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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Materials Simulation and Design".

Deadline for manuscript submissions: closed (31 July 2021) | Viewed by 44287

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Dr. Claudia Barile

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Dipartimento di Meccanica, Matematica e Management, Politecnico di Bari, Via Orabona 4, 70125 Bari, Italy
Interests: experimental mechanics; mechanical testing; materials behavior; acoustic emission; CFRP; structural health monitoring; nondestructive evaluation
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Dear Colleagues,

The increasing use of properly designed materials for specific applications has led to the widespread use of composite materials. Composites reveal a mechanical behavior deeply different from that of conventional materials, such as metals, owing to their nature. More specifically, the considerable performance demands of some structural applications require the use of high resistance carbon fiber reinforced plastics (CFRP). Lightweight composite structures are being used in an ever-increasing variety of products and applications, such as aerospace, ground transportation, and environmentally sustainable energy systems. For a complete knowledge of their performances, composite structures and components need mechanical and physical testing prior to their applications. Thus, the full characterization of the properties of anisotropic and inhomogeneous composite materials, for use in demanding structural applications, requires a wide range of mechanical tests, as well as numerical modeling, in order to have a precise idea of their mechanical behavior.

This Special Issue will focus on mechanical characterization with both traditional and innovative techniques of CRFP materials produced using different kinds of manufacturing processes, and on their numerical and analytical models. Special attention will be given to innovative approaches for predicting mechanical responses during work conditions.

Prof. Dr. Claudia Barile
Guest Editor

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Keywords

Mechanical characterization of CFRP
Numerical model of CFRP
Delamination
Fibers orientation
Stitching process
Damage mechanism
Mechanical behavior

Published Papers (13 papers)

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Research

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17 pages, 8553 KiB

Open AccessArticle

Finite Element Analysis of Lightning Damage Factors Based on Carbon Fiber Reinforced Polymer

by Yansong Zhu, Yueke Ming, Ben Wang, Yugang Duan, Hong Xiao, Chenping Zhang, Jinru Sun and Xiangyu Tian

Materials 2021, 14(18), 5210; https://doi.org/10.3390/ma14185210 - 10 Sep 2021

Cited by 4 | Viewed by 1887

Abstract

While carbon-fiber-reinforced polymers (CFRPs) are widely used in the aerospace industry, they are not able to disperse current from lightning strikes because their conductivity is relatively low compared to metallic materials. As such, the undispersed current can cause the vaporization or delamination of the composites, threatening aircraft safety. In this paper, finite element models of lightning damage to CFRPs were established using commercial finite element analysis software, Abaqus, with the user-defined subroutines USDFLD and HEAVEL. The influences of factors such as the structural geometry, laminate sequence, and intrinsic properties of CFRPs on the degree of damage to the composites are further discussed. The results showed that when a current from lightning is applied to the CFRP surface, it mainly disperses along the fiber direction in the outermost layer. As the length of the CFRP increases, the injected current has a longer residence time in the material due to the increased current exporting distance. Consequently, larger amounts of current accumulate on the surface, eventually leading to more severe damage to the CFRP. This damage can be alleviated by increasing the thickness of the CFRP, as the greater overall resistance makes the CFRP a better insulator against the imposed current. This study also found that the damaged area increased as the angle between the first two layers increased, whereas the depth of the damage decreased due to the current dispersion between the first two layers. The analysis of the electrical conductivity of the composite suggested that damage in the fiber direction will be markedly reduced if the conductivity in the vertical fiber direction increases approximately up to the conductivity of the fiber direction. Moreover, increasing the thermal conductivity along the fiber direction will accelerate the heat dissipation process after the lightning strike, but the influence of the improved thermal conductivity on the extent of the lightning damage is less significant than that of the electrical conductivity. Full article

(This article belongs to the Special Issue Carbon Fibre Reinforced Plastics)

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17 pages, 475 KiB

Open AccessArticle

Residually Stressed Fiber Reinforced Solids: A Spectral Approach

by Mohd Halim Bin Mohd Shariff and Jose Merodio

Materials 2020, 13(18), 4076; https://doi.org/10.3390/ma13184076 - 14 Sep 2020

Cited by 13 | Viewed by 1888

Abstract

We use a spectral approach to model residually stressed elastic solids that can be applied to carbon fiber reinforced solids with a preferred direction; since the spectral formulation is more general than the classical-invariant formulation, it facilitates the search for an adequate constitutive equation for these solids. The constitutive equation is governed by spectral invariants, where each of them has a direct meaning, and are functions of the preferred direction, the residual stress tensor and the right stretch tensor. Invariants that have a transparent interpretation are useful in assisting the construction of a stringent experiment to seek a specific form of strain energy function. A separable nonlinear (finite strain) strain energy function containing single-variable functions is postulated and the associated infinitesimal strain energy function is straightforwardly obtained from its finite strain counterpart. We prove that only 11 invariants are independent. Some illustrative boundary value calculations are given. The proposed strain energy function can be simply transformed to admit the mechanical influence of compressed fibers to be partially or fully excluded. Full article

