D tracking can improve the accuracy of defect location. Moreover, it can also provide the latest pipeline network layout and facilitate pipeline maintenance and pipeline surveying applications. Full article

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15 pages, 2938 KiB

Open AccessArticle

Nondestructive Contactless Monitoring of Damage in Joints between Composite Structural Components Incorporating Sensing Elements via 3D-Printing

by Dimitrios G. Dimogianopoulos and Dionysios E. Mouzakis

Appl. Sci. 2021, 11(7), 3230; https://doi.org/10.3390/app11073230 - 3 Apr 2021

Cited by 3 | Viewed by 2089

Abstract

A vibration-testing framework for detecting and identifying failing joints between composite structural members without dedicated equipment (accelerometers, amplifiers) or time-consuming system modeling methods is introduced. The sensing element is a 2826MB Metglas^® magnetoelastic strip embedded in one of the members during its [...] Read more.

A vibration-testing framework for detecting and identifying failing joints between composite structural members without dedicated equipment (accelerometers, amplifiers) or time-consuming system modeling methods is introduced. The sensing element is a 2826MB Metglas^® magnetoelastic strip embedded in one of the members during its 3D-printing (layer-by-layer) fabrication process in fused deposition modeling mode. External dynamic loading of the structure causes changes to the strip’s magnetization, thus inducing voltage to a nearby placed coil in a contactless manner. The resulting signal depends on the structure’s behavior under loading (and therefore its condition), and may be recorded without amplification or filtering by conventional oscilloscopes. Its frequency analysis reveals patterns of shifted frequency and/or altered damping at specific modes attributed to failing joints. Apart from yielding results using less dedicated equipment than other vibration-testing methods, the current framework offers two additional benefits: (i) Excitation may be applied to the same structural point for all monitored joints; (ii) estimation of damping values for a given mode does not have to rely on empirical or system modelling techniques (both requiring dedicated expertise). Test runs with structures formed by two or three composite slabs joined in-series indicate promising results with successful detection and identification of failing joints. Full article

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14 pages, 5084 KiB

Open AccessArticle

Monte-Carlo-Based Estimation of the X-ray Energy Spectrum for CT Artifact Reduction

by Ehsan Nazemi, Nathanaël Six, Domenico Iuso, Björn De Samber, Jan Sijbers and Jan De Beenhouwer

Appl. Sci. 2021, 11(7), 3145; https://doi.org/10.3390/app11073145 - 1 Apr 2021

Cited by 10 | Viewed by 4654

Abstract

Beam hardening and scattering effects can seriously degrade image quality in polychromatic X-ray CT imaging. In recent years, polychromatic image reconstruction techniques and scatter estimation using Monte Carlo simulation have been developed to compensate for beam hardening and scattering CT artifacts, respectively. Both [...] Read more.

Beam hardening and scattering effects can seriously degrade image quality in polychromatic X-ray CT imaging. In recent years, polychromatic image reconstruction techniques and scatter estimation using Monte Carlo simulation have been developed to compensate for beam hardening and scattering CT artifacts, respectively. Both techniques require knowledge of the X-ray tube energy spectrum. In this work, Monte Carlo simulations were used to calculate the X-ray energy spectrum of FleXCT, a novel prototype industrial micro-CT scanner, enabling beam hardening and scatter reduction for CT experiments. Both source and detector were completely modeled by Monte Carlo simulation. In order to validate the energy spectra obtained via Monte Carlo simulation, they were compared with energy spectra obtained via a second method. Here, energy spectra were calculated from empirical measurements using a step wedge sample, in combination with the Maximum Likelihood Expectation Maximization (MLEM) method. Good correlation was achieved between both approaches, confirming the correct modeling of the FleXCT system by Monte Carlo simulation. After validation of the modeled FleXCT system through comparing the X-ray spectra for different tube voltages inside the detector, we calculated the X-ray spectrum of the FleXCT X-ray tube, independent of the flat panel detector response, which is a prerequisite for beam hardening and scattering CT artifacts. Full article

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13 pages, 2232 KiB

Open AccessArticle

A Hybrid Hidden Markov Model for Pipeline Leakage Detection

by Mingchi Zhang, Xuemin Chen and Wei Li

Appl. Sci. 2021, 11(7), 3138; https://doi.org/10.3390/app11073138 - 1 Apr 2021

Cited by 8 | Viewed by 3137

Abstract

In this paper, a deep neural network hidden Markov model (DNN-HMM) is proposed to detect pipeline leakage location. A long pipeline is divided into several sections and the leakage occurs in different section that is defined as different state of hidden Markov model [...] Read more.

In this paper, a deep neural network hidden Markov model (DNN-HMM) is proposed to detect pipeline leakage location. A long pipeline is divided into several sections and the leakage occurs in different section that is defined as different state of hidden Markov model (HMM). The hybrid HMM, i.e., DNN-HMM, consists of a deep neural network (DNN) with multiple layers to exploit the non-linear data. The DNN is initialized by using a deep belief network (DBN). The DBN is a pre-trained model built by stacking top-down restricted Boltzmann machines (RBM) that compute the emission probabilities for the HMM instead of Gaussian mixture model (GMM). Two comparative studies based on different numbers of states using Gaussian mixture model-hidden Markov model (GMM-HMM) and DNN-HMM are performed. The accuracy of the testing performance between detected state sequence and actual state sequence is measured by micro

F_{1}

score. The micro

F_{1}

score approaches 0.94 for GMM-HMM method and it is close to 0.95 for DNN-HMM method when the pipeline is divided into three sections. In the experiment that divides the pipeline as five sections, the micro

F_{1}

score for GMM-HMM is 0.69, while it approaches 0.96 with DNN-HMM method. The results demonstrate that the DNN-HMM can learn a better model of non-linear data and achieve better performance compared to GMM-HMM method. Full article

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25 pages, 11408 KiB

Open AccessArticle

An Improved Hilbert–Huang Transform for Vibration-Based Damage Detection of Utility Timber Poles

by Ipshita Das, Mohammad Taufiqul Arif, Aman Maung Than Oo and Mahbube Subhani

Appl. Sci. 2021, 11(7), 2974; https://doi.org/10.3390/app11072974 - 26 Mar 2021

Cited by 11 | Viewed by 2605

Abstract

In this study, vibration based non-destructive testing (NDT) technique is adopted for assessing the condition of in-service timber pole. Timber is a natural material, and hence the captured broadband signal (induced from impact using modal hammer) is greatly affected by the uncertainty on [...] Read more.

In this study, vibration based non-destructive testing (NDT) technique is adopted for assessing the condition of in-service timber pole. Timber is a natural material, and hence the captured broadband signal (induced from impact using modal hammer) is greatly affected by the uncertainty on wood properties, structure, and environment. Therefore, advanced signal processing technique is essential in order to extract features associated with the health condition of timber poles. In this study, Hilbert–Huang Transform (HHT) and Wavelet Packet Transform (WPT) are implemented to conduct time-frequency analysis on the acquired signal related to three in-service poles and three unserviceable poles. Firstly, mother wavelet is selected for WPT using maximum energy to Shannon entropy ratio. Then, the raw signal is divided into different frequency bands using WPT, followed by reconstructing the signal using wavelet coefficients in the dominant frequency bands. The reconstructed signal is then further decomposed into mono-component signals by Empirical Mode Decomposition (EMD), known as Intrinsic Mode Function (IMF). Dominant IMFs are selected using correlation coefficient method and instantaneous frequencies of those dominant IMFs are generated using HHT. Finally, the anomalies in the instantaneous frequency plots are efficiently utilised to determine vital features related to pole condition. The results of the study showed that HHT with WPT as pre-processor has a great potential for the condition assessment of utility timber poles. Full article

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19 pages, 2283 KiB

Open AccessReview

Design of a Computed Tomography Automation Architecture

by Nicholas Hashem, Mitchell Pryor, Derek Haas and James Hunter

Appl. Sci. 2021, 11(6), 2858; https://doi.org/10.3390/app11062858 - 23 Mar 2021

Cited by 5 | Viewed by 5632

Abstract

This paper presents a literature review on techniques related to the computed tomography procedure that incorporate automation elements in their research investigations or industrial applications. Computed tomography (CT) is a non-destructive testing (NDT) technique in that the imaging and inspection are performed without [...] Read more.

This paper presents a literature review on techniques related to the computed tomography procedure that incorporate automation elements in their research investigations or industrial applications. Computed tomography (CT) is a non-destructive testing (NDT) technique in that the imaging and inspection are performed without damaging the sample, allowing for additional or repeated analysis if necessary. The reviewed literature is organized based on the steps associated with a general NDT task in order to define an end-to-end computed tomography automation architecture. The process steps include activities prior to image collection, during the scan, and after the data are collected. It further reviews efforts related to repeating this process based on a previous scan result. By analyzing the multiple existing but disparate efforts found in the literature, we present a framework for fully automating NDT procedures and discuss the remaining technical gaps in the developed framework. Full article

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28 pages, 4394 KiB

Open AccessReview

Recent Advancements in Non-Destructive Testing Techniques for Structural Health Monitoring

by Patryk Kot, Magomed Muradov, Michaela Gkantou, George S. Kamaris, Khalid Hashim and David Yeboah

Appl. Sci. 2021, 11(6), 2750; https://doi.org/10.3390/app11062750 - 18 Mar 2021

Cited by 143 | Viewed by 13431

Abstract

Structural health monitoring (SHM) is an important aspect of the assessment of various structures and infrastructure, which involves inspection, monitoring, and maintenance to support economics, quality of life and sustainability in civil engineering. Currently, research has been conducted in order to develop non-destructive [...] Read more.

Structural health monitoring (SHM) is an important aspect of the assessment of various structures and infrastructure, which involves inspection, monitoring, and maintenance to support economics, quality of life and sustainability in civil engineering. Currently, research has been conducted in order to develop non-destructive techniques for SHM to extend the lifespan of monitored structures. This paper will review and summarize the recent advancements in non-destructive testing techniques, namely, sweep frequency approach, ground penetrating radar, infrared technique, fiber optics sensors, camera-based methods, laser scanner techniques, acoustic emission and ultrasonic techniques. Although some of the techniques are widely and successfully utilized in civil engineering, there are still challenges that researchers are addressing. One of the common challenges within the techniques is interpretation, analysis and automation of obtained data, which requires highly skilled and specialized experts. Therefore, researchers are investigating and applying artificial intelligence, namely machine learning algorithms to address the challenges. In addition, researchers have combined multiple techniques in order to improve accuracy and acquire additional parameters to enhance the measurement processes. This study mainly focuses on the scope and recent advancements of the Non-destructive Testing (NDT) application for SHM of concrete, masonry, timber and steel structures. Full article

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17 pages, 8277 KiB

Open AccessArticle

Damage Evolution Analysis in a “Spaghetti” Bridge Model Using the Acoustic Emission Technique

by Boris Nahuel Rojo Tanzi, Mario Sobczyk, Tiago Becker, Luis Alberto Segovia González, Sabrina Vantadori, Ignacio Iturrioz and Giuseppe Lacidogna

Appl. Sci. 2021, 11(6), 2718; https://doi.org/10.3390/app11062718 - 18 Mar 2021

Cited by 6 | Viewed by 5714

Abstract

This paper applies the Acoustic Emission (AE) Technique to analyze the damage process in a one-meter span bridge model that was built from spaghetti sticks during a loading test. The AE signals are analyzed in terms of four coefficients that are evaluated as [...] Read more.