(This article belongs to the Special Issue Carbon Fibre Reinforced Plastics)

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16 pages, 5168 KiB

Open AccessArticle

Study on the Flexural Performance of Hybrid-Reinforced Concrete Beams with a New Cathodic Protection System Subjected to Corrosion

by Yingwu Zhou, Yaowei Zheng, Lili Sui, Biao Hu and Xiaoxu Huang

Materials 2020, 13(1), 234; https://doi.org/10.3390/ma13010234 - 5 Jan 2020

Cited by 16 | Viewed by 3231

Abstract

Steel corrosion is considered as the main factor for the insufficient durability of concrete structures, especially in the marine environment. In this paper, to further inhibit steel corrosion in a high chloride environment and take advantage of the dual-functional carbon fiber reinforced polymer (CFRP), the impressed current cathodic protection (ICCP) technique was applied to the hybrid-reinforced concrete beam with internally embedded CFRP bars and steel fiber reinforced polymer composite bar (SFCB) as the anode material while the steel bar was compelled to the cathode. The effect of the new ICCP system on the flexural performance of the hybrid-reinforced concrete beam subjected to corrosion was verified experimentally. First, the electricity-accelerated precorrosion test was performed for the steel bar in the hybrid-reinforced beams with a target corrosion ratio of 5%. Then, the dry–wet cycles corrosion was conducted and the ICCP system was activated simultaneously for the hybrid-reinforced concrete beam for 180 days. Finally, the three-point bending experiment was carried out for the hybrid-reinforced concrete beams. The steel bars were taken out from the concrete to quantitatively measure the corrosion ratio after flexural tests. Results showed that the further corrosion of steel bars could be inhibited effectively by the ICCP treatment with the CFRP bar and the SFCB as the anode. Additionally, the ICCP system showed an obvious effect on the flexural behavior of the hybrid-reinforced concrete beams: The crack load and ultimate load, as well as the stiffness, were enhanced notably compared with the beam without ICCP treatment. Compared with the SFCB anode, the ICCP system with the CFRP bar as the anode material was more effective for the hybrid-reinforced concrete beam to prevent the steel corrosion. Full article

(This article belongs to the Special Issue Carbon Fibre Reinforced Plastics)

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13 pages, 2316 KiB

Open AccessArticle

A New Cutting Device Design to Study the Orthogonal Cutting of CFRP Laminates at Different Cutting Speeds

by Víctor Criado, Norberto Feito, José Luis Cantero Guisández and José Díaz-Álvarez

Materials 2019, 12(24), 4074; https://doi.org/10.3390/ma12244074 - 6 Dec 2019

Cited by 9 | Viewed by 2242

Abstract

Carbon Fiber-reinforced plastics (CFRPs) are widely used in the aerospace industry due to their highly mechanical properties and low density. Most of these materials are used in high-risk structures, where the damage caused by machining must be controlled and minimized. The optimization of these processes is still a challenge in the industry. In this work, a special cutting device, which allows for orthogonal cutting tests, with a linear displacement at a wide range of constant cutting speeds, has been developed by the authors. This paper describes the developed cutting device and its application to analyze the influence of tool geometry and cutting parameters on the material damage caused by the orthogonal cutting of a thick multidirectional CFRP laminate. The results show that a more robust geometry (higher cutting edge radius and lower rake angle) and higher feed cause an increase in the thrust force of a cutting tool, causing burrs and delamination damage. By reducing the cutting speed, the components with a higher machining force were also observed to have less surface integrity control. Full article

(This article belongs to the Special Issue Carbon Fibre Reinforced Plastics)

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14 pages, 6985 KiB

Open AccessArticle

Fiber Bridging Induced Toughening Effects on the Delamination Behavior of Composite Stiffened Panels under Bending Loading: A Numerical/Experimental Study

by Angela Russo, Mauro Zarrelli, Andrea Sellitto and Aniello Riccio

Materials 2019, 12(15), 2407; https://doi.org/10.3390/ma12152407 - 28 Jul 2019

Cited by 21 | Viewed by 2779

Abstract

In this paper, a research activity, focused on the investigation of new reinforcements able to improve the toughness of composite materials systems, is introduced. The overall aim is to delay the delamination propagation and, consequently, to increase the carrying load capability of composite structures by exploiting the fiber bridging effects. Indeed, the influence of fiber bridging related Mode I fracture toughness (G_Ic) values on the onset and propagation of delaminations in stiffened composite panels, under three-point bending loading conditions, have been experimentally and numerically studied. The investigated stiffened panels have been manufactured by using epoxy resin/carbon fibers material systems, characterized by different G_Ic values, which can be associated with the material fiber bridging sensitivity. Experimental data, in terms of load and delaminated area as a function of the out-of-plane displacements, have been obtained for each tested sample. Non-Destructive Inspection (NDI) has been performed to identify the debonding extension and position. To completely understand the evolution of the delamination and its dependence on the material characteristics, experiments have been numerically simulated using a newly developed robust numerical procedure for the delamination growth simulation, able to take into account the influence of the fracture toughness changes, associated with the materials’ fiber bridging sensitivity. The combined use of numerical results and experimental data has allowed introducing interesting considerations of the capability of the fiber bridging to substantially slow down the evolution of the debonding between skin and reinforcements in composite stiffened panels. Full article

(This article belongs to the Special Issue Carbon Fibre Reinforced Plastics)

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10 pages, 2412 KiB

Open AccessArticle

Study on Tensile Properties of CFRP Plates under Elevated Temperature Exposure

by Yongxin Yang, Yanju Jiang, Hongjun Liang, Xiaosan Yin and Yue Huang

Materials 2019, 12(12), 1995; https://doi.org/10.3390/ma12121995 - 21 Jun 2019

Cited by 14 | Viewed by 3785

Abstract

Elevated temperature exposure has a negative effect on the performance of the matrix resin in Carbon Fiber Reinforced Plastics (CFRP) plates, whereas limited quantitative research focuses on the deteriorations. Therefore, 30 CFRP specimens were designed and tested under elevated temperatures (10, 30, 50, 70, and 90 °C) to explore the degradations in tensile properties. The effect of temperature on the failure mode, stress-strain curve, tensile strength, elastic modulus and elongation of CFRP plates were investigated. The results showed that elevated temperature exposure significantly changed the failure characteristics. When the exposed temperature increased from 10 °C to 90 °C, the failure mode changed from the global factures in the whole CFRP plate to the successive fractures in carbon fibers. Moreover, with temperatures increasing, tensile strength and elongation of CFRP plates decreases gradually while the elastic modulus shows negligible change. Finally, the results of One-Way Analysis of Variance (ANOVA) show that the degradation of the tensile strength of CFRP plates was due to the impact of elevated temperature exposure, rather than the test error. Full article

(This article belongs to the Special Issue Carbon Fibre Reinforced Plastics)

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16 pages, 5915 KiB

Open AccessArticle

Cross-Influence between Intra-Laminar Damages and Fibre Bridging at the Skin–Stringer Interface in Stiffened Composite Panels under Compression

by Angela Russo, Andrea Sellitto, Salvatore Saputo, Valerio Acanfora and Aniello Riccio

Materials 2019, 12(11), 1856; https://doi.org/10.3390/ma12111856 - 7 Jun 2019

Cited by 13 | Viewed by 2432

Abstract

In this paper, the skin–stringer separation phenomenon that occurs in stiffened composite panels under compression is numerically studied. Since the mode I fracture toughness and, consequently, the skin–stringer separation can be influenced by the fibre bridging phenomenon at the skin–stringer interface, in this study, comparisons among three different material systems with different fibre bridging sensitivities have been carried out. Indeed, a reference material system has been compared, in terms of toughness performance, against two materials with different degrees of sensitivity to fibre bridging. A robust numerical procedure for the delamination assessment has been used to mimic the skin–stringer separation. When analysing the global compressive behaviour of the stiffened panel, intra-laminar damages have been considered in conjunction with skin–stringer debonding to evaluate the effect of the fibre and matrix breakage on the separation between the skin and the stringer for the three analysed material systems. The latter are characterised by different toughness characteristics and fibre bridging sensitivities, resulting in a different material toughness. Full article

(This article belongs to the Special Issue Carbon Fibre Reinforced Plastics)

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15 pages, 5196 KiB

Open AccessFeature PaperArticle

Mode-I Fracture Behavior of CFRPs: Numerical Model of the Experimental Results

by Claudia Barile, Caterina Casavola, Benedetto Gambino, Alessandro Mellone and Marco Spagnolo

Materials 2019, 12(3), 513; https://doi.org/10.3390/ma12030513 - 8 Feb 2019

Cited by 8 | Viewed by 5647

Abstract

In the last decades, the increasing use of laminate materials, such as carbon fibre reinforced plastics, in several engineering applications has pushed researchers to deeply investigate their mechanical behavior, especially in consideration of the delamination process, which could affect their performance. The need for improving the capability of the current instruments in predicting some collapse or strength reduction due to hidden damages leads to the necessity to combine numerical models with experimental campaigns. The validation of the numerical models could give useful information about the mechanical response of the materials, providing predictive data about their lifetime. The purpose of the delamination tests is to collect reliable results by monitoring the delamination growth of the simulated in situ cracking and use them to validate the numerical models. In this work, an experimental campaign was carried out on high performance composite laminates with respect to the delamination mode I; subsequently, a numerical model representative of the experimental setup was built. The ANSYS Workbench Suite was used to simulate the delamination phenomena and modeFRONTIER was applied for the numerical/experimental calibration of the constitutive relationship on the basis of the delamination process, whose mechanism was implemented by means of the cohesive zone material (CZM) model. Full article