This paper applies the Acoustic Emission (AE) Technique to analyze the damage process in a one-meter span bridge model that was built from spaghetti sticks during a loading test. The AE signals are analyzed in terms of four coefficients that are evaluated as predictors of structure failure, with frequency variation appearing to be the strongest indicator of instability. The AE data are also compared to theoretical predictions that are given by the Bundle Model, confirming that underlying general patterns in damage processes are highly influenced by the geometric distribution of the structure and the loading pattern that is applied to it. Full article

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13 pages, 5479 KiB

Open AccessArticle

Use of Image Correlation to Measure Macroscopic Strains by Hygric Swelling in Sandstone Rocks

by Belén Ferrer, María-Baralida Tomás and David Mas

Appl. Sci. 2021, 11(6), 2495; https://doi.org/10.3390/app11062495 - 11 Mar 2021

Cited by 5 | Viewed by 1682

Abstract

Some materials undergo hygric expansion when soaked. In porous rocks, this effect is enhanced by the pore space, because it allows water to reach every part of its volume and to hydrate most swelling parts. In the vicinity, this enlargement has negative structural [...] Read more.

Some materials undergo hygric expansion when soaked. In porous rocks, this effect is enhanced by the pore space, because it allows water to reach every part of its volume and to hydrate most swelling parts. In the vicinity, this enlargement has negative structural consequences as adjacent elements support some compressions or displacements. In this work, we propose a normalized cross-correlation between rock surface texture images to determine the hygric expansion of such materials. We used small porous sandstone samples (11 × 11 × 30 mm³) to measure hygric swelling. The experimental setup comprised an industrial digital camera and a telecentric objective. We took one image every 5 min for 3 h to characterize the whole swelling process. An error analysis of both the mathematical and experimental methods was performed. The results showed that the proposed methodology provided, despite some limitations, reliable hygric swelling information by a non-contact methodology with an accuracy of 1 micron and permitted the deformation in both the vertical and horizontal directions to be explored, which is an advantage over traditional linear variable displacement transformers. Full article

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16 pages, 1338 KiB

Open AccessArticle

Non-Invasive Testing of Physical Systems Using Topological Sensitivity

by María Higuera, José M. Perales, María-Luisa Rapún and José M. Vega

Appl. Sci. 2021, 11(3), 1341; https://doi.org/10.3390/app11031341 - 2 Feb 2021

Cited by 2 | Viewed by 2650

Abstract

A review of available results on non-destructive testing of physical systems, using the concept of topological sensitivity, is presented. This mathematical tool estimates the sensitivity of a set of measurements in some given sensors, distributed along the system, to defects/flaws that produce a [...] Read more.

A review of available results on non-destructive testing of physical systems, using the concept of topological sensitivity, is presented. This mathematical tool estimates the sensitivity of a set of measurements in some given sensors, distributed along the system, to defects/flaws that produce a degradation of the system. Such degradation manifests itself on the properties of the system. The good performance of this general purpose post-processing method is reviewed and illustrated in some applications involving non-destructive testing. These applications include structural health monitoring, considering both elastodynamic ultrasonic guided Lamb waves and active infrared thermography. Related methods can also be used in other fields, such as diagnosis/prognosis of engineering devices, which is also considered. Full article

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17 pages, 15701 KiB

Open AccessArticle

3D Imaging of CRP and Ultrasonic Tomography to Detect Decay in a Living Adult Holm Oak (Quercus ilex L.) in Sardinia (Italy)

by Michele Puxeddu, Francesco Cuccuru, Silvana Fais, Giuseppe Casula and Maria Giovanna Bianchi

Appl. Sci. 2021, 11(3), 1199; https://doi.org/10.3390/app11031199 - 28 Jan 2021

Cited by 8 | Viewed by 3310

Abstract

A field-integrated methodology using 3D ultrasonic tomography supported by close range photogrammetry (CRP) has been developed and evaluated as a tool to detect the presence and patterns of decay forms in a living adult holm oak (Quercus ilex L.) in an urban [...] Read more.

A field-integrated methodology using 3D ultrasonic tomography supported by close range photogrammetry (CRP) has been developed and evaluated as a tool to detect the presence and patterns of decay forms in a living adult holm oak (Quercus ilex L.) in an urban green area of the city of Cagliari, Sardinia, Italy. Close range photogrammetry was used to compute a high resolution 3D model of the studied tree, texturized with natural colors. Moreover, following the implemented workflow process it was possible to evaluate the deformation pattern of the studied tree over time. In a second step of our integrated approach, and in order to diagnose the state of health of the inner part of the studied tree in a non-invasive way, laboratory and in situ non-invasive ultrasonic techniques were applied. The results of the close range photogrammetry analysis supported the optimal design of the 3D ultrasonic tomography of the living adult holm oak. Ultrasonic tomography is one of the most powerful non-destructive testing techniques for the full-volume inspection of a structure. It produced physical information on the inner structure of the stem of the investigated tree. The results of the study show that the integrated application of close range photogrammetry and 3D ultrasonic tomography is a powerful tool for a highly accurate and objective evaluation of the external and internal decay of trees and for monitoring their conservation states. With the fully integrated approach, the diagnostic process aimed to prevent instability and the failure of trees can be greatly improved. Full article

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15 pages, 10154 KiB

Open AccessArticle

Study of Materials Behavior in a Monumental Vault Strengthened by a Carbon Net in a Mineral Matrix Subjected to Seismic Influence

by Łukasz Bednarz, Izabela Drygała, Joanna Dulińska and Jerzy Jasieńko

Appl. Sci. 2021, 11(3), 1015; https://doi.org/10.3390/app11031015 - 23 Jan 2021

Cited by 4 | Viewed by 1959

Abstract

The application of the elasto-plastic material model known as the Barcelona Model (BM) for numerical assessment of a historical vault subjected to earthquake sequence is presented in this work. As a case study, part of a masonry vault erected in Southern Poland in [...] Read more.

The application of the elasto-plastic material model known as the Barcelona Model (BM) for numerical assessment of a historical vault subjected to earthquake sequence is presented in this work. As a case study, part of a masonry vault erected in Southern Poland in the 12th century was chosen. For the study purposes, a 3D finite element model (FEM) of the vault was prepared using the ABAQUS/Standard software program. The essential details of the structure geometry were taken from the 3D scan of the vault. The first variant of the masonry vault was the structure without any strengthening, whereas the second variant was with strengthening system realized by application on composite materials, i.e., the carbon fiber reinforced cementitious matrix (C-FRCM). The results of the dynamic analysis revealed that an evident nonlinear performance of the masonry materials of the vault in both cases was detected for both FE models of the structure. The analysis proved that the foreshock–mainshock–aftershock sequence caused substantial damages in structural parts of the masonry vault. The distribution of plastic strains and damages allowed assessment of the impact of the full seismic sequence on the masonry vault. In the case of the unstrengthen vault the level of cracking and stiffness loss reached 90%. In the case of the vault strengthened with the FRCM system the tensile damage level was significantly lower. It did not exceed 30%. In addition, the first plastic zone of the unstrengthened masonry structural elements of the vault became visible after the foreshock. Full article

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2020

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16 pages, 36354 KiB

Open AccessArticle

Feasibility of a Thermography Nondestructive Technique for Determining the Quality of Historical Frescoed Masonries: Applications on the Templar Church of San Bevignate

by Vittorio Gusella, Federico Cluni and Riccardo Liberotti

Appl. Sci. 2021, 11(1), 281; https://doi.org/10.3390/app11010281 - 30 Dec 2020

Cited by 8 | Viewed by 2447

Abstract

Thermography is a non-destructive and non-contact technique allowing, without taking samples, gaining information about several aspects of heritage buildings. This contribution presents the last phase of a research path, started with laboratory tests and now aimed at a real case of great cultural [...] Read more.

Thermography is a non-destructive and non-contact technique allowing, without taking samples, gaining information about several aspects of heritage buildings. This contribution presents the last phase of a research path, started with laboratory tests and now aimed at a real case of great cultural value, which involved the use of the thermal imaging camera to unveil in-depth defects and the wall texture, hidden by valuable plasters or frescoes, in order to correlate the quality of the masonry to its mechanical properties. For this, a method has been devised, made of an original integration of thermographic and post-processing techniques, and recently was applied for the first time to a real case study: the Italian Templar church of San Bevignate, part of an architectural complex from the 13th century located in the city of Perugia. The opportunity to establish the masonry quality of a historical building using non-destructive testing (NDT) represents a little-known possibility to frame not only important factors for the conservation of the frescoes but also information on the seismic vulnerability of historical masonry architectures in order to preserve the artefact from being damaged during the surveys and to plan any effective intervention of restoration and structural reinforcement. Full article

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17 pages, 6180 KiB

Open AccessArticle

Thermoelastic Investigation of Carbon-Fiber-Reinforced Composites Using a Drop-Weight Impact Test

by Zahra Andleeb, Sohail Malik, Hassan Abbas Khawaja, Anders Samuelsen Nordli, Ståle Antonsen, Ghulam Hussain and Mojtaba Moatamedi

Appl. Sci. 2021, 11(1), 207; https://doi.org/10.3390/app11010207 - 28 Dec 2020

Cited by 5 | Viewed by 4287

Abstract

Composite materials are becoming more popular in technological applications due to the significant weight savings and strength offered by these materials compared to metallic materials. In many of these practical situations, the structures suffer from drop-impact loads. Materials and structures significantly change their [...] Read more.

Composite materials are becoming more popular in technological applications due to the significant weight savings and strength offered by these materials compared to metallic materials. In many of these practical situations, the structures suffer from drop-impact loads. Materials and structures significantly change their behavior when submitted to impact loading conditions compared to quasi-static loading. The present work is devoted to investigating the thermal process in carbon-fiber-reinforced polymers (CFRP) subjected to a drop test. A novel drop-weight impact test experiment is performed to evaluate parameters specific to 3D composite materials. A strain gauge rosette and infrared thermography are employed to record the kinematic and thermal fields on the composites’ surfaces. This technique is nondestructive and offers an extensive full-field investigation of a material’s response. The combination of strain and infrared thermography data allows a comprehensive analysis of thermoelastic effects in CFRP when subjected to impacts. The experimental results are validated using numerical analysis by developing a MATLAB^® code to analyze whether the coupled heat and wave equation phenomenon exists in a two-dimensional polar coordinate system by discretizing through a forward-time central-space (FTCS) finite-difference method (FDM). The results show the coupling has no significant impact as the waves generated due to impact disappears in 0.015 s. In contrast, heat diffusion happens for over a one-second period. This study demonstrates that the heat equation alone governs the CFRP heat flow process, and the thermoelastic effect is negligible for the specific drop-weight impact load. Full article

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16 pages, 2426 KiB

Open AccessArticle

Enhancement of a New Methodology Based on the Impulse Excitation Technique for the Nondestructive Determination of Local Material Properties in Composite Laminates

by Carlo Boursier Niutta

Appl. Sci. 2021, 11(1), 101; https://doi.org/10.3390/app11010101 - 24 Dec 2020

Cited by 7 | Viewed by 2037

Abstract

A new approach for the nondestructive determination of the elastic properties of composite laminates is presented. The approach represents an improvement of a recently published experimental methodology based on the Impulse Excitation Technique, which allows nondestructively assessing local elastic properties of composite laminates [...] Read more.

A new approach for the nondestructive determination of the elastic properties of composite laminates is presented. The approach represents an improvement of a recently published experimental methodology based on the Impulse Excitation Technique, which allows nondestructively assessing local elastic properties of composite laminates by isolating a region of interest through a proper clamping system. Different measures of the first resonant frequency are obtained by rotating the clamping system with respect to the material orientation. Here, in order to increase the robustness of the inverse problem, which determines the elastic properties from the measured resonant frequencies, information related to the modal shape is retained by considering the effect of an additional concentrated mass on the first resonant frequency. According to the modal shape and the position of the mass, different values of the first resonant frequency are obtained. Here, two positions of the additional mass, i.e., two values of the resonant frequency in addition to the unloaded frequency value, are considered for each material orientation. A Rayleigh–Ritz formulation based on higher order theory is adopted to compute the first resonant frequency of the clamped plate with concentrated mass. The elastic properties are finally determined through an optimization problem that minimizes the discrepancy on the frequency reference values. The proposed approach is validated on several materials taken from the literature. Finally, advantages and possible limitations are discussed. Full article

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11 pages, 2385 KiB

Open AccessArticle

Analysis of Surface Roughness Influence in Non-Destructive Magnetic Measurements Applied to Reactor Pressure Vessel Steels

by Gábor Vértesy, Antal Gasparics, James M. Griffin, Jino Mathew, Michael E. Fitzpatrick and Inge Uytdenhouwen

Appl. Sci. 2020, 10(24), 8938; https://doi.org/10.3390/app10248938 - 15 Dec 2020

Cited by 13 | Viewed by 2269

Abstract

The influence of surface roughness on magnetic measurements of Reactor Pressure Vessel Steels was investigated by applying two types of magnetic, non-destructive measurement on nuclear reactor pressure vessel steel samples: magnetic adaptive testing (MAT) and magnetic Barkhausen noise measurement (MBN). The surface roughness [...] Read more.

The influence of surface roughness on magnetic measurements of Reactor Pressure Vessel Steels was investigated by applying two types of magnetic, non-destructive measurement on nuclear reactor pressure vessel steel samples: magnetic adaptive testing (MAT) and magnetic Barkhausen noise measurement (MBN). The surface roughness was modified by primary and secondary machine cutting forces. Different settings of machine cutting produced different surface conditions. It was found that for both measurements a monotonic correlation was found to exist between magnetic parameters and surface roughness. Results of the MAT measurements found that the correlation depends on the speed (i.e., on the applied slew rate) of the magnetizing current. In a similar fashion, results from the MBN method show good agreement with MAT, where the response diminishes with an increase in surface roughness. The results show the importance of accounting for surface condition in the interpretation of results of non-destructive magnetic testing. Full article

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15 pages, 2576 KiB

Open AccessArticle

Edge Effect Analysis and Edge Defect Detection of Titanium Alloy Based on Eddy Current Testing

by Yuedong Xie, Jiyao Li, Yang Tao, Shupei Wang, Wuliang Yin and Lijun Xu

Appl. Sci. 2020, 10(24), 8796; https://doi.org/10.3390/app10248796 - 9 Dec 2020

Cited by 20 | Viewed by 3390

Abstract

Titanium alloy is widely used in the area of aerospace and aviation due to its excellent properties. Eddy current testing (ECT) is among the most extensively used non-destructive techniques for titanium alloy material inspection. However, most previous research has focused on inspecting defects [...] Read more.

Titanium alloy is widely used in the area of aerospace and aviation due to its excellent properties. Eddy current testing (ECT) is among the most extensively used non-destructive techniques for titanium alloy material inspection. However, most previous research has focused on inspecting defects far from the edge of the material. It is a challenging task for edge crack detection because of edge effect. This study aims to investigate the influences of sensor parameters on edge effect and defect detection capability, and in the meantime, optimize sensor parameters to improve the capability of edge defect detection. The simulation method for edge effect evaluation is proposed including the 2^k factorial design used for factor screening, and the regression model is fitted and validated for sensor design and optimization for edge defect detection. A simulation scheme is designed to investigate the defect detection capability. An approach comprehensively analyzing the influence of coil parameters on edge effect and defect detection capability is applied to determine the optimal coil parameters for edge defect detection. Full article

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17 pages, 1900 KiB

Open AccessArticle

MIMO LS-SVR-Based Multi-Point Vibration Response Prediction in the Frequency Domain

by Cheng Wang, Delei Chen, Haiyang Huang, Wei Zhan, Xiongming Lai and Jianwei Chen

Appl. Sci. 2020, 10(24), 8784; https://doi.org/10.3390/app10248784 - 8 Dec 2020

Cited by 6 | Viewed by 2088

Abstract

To predict the multi-point vibration response in the frequency domain when the uncorrelated multi-source loads are unknown, a data-driven and multi-input multi-output least squares support vector regression (MIMO LS-SVR)-based method in the frequency domain is proposed. Firstly, the relationship between the measured multi-point [...] Read more.

To predict the multi-point vibration response in the frequency domain when the uncorrelated multi-source loads are unknown, a data-driven and multi-input multi-output least squares support vector regression (MIMO LS-SVR)-based method in the frequency domain is proposed. Firstly, the relationship between the measured multi-point vibration response and unmeasured multi-point vibration response is formulated using the transfer function in the frequency domain. Secondly, the data-driven multiple regression analysis problem of multi-point vibration response prediction in the frequency domain is described formally, and its mathematical model is established. With the measured multi-point vibration response as the input and the unmeasured multi-point vibration response as the output, the vibration response history data are assembled as a MIMO training dataset at each frequency. Thirdly, using the MIMO LS-SVR algorithm and MIMO history training dataset, the multi-point vibration response prediction model is built at each frequency point. By comparing the transmissibility matrix method, multiple linear regression model-based method, and MIMO neural network method, the application scope of the proposed method and its advantages are analyzed. The experimental results for acoustic and vibration experiment on a cylindrical shell verified that the MIMO LS-SVR-based method predicts the multi-point vibration response effectively when the loads are unknown, and has higher precision than the transfer function method, multiple linear regression method, MIMO neural network method, and transmissibility matrix method. Full article

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16 pages, 3248 KiB

Open AccessArticle

Response of a Tensegrity Simplex in Experimental Tests of a Modal Hammer at Different Self-Stress Levels

by Leszek Małyszko and Andrzej Rutkiewicz

Appl. Sci. 2020, 10(23), 8733; https://doi.org/10.3390/app10238733 - 6 Dec 2020

Cited by 2 | Viewed by 2949

Abstract

The natural frequencies and eigenmodes of the tensegrity simplex are determined experimentally in impact hammer tests. To study an effect of prestressing, the tests are carried out on a physical model 1.2 m high and 0.5 m diameter with build-in transducers for measuring [...] Read more.

The natural frequencies and eigenmodes of the tensegrity simplex are determined experimentally in impact hammer tests. To study an effect of prestressing, the tests are carried out on a physical model 1.2 m high and 0.5 m diameter with build-in transducers for measuring actual values of forces in cables at 13 prestress levels. The recorded data for each pre-stress level from three three-axial accelerometers are combined to extract the first five natural frequencies and modes by means of the method of experimental modal analysis. It was experimentally confirmed that the first rotational frequency depends on the pre-stress level and its sensitivity to the self-stress state is high enough to be successfully used in vibrational health monitoring. A proprietary formula was proposed for the relationship between frequency and the pre-stress level to control the dynamic properties of the simplex. An excellent comparison between the experimental results of the frequency and the formula was obtained. A comparison of numerical results of the finite element method with truss element and experiment is also shown. Full article

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14 pages, 5546 KiB

Open AccessArticle

AE-RTISNet: Aeronautics Engine Radiographic Testing Inspection System Net with an Improved Fast Region-Based Convolutional Neural Network Framework

by Zhi-Hao Chen and Jyh-Ching Juang

Appl. Sci. 2020, 10(23), 8718; https://doi.org/10.3390/app10238718 - 5 Dec 2020

Cited by 10 | Viewed by 2865

Abstract

To ensure safety in aircraft flying, we aimed to use deep learning methods of nondestructive examination with multiple defect detection paradigms for X-ray image detection. The use of the fast region-based convolutional neural network (Fast R-CNN)-driven model was to augment and improve the [...] Read more.

To ensure safety in aircraft flying, we aimed to use deep learning methods of nondestructive examination with multiple defect detection paradigms for X-ray image detection. The use of the fast region-based convolutional neural network (Fast R-CNN)-driven model was to augment and improve the existing automated non-destructive testing (NDT) diagnosis. Within the context of X-ray screening, limited numbers and insufficient types of X-ray aeronautics engine defect data samples can, thus, pose another problem in the performance accuracy of training models tackling multiple detections. To overcome this issue, we employed a deep learning paradigm of transfer learning tackling both single and multiple detection. Overall, the achieved results obtained more than 90% accuracy based on the aeronautics engine radiographic testing inspection system net (AE-RTISNet) retrained with eight types of defect detection. Caffe structure software was used to perform network tracking detection over multiple Fast R-CNNs. We determined that the AE-RTISNet provided the best results compared with the more traditional multiple Fast R-CNN approaches, which were simple to translate to C++ code and installed in the Jetson^™ TX2 embedded computer. With the use of the lightning memory-mapped database (LMDB) format, all input images were 640 × 480 pixels. The results achieved a 0.9 mean average precision (mAP) on eight types of material defect classifier problems and required approximately 100 microseconds. Full article

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10 pages, 6924 KiB

Open AccessArticle

Automatic Detection of Welding Defects Using Faster R-CNN

by Sang-jin Oh, Min-jae Jung, Chaeog Lim and Sung-chul Shin

Appl. Sci. 2020, 10(23), 8629; https://doi.org/10.3390/app10238629 - 2 Dec 2020

Cited by 44 | Viewed by 5185

Abstract

In the shipbuilding industry, the non-destructive testing for welding quality inspection is mainly used for the permanent storage of the testing results and the radio-graphic testing which can visually inspect the interior of the welded part. Experts are required to properly detect the [...] Read more.

In the shipbuilding industry, the non-destructive testing for welding quality inspection is mainly used for the permanent storage of the testing results and the radio-graphic testing which can visually inspect the interior of the welded part. Experts are required to properly detect the test results and it takes a lot of time and cost to manually Interpret the radio-graphic testing image of the structure over 500 blocks. The algorithms that automatically interpret the existing radio-graphic testing images to extract features through image pre-processing and classify the defects using neural networks, and only partial automation is performed. In order to implement the feature extraction and classification in one algorithm and to implement the overall automation, this paper proposes a method of automatically detecting welding defect using Faster R-CNN which is a deep learning basis. We analyzed the data to learn algorithms and compared the performance improvements using data augmentation method to artificially increase the limited data. In order to appropriately extract the features of the radio-graphic testing image, two internal feature extractors of Faster R-CNN were selected, compared, and performance evaluation was performed. Full article

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23 pages, 10695 KiB

Open AccessArticle

Damage Detection Method Based on Continuous Wavelet Transformation of Lamb Wave Signals

by M. Saqib Hameed, Zheng Li and Kaihong Zheng

Appl. Sci. 2020, 10(23), 8610; https://doi.org/10.3390/app10238610 - 1 Dec 2020

Cited by 21 | Viewed by 3237

Abstract

A damage estimation method based on continuous wavelet transformation (CWT) of the normalized Lamb wave signals is proposed here. Lamb waves are actuated and sensed using piezoelectric (lead zirconate titanate, PZT) transducers arranged in the form of square detection cells on a plate-like [...] Read more.

A damage estimation method based on continuous wavelet transformation (CWT) of the normalized Lamb wave signals is proposed here. Lamb waves are actuated and sensed using piezoelectric (lead zirconate titanate, PZT) transducers arranged in the form of square detection cells on a plate-like structure. Excitation sequences based on pitch–catch and pulse–echo configurations are tested for the same arrangement of the transducers. The possibilities of the existence of damage for each actuator–senor pair are formed by using the normalized coefficient of CWT. The size of the possible damage region is directly controlled through envelopes defined by the coefficients of CWT, and no additional parameter is required to define its size. The aggregate damage image is constructed by the fusion of damage possibilities from all actuator–sensor pairs using damage indices based on conjunctive and compromised fusion schemes. The results indicate that the proposed method can estimate the location and severity of multiple damage with signals directly from the damaged plate, without the need of baseline signals from the undamaged plate, and the time-compensated signals provide better damage imaging than the raw signals. The most accurate and computationally inexpensive combination is the pulse–echo configuration with damage index based on conjunctive image fusion scheme. The method is computationally inexpensive and can be applied for multiple damage estimations in large structures to reduce the evaluation cost and inspection time during on-line structural health monitoring. Full article

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19 pages, 5189 KiB

Open AccessArticle

Comparison of Nondestructive Testing Methods for Solder, Sinter, and Adhesive Interconnects in Power and Opto-Electronics

by Maximilian Schmid, Sri Krishna Bhogaraju, E Liu and Gordon Elger

Appl. Sci. 2020, 10(23), 8516; https://doi.org/10.3390/app10238516 - 28 Nov 2020

Cited by 18 | Viewed by 3843

Abstract

Reliability is one of the major requirements for power and opto-electronic devices across all segments. High operation temperature and/or high thermomechanical stress cause defects and degradation of materials and interconnects, which may lead to malfunctions with costly or even life-threatening consequences. To avoid [...] Read more.

Reliability is one of the major requirements for power and opto-electronic devices across all segments. High operation temperature and/or high thermomechanical stress cause defects and degradation of materials and interconnects, which may lead to malfunctions with costly or even life-threatening consequences. To avoid or at least reduce failures, nondestructive testing (NDT) methods are common within development and production of power and opto-electronics. Currently, the dominating NDT methods are X-ray, scanning acoustic microscopy (SAM), and transient thermal analysis (TTA). However, they have different strengths and weaknesses with respect to materials and mechanical designs. This paper compares these NDT methods for different interconnect technologies, i.e., reflow soldering, adhesive, and sintered interconnection. While X-ray provided adequate results for soldered interfaces, inspection of adhesives and sintered interconnects was not possible. With SAM, evaluation of adhesives and sintered interconnects was also feasible, but quality depended strongly on the sample under test. TTA enabled sufficiently detailed results for all the interconnect applications. Automated TTA equipment, as the in-house developed tester used within this investigation, enabled measurement times compatible with SAM and X-ray. In the investigations, all methods revealed their pros and cons, and their selection has to depend on the sample under tests and the required analysis depth and data details. In the paper, guidelines are formulated for an appropriate decision on the NDT method depending on sample and requirements. Full article

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19 pages, 8190 KiB

Open AccessArticle

Identification of Unstable Subsurface Rock Structure Using Ground Penetrating Radar: An EEMD-Based Processing Method

by Yang Jin and Yunling Duan

Appl. Sci. 2020, 10(23), 8499; https://doi.org/10.3390/app10238499 - 28 Nov 2020

Cited by 4 | Viewed by 2778

Abstract

Surrounding rock quality of underground caverns is crucial to structural safety and stability in geological engineering. Classic measures for rock quality investigation are destructive and time consuming, and therefore technology evolution for efficiently evaluating rock quality is significantly required. In this paper, the [...] Read more.

Surrounding rock quality of underground caverns is crucial to structural safety and stability in geological engineering. Classic measures for rock quality investigation are destructive and time consuming, and therefore technology evolution for efficiently evaluating rock quality is significantly required. In this paper, the non-destructive technology ground penetrating radar (GPR) assisted by an ensemble empirical mode decomposition (EEMD)-based signal processing approach is investigated for identifying unstable subsurface rock structures. By decomposing the pre-processed GPR signals into multiple intrinsic mode functions (IMFs) and residues, one typical IMF can preserve the distinct local modes and is considered to reconstruct the subterranean profile. Promising results have been achieved in simple scenarios and filed measurements. The reconstructed profiles can accurately illustrate the subsurface interfaces and eliminate the interference signals. Unstable rock structures have been identified in further field applications. Therefore, the developed approach is efficient in unstable rock structure identification. Full article

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9 pages, 1816 KiB

Open AccessArticle

Developing Guidelines for the Use of Passive Thermography on Cultural Heritage in Tropical Climates

by Manogna Kavuru and Elisabetta Rosina

Appl. Sci. 2020, 10(23), 8411; https://doi.org/10.3390/app10238411 - 26 Nov 2020

Cited by 2 | Viewed by 2420

Abstract

Infrared thermography (IRT) has been a very successful tool for the diagnosis and monitoring of cultural heritage restoration projects. It has been used to identify anomalies, moisture issues, etc., in historic buildings. Although it is a promising tool, one of the limitations is [...] Read more.

Infrared thermography (IRT) has been a very successful tool for the diagnosis and monitoring of cultural heritage restoration projects. It has been used to identify anomalies, moisture issues, etc., in historic buildings. Although it is a promising tool, one of the limitations is that a method to deploy it onsite has not been standardized. This is due to the different variables that might affect thermal signatures captured by the thermal camera, when onsite. Especially since environmental conditions play a major role in thermography, the process must vary from region to region significantly. That said, efforts have been made over the years to establish some base standards for designated purposes of infrared thermography in the construction field. These standards and best practice methods, although comprehensive, do not effectively help with issues that are contextual to the location of the building, for instance, tropical climates, such as India. This paper aims to suggest guidelines for a passive approach of thermography, based on practical applications and procedures followed during the thermographic survey at the former British Residency in Hyderabad, India. Additionally, this paper explores the avenues through which region specific guidelines can be established. Full article

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13 pages, 4672 KiB

Open AccessArticle

MEMS Vibrational Power Generator for Bridge Slab and Pier Health Monitoring

by Katsufumi Hashimoto, Tomoki Shiotani, Hiroyuki Mitsuya and Kai-Chun Chang

Appl. Sci. 2020, 10(22), 8258; https://doi.org/10.3390/app10228258 - 21 Nov 2020

Cited by 7 | Viewed by 2911

Abstract

Micro energy harvesters (MEH) based on microelectromechanical systems (MEMS) are rapidly developing, providing a green and virtually infinite energy source. The electrostatic vibratory power generator outputs electric power when it vibrates, motivating us to apply it to vibrating civil infrastructures excited by ambient [...] Read more.

Micro energy harvesters (MEH) based on microelectromechanical systems (MEMS) are rapidly developing, providing a green and virtually infinite energy source. The electrostatic vibratory power generator outputs electric power when it vibrates, motivating us to apply it to vibrating civil infrastructures excited by ambient and daily traffic loadings. In this study, an innovative monitoring system utilizing MEH devices was proposed for detecting slab damage and pier scours for bridge structures. Its performance was numerically investigated with finite element models, where the damage in slabs was modeled with a reduced Young’s modulus and scours with fixed boundaries of inclined depth. It was shown that the powers generated at each MEH varied as the target structure’s modal frequency shifted and amplitude changed by damage or scour. A power generation index was proposed to identify slab damage and a reference-free method was introduced to detect uneven pier scours. Utilizing an electrostatic vibration-based MEH (MEMS vibrational power generator), this pioneering study showed that MEMS vibrational power generators can work as sensors for an infrastructure structural health monitoring system. Full article

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12 pages, 1908 KiB

Open AccessArticle

Application of Wavelet Transform to Damage Identification in the Steel Structure Elements

by Anna Knitter-Piątkowska and Arkadiusz Dobrzycki

Appl. Sci. 2020, 10(22), 8198; https://doi.org/10.3390/app10228198 - 19 Nov 2020

Cited by 13 | Viewed by 2256

Abstract

This work concerns the concept and verification of the experimental possibility of using a wavelet transform to assess a steel structure’s condition. In the research, a developed measuring stand was used. Mechanical waves in the metal plate were excited by the impact. These [...] Read more.

This work concerns the concept and verification of the experimental possibility of using a wavelet transform to assess a steel structure’s condition. In the research, a developed measuring stand was used. Mechanical waves in the metal plate were excited by the impact. These waves were recorded with an electroacoustic transducer and registered in the form of electrical signals. Both the signals generated by the actuator of the plate and the signals reaching the transducer were recorded. The registered data were decomposed into wavelet coefficients. Laboratory tests have shown the possibility of applying this type of test to identify damage in steel structural elements—the relationship between the details of the wavelet transform and the type of damage was demonstrated. Full article

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15 pages, 6874 KiB

Open AccessArticle

NDT Methods Suitable for Evaluation the Condition of Military Fortification Construction in the Field

by Zezulová Eva, Hasilová Kamila, Komárková Tereza, Stoniš Patrik, Štoller Jiří and Anton Ondřej

Appl. Sci. 2020, 10(22), 8161; https://doi.org/10.3390/app10228161 - 18 Nov 2020

Cited by 16 | Viewed by 2190

Abstract

The protective structure is designed to protect the live force against the impact of a shock wave and projectiles, it cannot be diagnosed by the destructive method which devalues the protective structure by sampling. The authors are looking for a combination of suitable [...] Read more.

The protective structure is designed to protect the live force against the impact of a shock wave and projectiles, it cannot be diagnosed by the destructive method which devalues the protective structure by sampling. The authors are looking for a combination of suitable non-destructive technology (NDT) methods that would be used in the future to prove the degree of damage to cement-based protective structures after an explosion. This article represents the first part of an experiment designed to verify the applicability of NDT methods, to evaluate the degree of damage of the protective structure in the field. The experiment consists of three parts. The first part is a laboratory verification of the initial material characteristics of the materials used. The first test set of structural elements is made of steel fiber-reinforced concrete. The elements are evaluated using NDT methods and for comparison by destructive laboratory methods. The second part is the impact of structures using explosion and evaluation of the condition of structures using NDT methods in the field. The last part is used to verify the results of the NDT method, which ensures the residual strength of the structure in the laboratory and try to find the relationship between changes in the results of NDT methods and the residual strength. Radiography was included in the introductory and concluding parts of the experiment to verify the results. Although this method is not suitable for using in-situ, it is the only standardized method of the NDT methods used. Full article

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18 pages, 4194 KiB

Open AccessArticle

New System to Determine the Evolution of the Dynamic Young’s Modulus from Early Ages in Masonry Mortars

by Engerst Yedra, Daniel Ferrández, Carlos Morón and Edmundo Gómez

Appl. Sci. 2020, 10(22), 8129; https://doi.org/10.3390/app10228129 - 17 Nov 2020

Cited by 6 | Viewed by 2308

Abstract

This work presents a new method to determine the evolution of the dynamic Young’s modulus (MOE) from small mechanical disturbances caused by cement mortar samples and whose value is collected using a low-cost Arduino accelerometer. The results obtained are correlated with measurements made [...] Read more.

This work presents a new method to determine the evolution of the dynamic Young’s modulus (MOE) from small mechanical disturbances caused by cement mortar samples and whose value is collected using a low-cost Arduino accelerometer. The results obtained are correlated with measurements made using traditional ultrasound techniques, in addition to the evolution of MOE being related to the variation in mechanical properties that cement mortars experience over time. In this way, in this work, a secure application method is presented that allows us to advance the knowledge of construction materials with the incorporation of construction and demolition waste (CDW) and—more specifically—of cement mortars made with aggregates recycled from ceramic or concrete waste. Full article

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13 pages, 3248 KiB

Open AccessArticle

A Novel Joint Localization Method for Acoustic Emission Source Based on Time Difference of Arrival and Beamforming

by Xiaoran Wang, Xiandong Liu, Tian He, Junfei Tai and Yingchun Shan

Appl. Sci. 2020, 10(22), 8045; https://doi.org/10.3390/app10228045 - 13 Nov 2020

Cited by 10 | Viewed by 2194

Abstract

Time difference of arrival (TDOA) method and beamforming method are often individually utilized in the localization of acoustic emission source of a plate. Based on the performances of the two methods, a novel joint localization method for acoustic emission source is proposed in [...] Read more.

Time difference of arrival (TDOA) method and beamforming method are often individually utilized in the localization of acoustic emission source of a plate. Based on the performances of the two methods, a novel joint localization method for acoustic emission source is proposed in this paper. Firstly, the performances of TDOA method and beamforming method are studied based on the simulation signals. Then, aiming at the advantages and disadvantages of these two methods, a joint localization method is proposed. Finally, the performances of joint localization method are verified by simulation and experiment. Both simulation and experimental results show that the accuracy of the joint localization method is improved, and the calculation amount is greatly reduced in comparison to the TDOA method and the beamforming method. Full article

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12 pages, 2937 KiB

Open AccessArticle

Identification of Multiple Local Damage to an Offshore Jacket Substructure Using a Novel Strain Expansion–Reduction Approach

by Jia-Hao He, Ding-Peng Liu, Cheng-Hsien Chung and Hsin-Haou Huang

Appl. Sci. 2020, 10(22), 7991; https://doi.org/10.3390/app10227991 - 11 Nov 2020

Cited by 3 | Viewed by 1774

Abstract

Modal parameter monitoring is a widely used structural health monitoring method. However, among other limitations, this method cannot effectively identify slight damage under ambient conditions. This study proposed a novel strain expansion–reduction approach for identifying damage. To verify the feasibility of the proposed [...] Read more.

Modal parameter monitoring is a widely used structural health monitoring method. However, among other limitations, this method cannot effectively identify slight damage under ambient conditions. This study proposed a novel strain expansion–reduction approach for identifying damage. To verify the feasibility of the proposed method, we numerically and experimentally tested the method using a rigid acrylic frame. The frame was artificially damaged at various depths to reflect various damage scenarios. The increase in the damage index provided an accurate estimation of damage severity. For the case with merely 0.5% damage zone in one slat, the index is increased by 259% of the intact case. When the damage zone was doubled, the index increases significantly by 467% of the intact case, demonstrating excellent sensitivity of the proposed method. To guarantee practical use, the numerical model of the proposed method was applied to an offshore wind turbine jacket substructure and successfully identified multiple damage sites and the damage severity with extremely high (>10) damage index. Full article

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17 pages, 3675 KiB

Open AccessArticle

A Multiobjective Perspective to Optimal Sensor Placement by Using a Decomposition-Based Evolutionary Algorithm in Structural Health Monitoring

by Tsung-Yueh Lin, Jin Tao and Hsin-Haou Huang

Appl. Sci. 2020, 10(21), 7710; https://doi.org/10.3390/app10217710 - 30 Oct 2020

Cited by 10 | Viewed by 2397

Abstract

The objective of optimal sensor placement in a dynamic system is to obtain a sensor layout that provides as much information as possible for structural health monitoring (SHM). Whereas most studies use only one modal assurance criterion for SHM, this work considers two [...] Read more.

The objective of optimal sensor placement in a dynamic system is to obtain a sensor layout that provides as much information as possible for structural health monitoring (SHM). Whereas most studies use only one modal assurance criterion for SHM, this work considers two additional metrics, signal redundancy and noise ratio, combining into three optimization objectives: Linear independence of mode shapes, dynamic information redundancy, and vibration response signal strength. A modified multiobjective evolutionary algorithm was combined with particle swarm optimization to explore the optimal solution sets. In the final determination, a multiobjective decision-making (MODM) strategy based on distance measurement was used to optimize the aforementioned objectives. We applied it to a reduced finite-element beam model of a reference building and compared it with other selection methods. The results indicated that MODM suitably balanced the objective functions and outperformed the compared methods. We further constructed a three-story frame structure for experimentally validating the effectiveness of the proposed algorithm. The results indicated that complete structural modal information can be effectively obtained by applying the MODM approach to identify sensor locations. Full article

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11 pages, 8840 KiB

Open AccessArticle

THz Reflective Imaging System Utilizing Broadband Homodyne Amplification for Artifact-Free See-Through Imaging

by Kiwon Moon, Il-Min Lee, Eui Su Lee and Kyung Hyun Park

Appl. Sci. 2020, 10(20), 7228; https://doi.org/10.3390/app10207228 - 16 Oct 2020

Cited by 1 | Viewed by 2393

Abstract

Terahertz (THz) technology offers unique see-through imaging capability for various non-destructive inspection applications. In this work, we implemented a broadband continuous-wave THz imaging system to study technical issues related to the see-through imaging, including frequency-dependent resolution, material loss, and interference-induced artifacts. The interference-induced [...] Read more.

Terahertz (THz) technology offers unique see-through imaging capability for various non-destructive inspection applications. In this work, we implemented a broadband continuous-wave THz imaging system to study technical issues related to the see-through imaging, including frequency-dependent resolution, material loss, and interference-induced artifacts. The interference-induced false contrast and artifacts were observed, which were suppressed by broadband imaging techniques adopting the homodyne signal amplification by interferometric setup to overcome the material loss. Full article

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18 pages, 7595 KiB

Open AccessArticle

Application of Metal Magnetic Memory Testing Technology to the Detection of Stress Corrosion Defect

by Bingxun Zhao, Kai Yao, Libo Wu, Xinglong Li and Yue-Sheng Wang

Appl. Sci. 2020, 10(20), 7083; https://doi.org/10.3390/app10207083 - 12 Oct 2020

Cited by 24 | Viewed by 2944

Abstract

The damage of equipment manufactured with ferromagnetic materials in service can be effectively detected by Metal Magnetic Memory Testing (MMMT) technology, which has received extensive attention in various industry fields. The effect of stress or strain on Magnetic Flux Leakage (MFL) signals of [...] Read more.

The damage of equipment manufactured with ferromagnetic materials in service can be effectively detected by Metal Magnetic Memory Testing (MMMT) technology, which has received extensive attention in various industry fields. The effect of stress or strain on Magnetic Flux Leakage (MFL) signals of ferromagnetic materials has been researched by many scholars for assessing stress concentration and fatigue damage. However, there is still a lack of research on the detection of stress corrosion damage of ferromagnetic materials by MMMT technology. In this paper, the electrochemical corrosion system was designed for corrosion experiments, and three different experiments were performed to study the effect of corrosion on MFL signals. The distribution of MFL signals on the surface of the specimen was investigated. The results indicated that both the normal component H_n and tangential component H_t of MFL signals presented different signal characteristics when the specimen was subjected to different working conditions. Finally, two characterization parameters, S_n and S_t, were defined to evaluate the corrosion degree of the specimen, and S_t is better. The direct dependence of corrosion depth on the parameter was developed and the average error rates between the predicted and measured values are 8.94% under the same working condition. Therefore, the expression can be used to evaluate the corrosion degree of the specimen quantitatively. The results are significant for detecting and assessing the corrosion defect of ferromagnetic materials. Full article

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21 pages, 41666 KiB

Open AccessArticle

The Spec-Radiation Method as a Fast Alternative to the Re-Radiation Method for the Detection of Flaws in Wooden Particleboards

by Andreas Sebastian Schmelt and Jens Twiefel

Appl. Sci. 2020, 10(19), 6663; https://doi.org/10.3390/app10196663 - 23 Sep 2020

Cited by 2 | Viewed by 2328

Abstract

For real-time evaluation of non-destructive air-coupled ultrasonic testing of wood-based materials, efficient and reliable calculation methods from ultrasonic holography are essential. Presented here is the spec-radiation method as a fast alternative to the re-radiation method. The spec-radiation method offers a more accurate and [...] Read more.

For real-time evaluation of non-destructive air-coupled ultrasonic testing of wood-based materials, efficient and reliable calculation methods from ultrasonic holography are essential. Presented here is the spec-radiation method as a fast alternative to the re-radiation method. The spec-radiation method offers a more accurate and up to 88% faster evaluation than the re-radiation method for the determination of flaws in particleboards. Flaws of sub-wavelength sizes can be identified and their shape and location can be determined with this method. The spec-radiation method produces a better reproduction of the sound field than the re-radiation method, especially in the area of the measuring plane. Full article

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14 pages, 6481 KiB

Open AccessArticle

Analysis of Local Damages Effect on Mechanical Responses of Underwater Shield Tunnel via Field Testing and Numerical Simulation

by Xuyan Tan, Weizhong Chen, Luyu Wang and Jianping Yang

Appl. Sci. 2020, 10(18), 6575; https://doi.org/10.3390/app10186575 - 21 Sep 2020

Cited by 4 | Viewed by 2497

Abstract

The investigation of concrete structural performance is crucial to maintain the stability of infrastructure. In order to assess structural stability, this work focuses on the development of an integrated framework to detect damaged conditions in the field and analyze their effect on mechanical [...] Read more.

The investigation of concrete structural performance is crucial to maintain the stability of infrastructure. In order to assess structural stability, this work focuses on the development of an integrated framework to detect damaged conditions in the field and analyze their effect on mechanical performance through nondestructive testing (NDT) technology and numerical models. First, a ground penetrating radar (GPR) and an infrared camera work collaboratively to identify the damaged positions of the concrete structure, with parameters calibrated by laboratory experiments. Then, a finite element model is established to study structural mechanical performance based on field conditions and detected results. In addition, the influenced regions induced by local damage are studied under different boundary conditions. As a case study, the devised method was employed in the Nanjing Yangtze River tunnel for stability assessment and disaster prevention. The detected results of the damaged conditions agree well with the actual conditions in the field. Numerical results show that the circumferential stress component is more significant than that observed longitudinally. The effect of local damage on stress implies a positive correlation with the rise of water pressure, in which the maximum stress response to the variation of water level is 45KPa per meter. Full article

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16 pages, 7601 KiB

Open AccessArticle

Electromagnetic Acoustic Detection of Steel Plate Defects Based on High-Energy Pulse Excitation

by Suzhen Liu, Ke Chai, Chuang Zhang, Liang Jin and Qingxin Yang

Appl. Sci. 2020, 10(16), 5534; https://doi.org/10.3390/app10165534 - 11 Aug 2020

Cited by 10 | Viewed by 2943

Abstract

The conventional electromagnetic ultrasonic transducers (EMATs) rely on the static magnetic field created by magnets. The magnet increases the size of the EMATs, and the strong magnetic force of the magnet attracts the detected steel and even ferromagnetic particles. It can cause mechanical [...] Read more.

The conventional electromagnetic ultrasonic transducers (EMATs) rely on the static magnetic field created by magnets. The magnet increases the size of the EMATs, and the strong magnetic force of the magnet attracts the detected steel and even ferromagnetic particles. It can cause mechanical damage to the transducer and the detected objects. A new high-energy acoustic excitation system, without a static bias magnetic is designed, which does not include any magnets. As the core of the system, the high-energy pulse excitation power supplies a transient high voltage to the excitation coil by the LC oscillation circuit. The maximum amplitude of current can reach 1700 A, which is much larger than the current in the conventional EMATs. Compared with the conventional EMATs, the intensity of the ultrasonic signal is greatly strengthened and the size of the EMAT is effectively reduced. Therefore, it can detect high-temperature steel plates at a higher lift-off distance. In this paper, the transduction mechanism of high-energy pulse electromagnetic acoustic on ferromagnetic materials was studied, and the high-energy pulse excitation coil used for the A0 mode Lamb wave was designed. The interaction rule of the magnetic field, the force field, and the acoustic field, was obtained. Then, the EMAT lift-off characteristic experiment of the high-energy pulse excitation was carried out, and the defect detection experiment was conducted on a cracked steel plate. The results show that the A0 mode Lamb waves have caused a high signal-to-noise ratio and can accurately locate the crack, which has a great advantage in detecting the microcrack defects of ferromagnetic materials. Full article

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30 pages, 6480 KiB

Open AccessArticle

Nondestructive Evaluation of Solids Based on Deformation Wave Theory

by Sanichiro Yoshida, Conor McGibboney and Tomohiro Sasaki

Appl. Sci. 2020, 10(16), 5524; https://doi.org/10.3390/app10165524 - 10 Aug 2020

Cited by 3 | Viewed by 2320

Abstract

The application of a recent field theory of deformation and fracture to nondestructive testing (NDT) is discussed. Based on the principle known as the symmetry of physical laws, the present field theory formulates all stages of deformation including the fracturing stage on the [...] Read more.

The application of a recent field theory of deformation and fracture to nondestructive testing (NDT) is discussed. Based on the principle known as the symmetry of physical laws, the present field theory formulates all stages of deformation including the fracturing stage on the same theoretical basis. The formalism derives wave equations that govern the spatiotemporal characteristics of the differential displacement field of solids under deformation. The evolution from the elastic to the plastic stage of deformation is characterized by a transition from longitudinal (compression) wave to decaying longitudinal/transverse wave characteristics. The evolution from the plastic to the fracturing stage is characterized by transition from continuous wave to solitary wave characteristics. Further, the evolution from the pre-fracturing to the final fracturing stage is characterized by transition from the traveling solitary wave to stationary solitary wave characteristics. In accordance with these transitions, the criterion for deformation stage is defined as specific spatiotemporal characteristics of the differential displacement field. The optical interferometric technique, known as Electronic Speckle-Pattern Interferometry (ESPI), is discussed as an experimental tool to visualize those wave characteristics and the associated deformation-stage criteria. The wave equations are numerically solved for the elastoplastic stages, and the resultant spatiotemporal behavior of the differential displacement field is compared with the experimental results obtained by ESPI. Agreement between the experimental and numerical results validates the present methodology at least for the elastoplastic stages. The solitary wave characteristics in the fracturing stages is discussed based on the experimental results and dislocation theory. Full article

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17 pages, 2327 KiB

Open AccessReview

Terahertz Inspection of Buildings and Architectural Art

by Kirsti Krügener, Jan Ornik, Lorentz M. Schneider, Alexander Jäckel, Corinna L. Koch-Dandolo, Enrique Castro-Camus, Nicole Riedl-Siedow, Martin Koch and Wolfgang Viöl

Appl. Sci. 2020, 10(15), 5166; https://doi.org/10.3390/app10155166 - 27 Jul 2020

Cited by 30 | Viewed by 4415

Abstract

We present a broad literature review on the uses of terahertz radiation for the inspection architectural art, as well as building structures. As an example of the uses of terahertz in this field, we also include original results on a non-destructive assessment of [...] Read more.

We present a broad literature review on the uses of terahertz radiation for the inspection architectural art, as well as building structures. As an example of the uses of terahertz in this field, we also include original results on a non-destructive assessment of a conservation intervention on murals of the Konstantinbasilika in Trier, Germany while using terahertz time-of-flight spectroscopy. Full article

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15 pages, 5836 KiB

Open AccessArticle

Digital Volume Correlation Applied to X-ray Micro-Tomography Images in Uniaxial Creep Tests on Anisotropic Clayey Rock

by Hailing Shi, Jerome Hosdez, Thomas Rougelot, Shouyi Xie, Jianfu Shao, Jean Talandier and Giuseppe Lacidogna

Appl. Sci. 2020, 10(14), 4898; https://doi.org/10.3390/app10144898 - 16 Jul 2020

Cited by 8 | Viewed by 2570

Abstract

Creep tests are commonly performed to characterize time-dependent deformation of geological materials. Classical measuring methods are not suitable for long term tests and not able to provide full three-dimensional strain fields. In this study, Digital Volume Correlation (DVC) is applied to X-ray micro-tomography [...] Read more.

Creep tests are commonly performed to characterize time-dependent deformation of geological materials. Classical measuring methods are not suitable for long term tests and not able to provide full three-dimensional strain fields. In this study, Digital Volume Correlation (DVC) is applied to X-ray micro-tomography (XRMT) images from creep tests on a hard clayey rock. In situ uniaxial compression creep tests are performed under different levels of stress and with different loading orientations with respect to the structural anisotropy of rock. Based on the XRMT images taken during the creep tests, DVC is applied to compute the full three dimensional strain fields and global averages strains of tested samples. The effects of bedding planes and hard inclusions on the non-uniform distribution of strains are analyzed. Full article

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33 pages, 19120 KiB

Open AccessArticle

Research on the Scope of Spectral Width Parameter of Frequency Domain Methods in Random Fatigue

by Jie Xu, Yaolei Zhang, Qinghua Han, Jia Li and Giuseppe Lacidogna

Appl. Sci. 2020, 10(14), 4715; https://doi.org/10.3390/app10144715 - 8 Jul 2020

Cited by 6 | Viewed by 2555

Abstract

In the current fatigue life calculation theory, the most commonly used method is the frequency domain method. However, most of the frequency domain fatigue life prediction models do not indicate the scope of the application of the spectral width parameter. Different frequency domain [...] Read more.

In the current fatigue life calculation theory, the most commonly used method is the frequency domain method. However, most of the frequency domain fatigue life prediction models do not indicate the scope of the application of the spectral width parameter. Different frequency domain methods have strict applicability to the spectral width parameter, and improper model selection will lead significant error. Therefore, it is particularly important to determine the scope of application of the spectral width parameter for different frequency-domain methods. This paper firstly introduces the current frequency domain methods, then simulates the analogue spectrum and selects three materials for comparison in the different frequency-domain methods. By analyzing and comparing the results of random fatigue life and relative error results, the application of different frequency-domain methods is obtained, and random vibration simulation verification is carried out with the practical engineering example, which can provide a reference for the selection of life prediction models. Full article

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26 pages, 6896 KiB

Open AccessArticle

The Elastic Wave Propagation in Rectangular Waveguide Structure: Determination of Dispersion Curves and Their Application in Nondestructive Techniques

by Eduardo Becker Groth, Thomas Gabriel Rosauro Clarke, Guilherme Schumacher da Silva, Ignacio Iturrioz and Giuseppe Lacidogna

Appl. Sci. 2020, 10(12), 4401; https://doi.org/10.3390/app10124401 - 26 Jun 2020

Cited by 15 | Viewed by 4914

Abstract

The use of mechanic waves for assessing structural integrity is a well-known non-destructive technique (NDT). The ultrasound applied in the guided wave in particular requires significant effort in order to understand the complexities of the propagation so as to develop new methods in [...] Read more.

The use of mechanic waves for assessing structural integrity is a well-known non-destructive technique (NDT). The ultrasound applied in the guided wave in particular requires significant effort in order to understand the complexities of the propagation so as to develop new methods in damage detection, in this case, knowing the interaction between the wave propagation and the geometry of the waveguides is mandatory. In the present work, the wave propagation in rectangular steel rod is presented. In this study, the section dimensions were fixed as 5 × 15 [mm], a typical element of the flexible riser structural amour commonly used in the offshore oil industry. The studies here presented were restricted to [0, 100 KHz] frequencies. This frequency interval is in the range of commercial waveguide equipment commonly applied in ducts in NDT applications. The computation of the dispersion curves is performed by using three different methodologies: (i) analytical solutions, (ii) a method that combines analytical approaches with finite element methods (SAFE), and (iii) experimental method that extracted information from the rod using laser vibrometers and piezoelectric actuators. Finally, two applications based on the dispersion curves determined in the rectangular waveguide are presented to illustrate the possibilities of the curve dispersion knowledge related to the specific geometry in the development and application linked to NDT. The first application consists on showing the possibilities of the techniques that use a fiber grating Bragg cell (FGB) to measure the wave displacement and the second application involves the simulation of pre-fissured prismatic waveguide aimed at searching to induce three characteristic acoustic events. The model was built combining the finite element method and a version of the discrete element method. Full article

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16 pages, 7505 KiB

Open AccessArticle

Electromagnetic Testing of Moisture Separation Reheater Tube based on Multivariate Singular Spectral Analysis

by Van Su Luong, Minhhuy Le, Khoa Dang Nguyen, Dang-Khanh Le and Jinyi Lee

Appl. Sci. 2020, 10(11), 3954; https://doi.org/10.3390/app10113954 - 6 Jun 2020

Cited by 1 | Viewed by 4035

Abstract

Moisture separator reheater (MSR) tubing systems are an important part of a pressurized-water power plant to increase the efficiency of the heat transfer rate. The MSR tubes are finned tubes which are made of ferritic stainless steel (SS439) with a high strength and [...] Read more.

Moisture separator reheater (MSR) tubing systems are an important part of a pressurized-water power plant to increase the efficiency of the heat transfer rate. The MSR tubes are finned tubes which are made of ferritic stainless steel (SS439) with a high strength and corrosion resistance characteristics. However, corrosion can appear along with the fins after a long period of operation of the MSR tubes that requires nondestructive testing (NDT) of the MSR tubes’ periodically. Electromagnetic testing (ET) is an efficient NDT method for the inspection of far-side corrosion in the MSR tubes. However, the ET sensor signal is affected by signal noise from the fins. Material degradation that make it challenging to inspect and evaluate the corrosion. In this study, we proposed three ET methods, including magnetic flux leakage testing, eddy current testing and partial saturation eddy current testing, and incorporated with a multivariate singular spectral analysis (MSSA) filter to improve the detectability of the corrosion in the MSR tubes. The proposed MSSA filter was compared with the multivariate wavelet transform filter and Gabor transform filter, and the results showed more efficient and stable results of the MSSA filter in the extraction of the corrosion signal. Full article

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23 pages, 5727 KiB

Open AccessArticle

Acoustic Emission Monitoring of the Turin Cathedral Bell Tower: Foreshock and Aftershock Discrimination

by Amedeo Manuello Bertetto, Davide Masera and Alberto Carpinteri

Appl. Sci. 2020, 10(11), 3931; https://doi.org/10.3390/app10113931 - 5 Jun 2020

Cited by 10 | Viewed by 3081

Abstract

Historical churches, tall ancient masonry buildings, and bell towers are structures subjected to high risks due to their age, elevation, and small base-area-to-height ratio. In this paper, the results of an innovative monitoring technique for structural integrity assessment applied to a historical bell [...] Read more.

Historical churches, tall ancient masonry buildings, and bell towers are structures subjected to high risks due to their age, elevation, and small base-area-to-height ratio. In this paper, the results of an innovative monitoring technique for structural integrity assessment applied to a historical bell tower are reported. The emblematic case study of the monitoring of the Turin Cathedral bell tower (northwest Italy) is herein presented. First of all, the damage evolution in a portion of the structure localized in the lower levels of the tall masonry building is described by the evaluation of the cumulative number of acoustic emissions (AEs) and by different parameters able to predict the time dependence of the damage development, in addition to the 3D localization of the AE sources. The b-value analysis shows a decreasing trend down to values compatible with the growth of localized micro and macro-cracks in the portion of the structure close to the base of the tower. These results seem to be in good agreement with the static and dynamic analysis performed numerically by an accurate FEM (finite element model). Similar results were also obtained during the application of the AE monitoring to the wooden frame sustaining the bells in the tower cell. Finally, a statistical analysis based on the average values of the b-value are carried out at the scale of the monument and at the seismic regional scale. In particular, according to recent studies, a comparison between the b-value obtained by AE signal analysis and the regional activity is proposed in order to correlate the AE detected on the structure to the seismic activity, discriminating foreshock, and aftershock intervals in the analyzed time series. Full article

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15 pages, 3882 KiB

Open AccessArticle

Identification of Deformation Stage and Crack Initiation in TC11 Alloys Using Acoustic Emission

by Jiaoyan Huang, Zhiheng Zhang, Cong Han and Guoan Yang

Appl. Sci. 2020, 10(11), 3674; https://doi.org/10.3390/app10113674 - 26 May 2020

Cited by 7 | Viewed by 2480

Abstract

The Acoustic Emission (AE) is a widely used real-time monitoring technique for the deformation damage and crack initiation of areo-engine blades. In this work, a tensile test for TC11 titanium alloy, one of the main materials of aero-engine, was performed. The AE signals [...] Read more.

The Acoustic Emission (AE) is a widely used real-time monitoring technique for the deformation damage and crack initiation of areo-engine blades. In this work, a tensile test for TC11 titanium alloy, one of the main materials of aero-engine, was performed. The AE signals from different stages of this test were collected. Then, the AE signals were decomposed by the Variational Mode Decomposition (VMD) method, in which the signals were divided into two different frequency bands. We calculated the engery ratio by dividing the two different frequency bands to characterize TC11′s degree of deformation. The results showed that when the energy ratio was −0.5 dB, four stages of deformation damage of the TC11 titanium alloy could be clearly identified. We further combined the calculated Partial Energy Ratio (PER) and Weighted Peak Frequency (WPF) to identify the crack initiation of the TC11 titanium alloy. The results showed that the identification accuracy was 96.33%. Full article

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16 pages, 4317 KiB

Open AccessArticle

Nondestructive Monitoring Techniques for Crack Detection and Localization in RC Elements

by Marco Domaneschi, Gianni Niccolini, Giuseppe Lacidogna and Gian Paolo Cimellaro

Appl. Sci. 2020, 10(9), 3248; https://doi.org/10.3390/app10093248 - 7 May 2020

Cited by 27 | Viewed by 3513

Abstract

This paper presents the structural and damage assessment of a reinforced concrete (RC) beam subjected to a four-point bending test until yielding of reinforcing steel. The deterioration progress was monitored using different nondestructive testing (NDT) techniques. The strain was measured by distributed fiber [...] Read more.

This paper presents the structural and damage assessment of a reinforced concrete (RC) beam subjected to a four-point bending test until yielding of reinforcing steel. The deterioration progress was monitored using different nondestructive testing (NDT) techniques. The strain was measured by distributed fiber optic sensors (FOSs), embedded prior to concrete pouring. The initiation and propagation of cracks were monitored by acoustic emission (AE) sensors attached to the surface of the material. The recorded AE activity results in good agreement with FOS strain measurements. The results of the integrated monitoring system are confirmed by visual observation of the actual crack pattern. At different loading steps, digital image correlation (DIC) analysis was also conducted. Full article

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16 pages, 8894 KiB

Open AccessArticle

Application of Impact-Echo Method to 3D SIBIE Procedure for Damage Detection in Concrete

by Katsufumi Hashimoto, Tomoki Shiotani and Masayasu Ohtsu

Appl. Sci. 2020, 10(8), 2729; https://doi.org/10.3390/app10082729 - 15 Apr 2020

Cited by 7 | Viewed by 3401

Abstract

In this study, to visualize damage and defects, such as cracks and voids in concrete, the SIBIE (stack imaging of spectral amplitudes based on impact echo) procedure is applied and numerically improved to construct a three-dimensional (3D) model of elastic wave propagation behavior. [...] Read more.

In this study, to visualize damage and defects, such as cracks and voids in concrete, the SIBIE (stack imaging of spectral amplitudes based on impact echo) procedure is applied and numerically improved to construct a three-dimensional (3D) model of elastic wave propagation behavior. A unit of arrayed accelerometers is installed to detect multi-channel signal waveforms in the frequency domain. The resonant frequencies due to reflections at each node in 3D lattice nodes are computed by using the distances from elastic wave input to multiple output locations. The amplitudes corresponding to the resonant frequencies in the spectrum are summed up as the reflection intensity of elastic wave at each node. The reflection intensity distribution is visualized finally in the targeted area three-dimensionally. Case studies are carried out on the proposal of the improved 3D-SIBIE procedure, applied to a concrete specimen with simulated-damage as well as in-situ highway RC (Reinforced Concrete) slabs in service. As for the signal detection, a non-contact elastic wave detecting system using a laser doppler vibrometer is also introduced to consider and validate the promising remote sensing and inspection technique for damage evaluation in concrete with the 3D SIBIE procedure. Full article

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15 pages, 5962 KiB

Open AccessArticle

Non-Destructive Tests for Damage Evaluation of Stone Columns: The Case Study of Sacro Monte in Ghiffa (Italy)

by Alessandro Grazzini, Sara Fasana, Marco Zerbinatti and Giuseppe Lacidogna

Appl. Sci. 2020, 10(8), 2673; https://doi.org/10.3390/app10082673 - 13 Apr 2020

Cited by 7 | Viewed by 2768

Abstract

The Italian Sacri Monti are heritage sites with some unique characteristics; they are a successful symbiosis between nature and art and are unconfined structures, therefore always being accessible but exposed to atmospheric agents, with many relevant consequences with regard to conservation problems. The [...] Read more.

The Italian Sacri Monti are heritage sites with some unique characteristics; they are a successful symbiosis between nature and art and are unconfined structures, therefore always being accessible but exposed to atmospheric agents, with many relevant consequences with regard to conservation problems. The paper discusses some aspects related to the application of non-destructive techniques (NDT) for the interpretation of degradation phenomena occurring in stone structural elements. Ultrasonic and impact tests were used to evaluate the structural properties of the stone columns in the Via Crucis portico, within the monumental complex of the Sacro Monte in Ghiffa (Piedmont, Italy), in order to determine their conditions of maintenance and to evaluate the portico static stability. Ultrasonic tests made it possible to obtain the value of the dynamic elastic modulus, which was variable at different points of the columns due to the diversified level of material damage. The impact test, performed with an instrumented hammer in the same points of the ultrasonic test, enables, by comparison, a deeper knowledge of the surface resistance of damaged columns. These results are the first step in a research path that will require further laboratory tests to better calibrate the diagnostic techniques applied to different levels of damage to surface materials. Full article

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24 pages, 10685 KiB

Open AccessArticle

Non-Invasive Identification of Vulnerability Elements in Existing Buildings and Their Visualization in the BIM Model for Better Project Management: The Case Study of Cuccagna Farmhouse

by Elsa Garavaglia, Anna Anzani, Fabio Maroldi and Fabio Vanerio

Appl. Sci. 2020, 10(6), 2119; https://doi.org/10.3390/app10062119 - 20 Mar 2020

Cited by 12 | Viewed by 2870

Abstract

Due to the conjunction between the European and African plates, complex tectonic phenomena take place in the Mediterranean basin. These phenomena cause more or less violent seismic resentments in the countries facing the basin itself. The diffused built historical heritage, characteristic of villages [...] Read more.

Due to the conjunction between the European and African plates, complex tectonic phenomena take place in the Mediterranean basin. These phenomena cause more or less violent seismic resentments in the countries facing the basin itself. The diffused built historical heritage, characteristic of villages in the Mediterranean countries, is the most vulnerable toward seismic action, and in case of a catastrophic event can cause the loss of human lives. In Italy, the protection of historic buildings is a significant issue, and many regions promoted policies to ensure the safety of the diffused built heritage. Research groups work in synergy to develop procedures for the vulnerability assessment of existing buildings and to define appropriate action plans. This research presents a little or not at all invasive procedure for investigating vulnerability. This procedure is easily replicable and able to support techniques already in use with innovative aspects such as laser scanning of the entire complex and visual identification of vulnerable elements through the BIM (building information modeling) methodology. The procedure applicability is shown in the study of a Milanese farmhouse that has been financed by Fondazione CARIPLO, Bandi 2017 Arte e Cultura-Beni culturali a rischio, Project PRE.CU.R.S.OR. Full article

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17 pages, 3374 KiB

Open AccessArticle

Simulation of Three Constitutive Behaviors Based on Nonlinear Ultrasound

by Zaifu Zhan, Shen Wang, Fuping Wang, Songling Huang, Wei Zhao and Zhe Wang

Appl. Sci. 2020, 10(6), 1982; https://doi.org/10.3390/app10061982 - 13 Mar 2020

Cited by 4 | Viewed by 2091

Abstract

Nonlinear ultrasound has attracted more and more attention. In classical acoustic nonlinear theory, the source of nonlinearity is the change of constitutive relation of materials. Structure response that distorts after a single tone ultrasound wave is important to detect imperfection. This is rarely [...] Read more.

Nonlinear ultrasound has attracted more and more attention. In classical acoustic nonlinear theory, the source of nonlinearity is the change of constitutive relation of materials. Structure response that distorts after a single tone ultrasound wave is important to detect imperfection. This is rarely found in current simulations. The current simulation always introduces defects which do not match to the classical acoustic nonlinear theory. In this manuscript, the recurrence expressions of three kinds of imperfect materials for subroutine are given. The verifying simulation model that is used for verifying recurrence equations and wave propagation model that are used for analysing the process of ultrasonic propagation are established. The results show that the two constitutive models are effective in the verifying simulation and the hysteresis material has some special characteristics. Finally, ultrasonic propagation in two types of materials produce the expected harmonics, which build foundations for simulations of nonlinear ultrasound. Full article

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14 pages, 2913 KiB

Open AccessArticle

Bonding Characteristics of Single- and Joggled-Lap CFRP Specimens: Mechanical and Acoustic Investigations

by Claudia Barile, Caterina Casavola, Vincenzo Moramarco, Carmine Pappalettere and Paramsamy Kannan Vimalathithan

Appl. Sci. 2020, 10(5), 1782; https://doi.org/10.3390/app10051782 - 5 Mar 2020

Cited by 12 | Viewed by 3881

Abstract

Two different configurations of adhesive-bonded carbon fiber-reinforced plastic (CFRP) specimens, joggled lap-joint specimens and single lap-joint specimens, are mechanically tested. The mechanical tests show that the joggled lap specimens have lower strength than the single lap specimens. The damage modes in both the [...] Read more.

Two different configurations of adhesive-bonded carbon fiber-reinforced plastic (CFRP) specimens, joggled lap-joint specimens and single lap-joint specimens, are mechanically tested. The mechanical tests show that the joggled lap specimens have lower strength than the single lap specimens. The damage modes in both the specimens are analysed by the Acoustic Emission descriptors recorded during the mechanical tests. The acoustic data as cumulative counts and cumulative energy show the critical points of failure in both the specimen groups under loading. Moreover, they also show that the damage modes in both the specimens are dissimilar. Finally, the data provided by acoustic emission descriptors are verified by fractographic analysis on the failed surface. Full article

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16 pages, 2894 KiB

Open AccessReview

Mechanical Strength Evaluation of Elastic Materials by Multiphysical Nondestructive Methods: A Review

by Huiting Huan, Lixian Liu, Andreas Mandelis, Cuiling Peng, Xiaolong Chen and Jinsong Zhan

Appl. Sci. 2020, 10(5), 1588; https://doi.org/10.3390/app10051588 - 27 Feb 2020

Cited by 11 | Viewed by 4098

Abstract

The main purpose of industrial nondestructive testing (NDT) is to diagnose the stability, reliability and failure probability of materials, components and structures. Industrial component mechanical strength is one of the most important properties NDT is used to characterize. Subtle but perceptible changes in [...] Read more.

The main purpose of industrial nondestructive testing (NDT) is to diagnose the stability, reliability and failure probability of materials, components and structures. Industrial component mechanical strength is one of the most important properties NDT is used to characterize. Subtle but perceptible changes in stress-strain behavior can be reliable indicators of defect formation. A detailed review on the state-of-the-art NDT methods using optical-radiation, photoacoustic, and photothermal techniques for mechanical strength evaluation and defect pre-diagnosis is presented in this article. Mechanical strength is analyzed in terms of the deformation/strain field, the stress-strain relation, and the residual stress in an elastic material subjected to tensile or compressive loading, or impact. By introducing typical NDT experiments, the history and features of each methodology are revisited and typical applications are discussed. This review also aims to be used as a reference toward further research and development of NDT technologies characterizing mechanical strength of materials and components. Full article

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16 pages, 3642 KiB

Open AccessFeature PaperArticle

Inducing Damage Diagnosis Capabilities in Carbon Fiber Reinforced Polymer Composites by Magnetoelastic Sensor Integration via 3D Printing

by Dimitrios G. Dimogianopoulos, Panagiotis J. Charitidis and Dionysios E. Mouzakis

Appl. Sci. 2020, 10(3), 1029; https://doi.org/10.3390/app10031029 - 4 Feb 2020

Cited by 8 | Viewed by 3312

Abstract

This study investigates the possibility of inducing damage diagnosis capabilities in carbon fiber reinforced polymer composite slabs using custom-built integrated sensors and conventional, affordable equipment. The concept utilizes magnetoelastic strips integrated via 3D printing procedures in composite slabs. Under external mechanical loading, the [...] Read more.

This study investigates the possibility of inducing damage diagnosis capabilities in carbon fiber reinforced polymer composite slabs using custom-built integrated sensors and conventional, affordable equipment. The concept utilizes magnetoelastic strips integrated via 3D printing procedures in composite slabs. Under external mechanical loading, the strip magnetization changes due to the magnetoelastic phenomenon. Accordingly, electrical signals may be passively induced in conventional reception coil circuits placed at a distance from the slab. Since these signals quantify the vibrating slab’s response, which is affected by the slab’s structural integrity, damage may be detected when specific signal characteristics change. Two main issues are examined, namely the ability of receiving meaningful (with respect to noise) electrical signals from the built-in strips despite their contact-less passive reception, and the potential of diagnosing damage using such signals. Hence, slabs of various sizes and levels of structural damage (notches) have been vibrated at different frequencies and amplitudes. Treating the experimental data from integrated strips by applying the proposed processing framework allows for calculating eigenfrequencies sensitive to occurring damage (and its severity), as verified by finite element models of the vibrating slabs. Accordingly, damage may be detected and evaluated via the currently proposed experimental testing and analysis framework. Full article

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2019

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15 pages, 6385 KiB

Open AccessArticle

Stress Estimation Using the Acoustoelastic Effect of Surface Waves in Weak Anisotropic Materials

by Jihyun Jun, Young-Dae Shim and Kyung-Young Jhang

Appl. Sci. 2020, 10(1), 169; https://doi.org/10.3390/app10010169 - 24 Dec 2019

Cited by 4 | Viewed by 3229

Abstract

This paper proposes a novel stress measurement method using the acoustoelastic effect of surface wave to estimate the stress of a homogeneous material plate with orthogonal anisotropy, in which the surface wave velocities are measured in three different directions before and after loading [...] Read more.

This paper proposes a novel stress measurement method using the acoustoelastic effect of surface wave to estimate the stress of a homogeneous material plate with orthogonal anisotropy, in which the surface wave velocities are measured in three different directions before and after loading stress. The effectiveness of the proposed method was verified by numerical simulations and experiments. For the simulations, the surface wave velocities in three directions were obtained from a conventional perturbation model for weak anisotropic materials. The simulation results showed that the stress estimation error was less than 3% for an anisotropic rate up to 2% under stress conditions up to 90 MPa. Two specimens were prepared for the experiments, one was almost isotropic and another that had a relatively larger anisotropy rate of 2.6%. Then, the stresses loaded by a tensile test machine were estimated. The results showed good agreement with the given stresses for both specimens. These results confirm that the proposed method can be applied to estimate the surface stress state in anisotropic material plates. The proposed method is simple, practical, and is expected to be useful for monitoring changes of surface stress before and after machining such as the punching or bending of plate. Full article

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11 pages, 1308 KiB

Open AccessArticle

Using Acoustic Emission Measurements for Ice-Melting Detection

by Michael Stamm, Helge Pfeiffer, Johan Reynaert and Martine Wevers

Appl. Sci. 2019, 9(24), 5387; https://doi.org/10.3390/app9245387 - 9 Dec 2019

Cited by 8 | Viewed by 3353

Abstract

Aircraft operators being faced with water accumulation in fuel tanks on a daily basis and are looking for reliable detection systems to determine the remaining amount of accumulated ice during maintenance after flight. Using such a technology, an increase in the safety and [...] Read more.

Aircraft operators being faced with water accumulation in fuel tanks on a daily basis and are looking for reliable detection systems to determine the remaining amount of accumulated ice during maintenance after flight. Using such a technology, an increase in the safety and efficiency of the aircraft operation would be possible in this highly competitive market. This article presents the use of the Acoustic Emission Technique (AE) for the reliable and non-invasive monitoring of the melting of ice in fuel tanks. This technology is in principle based on the fact that a phase transition comes frequently along with stress relaxation that can be used for monitoring the process. Therefore, the melting of water can, in essence, be monitored with AE without accessing the ice directly. The analysis of the AE signals has been carried out in the time domain since it was the melting of ice needed to be monitored as a function of temperature rise time. The insights presented in this paper can possibly lead to new technologies for ice detection, especially in remote areas that are not easily accessible with other techniques. Full article

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28 pages, 4846 KiB

Open AccessFeature PaperArticle

The Teager-Kaiser Energy Cepstral Coefficients as an Effective Structural Health Monitoring Tool

by Marco Civera, Matteo Ferraris, Rosario Ceravolo, Cecilia Surace and Raimondo Betti

Appl. Sci. 2019, 9(23), 5064; https://doi.org/10.3390/app9235064 - 23 Nov 2019

Cited by 30 | Viewed by 3399

Abstract

Recently, features and techniques from speech processing have started to gain increasing attention in the Structural Health Monitoring (SHM) community, in the context of vibration analysis. In particular, the Cepstral Coefficients (CCs) proved to be apt in discerning the response of a damaged [...] Read more.

Recently, features and techniques from speech processing have started to gain increasing attention in the Structural Health Monitoring (SHM) community, in the context of vibration analysis. In particular, the Cepstral Coefficients (CCs) proved to be apt in discerning the response of a damaged structure with respect to a given undamaged baseline. Previous works relied on the Mel-Frequency Cepstral Coefficients (MFCCs). This approach, while efficient and still very common in applications, such as speech and speaker recognition, has been followed by other more advanced and competitive techniques for the same aims. The Teager-Kaiser Energy Cepstral Coefficients (TECCs) is one of these alternatives. These features are very closely related to MFCCs, but provide interesting and useful additional values, such as e.g., improved robustness with respect to noise. The goal of this paper is to introduce the use of TECCs for damage detection purposes, by highlighting their competitiveness with closely related features. Promising results from both numerical and experimental data were obtained. Full article

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15 pages, 2233 KiB

Open AccessArticle

The Rapid Detection Technology of Lamb Wave for Microcracks in Thin-Walled Tubes

by Shunmin Yang, Mingquan Wang and Lu Yang

Appl. Sci. 2019, 9(17), 3576; https://doi.org/10.3390/app9173576 - 1 Sep 2019

Cited by 3 | Viewed by 2698

Abstract

Thin-walled tubes are a kind of pressure vessel formed by a stamping and drawing process, which must withstand a great deal of sudden pressure during use. When microcrack defects of a certain depth are present on its inner and outer surfaces, severe safety [...] Read more.

Thin-walled tubes are a kind of pressure vessel formed by a stamping and drawing process, which must withstand a great deal of sudden pressure during use. When microcrack defects of a certain depth are present on its inner and outer surfaces, severe safety accidents may occur, such as cracking and crushing. Therefore, it is necessary to carry out nondestructive testing of thin-walled tubes in the production process to eliminate the potential safety hazards. To realize the rapid detection of microcracks in thin-walled tubes, this study could be summarized as follows: (i) Because the diameters of the thin-walled tubes were much larger than their thicknesses, Lamb wave characteristics of plates with equal thicknesses were used to approximate the dispersion characteristics of thin-walled tubes. (ii) To study the dispersion characteristics of Lamb waves in thin plates, the detection method of the

A_{0}

mode was determined using the particle displacement–amplitude curve. (iii) Using a multi-channel parallel detection method, rapid detection equipment for Lamb wave microcracks in thin-walled tubes was developed. (iv) The filtering peak values for defect signal detection with different depths showed that the defect detection peak values could reflect the defect depth information. (v) According to the minimum defect standard of a 0.045-mm depth, 100,000 thin-walled tubes were tested. The results showed that the missed detection rate was 0%, the reject rate was 0.3%, and the detection speed was 5.8 s/piece, which fully meets the actual detection requirements of production lines. Therefore, this study not only solved the practical issues for the rapid detection of microcracks in thin-walled tubes but also provided a reference for the application of ultrasonic technology for the detection of other components. Full article

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14 pages, 5678 KiB

Open AccessArticle

A Deep Learning Based Method for the Non-Destructive Measuring of Rock Strength through Hammering Sound

by Shuai Han, Heng Li, Mingchao Li and Timothy Rose

Appl. Sci. 2019, 9(17), 3484; https://doi.org/10.3390/app9173484 - 23 Aug 2019

Cited by 13 | Viewed by 3157

Abstract

Hammering rocks of different strengths can make different sounds. Geological engineers often use this method to approximate the strengths of rocks in geology surveys. This method is quick and convenient but subjective. Inspired by this problem, we present a new, non-destructive method for [...] Read more.

Hammering rocks of different strengths can make different sounds. Geological engineers often use this method to approximate the strengths of rocks in geology surveys. This method is quick and convenient but subjective. Inspired by this problem, we present a new, non-destructive method for measuring the surface strengths of rocks based on deep neural network (DNN) and spectrogram analysis. All the hammering sounds are transformed into spectrograms firstly, and a clustering algorithm is presented to filter out the outliers of the spectrograms automatically. One of the most advanced image classification DNN, the Inception-ResNet-v2, is then re-trained with the spectrograms. The results show that the training accurate is up to 94.5%. Following this, three regression algorithms, including Support Vector Machine (SVM), K-Nearest Neighbor (KNN), and Random Forest (RF) are adopted to fit the relationship between the outputs of the DNN and the strength values. The tests show that KNN has the highest fitting accuracy, and SVM has the strongest generalization ability. The strengths (represented by rebound values) of almost all the samples can be predicted within an error of [−5, 5]. Overall, the proposed method has great potential in supporting the implementation of efficient rock strength measurement methods in the field. Full article

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18 pages, 8508 KiB

Open AccessArticle

Detecting the Void behind the Tunnel Lining by Impact-Echo Methods with Different Signal Analysis Approaches

by Rongning Cao, Meng Ma, Ruihua Liang and Chao Niu

Appl. Sci. 2019, 9(16), 3280; https://doi.org/10.3390/app9163280 - 10 Aug 2019

Cited by 17 | Viewed by 4193

Abstract

A void behind the lining in a tunnel is considered to be a critical condition as it can significantly impair the tunnel service life. In this study, we adopted the impact-echo (IE) method to detect the voids. We designed two test conditions (tunnel [...] Read more.

A void behind the lining in a tunnel is considered to be a critical condition as it can significantly impair the tunnel service life. In this study, we adopted the impact-echo (IE) method to detect the voids. We designed two test conditions (tunnel lining with and without a void) for our experiments performed in a laboratory environment. The influences of void size and impact-void position were analysed using numerical simulations. The vibration response signals were analysed in the time, frequency, and time–frequency domains using various signal analysis approaches. The results were comparatively analysed to determine the best approach for void detection. The study helped establish that a tunnel void can be evaluated through the vibration energy (amplitude and duration) in the time domain, the resonance frequency and dynamic stiffness in the frequency domain, and the energy distribution in time–frequency domain. The wavelet transform analysis is the most appropriate method to observe the energy flow during the state changing and the dynamic stiffness method can determine the void position precisely. Full article

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14 pages, 5195 KiB

Open AccessArticle

A PEC Thrice Subtraction Method for Obtaining Permeability Invariance Feature in Conductivity Measurement of Ferromagnetic Samples

by Dongdong Wen, Mengbao Fan, Binghua Cao, Zhian Xue and Ping Wang

Appl. Sci. 2019, 9(13), 2745; https://doi.org/10.3390/app9132745 - 7 Jul 2019

Cited by 8 | Viewed by 3389

Abstract

Conductivity, as an important index of structural health monitoring, can be used to evaluate heat treatment condition, and sort different materials or measure the stress of mechanical parts. However, the permeability of a measured sample has significant impact on the detected signal in [...] Read more.

Conductivity, as an important index of structural health monitoring, can be used to evaluate heat treatment condition, and sort different materials or measure the stress of mechanical parts. However, the permeability of a measured sample has significant impact on the detected signal in pulsed eddy current (PEC) testing, which is prone to measurement errors due to the effect of permeability change. In this paper, a thrice subtraction method is investigated and utilized to obtain a permeability invariance (PI) feature for reducing permeability effect in conductivity measurement of ferromagnetic samples. The thrice subtraction method is based on the PEC signals of sample and air, the difference signal between the difference PEC signal and its normalization signal, and the difference signal between the difference normalization signal and its standard deviation. In the thrice subtraction signals, the behavior of the obtained PI feature is analyzed by experiments and simulations. The results demonstrate that the thrice subtraction method is a practicable program and the PI feature is potential to measure the conductivity of ferromagnetic samples. The work reported in this paper provides an effective approach to obtain a PI feature for estimating the conductivity of ferromagnetic samples without a permeability effect. Full article

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