(This article belongs to the Special Issue Carbon Fibre Reinforced Plastics)

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14 pages, 3249 KiB

Open AccessArticle

Experimental Study on Interfacial Bond Behavior between CFRP Sheets and Steel Plates under Fatigue Loading

by Long Zhang, Shuangyin Cao and Xin Tao

Materials 2019, 12(3), 377; https://doi.org/10.3390/ma12030377 - 25 Jan 2019

Cited by 19 | Viewed by 2780

Abstract

Using carbon fiber reinforced polymer (CFRP) composites for enhancing the fatigue behavior of the steel structures will be an important application. As the most critical part, the fatigue behavior of the CFRP-to-steel bonded interface directly determines the strengthening effect of steel structures reinforced by CFRP. In this paper, a series of CFRP-to-steel double-shear specimens are performed in order to study the interfacial bond behavior between CFRP and steel under fatigue loading. Two parameters are considered: the upper bound value and the lower bound value of the fatigue loading. An analysis of test results indicates that the crack development rate increases with the increment of the stress ratio or stress level and the crack development process includes two phases: crack stable development phase and debonding failure phase. A calculation model is put forward to describe the relationship between the crack development rate and the stress level. Besides, it can be obtained from the test results that the fatigue lives of the specimens decrease with the increment of the stress level. The empirical formula of S-N curve based on the form of single logarithm formula is proposed and the fatigue limit under the experimental conditions in this paper is determined to be 0.343 by computational analysis. Full article

(This article belongs to the Special Issue Carbon Fibre Reinforced Plastics)

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14 pages, 5233 KiB

Open AccessArticle

Digital Image Correlation Comparison of Damaged and Undamaged Aeronautical CFRPs During Compression Tests

by Claudia Barile, Caterina Casavola and Giovanni Pappalettera

Materials 2019, 12(2), 249; https://doi.org/10.3390/ma12020249 - 13 Jan 2019

Cited by 16 | Viewed by 3736

Abstract

The diffusion of composite materials in aeronautical and aerospace applications is attributable to the high specific mechanical properties they offer. In particular, the recent use of Carbon Fiber Reinforced Polymer (CFRP) materials is highly increased. The main disadvantage in using this kind of material is related to the possibility of including damages or defects not visible on the surface that compromise their behavior and make their use extremely unsafe if not properly supervised. The most conventional nondestructive techniques allow the detection of damages when they already compromise the life of these materials. The use of the same techniques makes it harder to monitor in-situ of the progress of damages, especially if they occur inside the materials. The implementation of the innovative strain analysis method, like those based on full-field measurements, could provide additional information about the damage mechanisms by supplying the complete strain distribution of the surface of the sample. The present paper examines the mechanical behavior of two different CFRP specimens, with and without damage, subjected to compressive load in an anti-buckling fixture by using the Digital Image Correlation (DIC). The purpose is to measure the out-of-plane displacements, characteristics of the compression tests, in all the points of the ROI (Region of Interest), using a full-field and noncontact technique. The innovative aspect of this work is therefore to solve this problem through an experimental approach with DIC 3D technique. Full article

(This article belongs to the Special Issue Carbon Fibre Reinforced Plastics)

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17 pages, 3648 KiB

Open AccessFeature PaperArticle

Improvement of a Cohesive Zone Model for Fatigue Delamination Rate Simulation

by Alessandro Pirondi and Fabrizio Moroni

Materials 2019, 12(1), 181; https://doi.org/10.3390/ma12010181 - 7 Jan 2019

Cited by 16 | Viewed by 4321

Abstract

The cohesive zone model (CZM) has found wide acceptance as a tool for the simulation of delamination in composites and debonding in bonded joints and various implementations of the cohesive zone model dedicated to fatigue problems have been proposed in the past decade. In previous works, the authors have developed a model based on cohesive zone to simulate the propagation of fatigue defects where damage acts on cohesive stiffness, with an initial (undamaged) stiffness representative of that of the entire thickness of an adhesive layer. In the case of a stiffness that is order of magnitude higher than the previous one (for instance, in the simulation of the ply-to-ply interface in composites), the model prediction becomes inaccurate. In this work, a new formulation of the model that overcomes this limitation is developed. Finite element simulations have been conducted on a mode I, constant bending (constant G)-loaded double cantilever beam (DCB) joint to assess the response of the new model with respect to the original one for varying initial stiffness K₀ and cohesive strength σ₀. The results showed that the modified model is robust with respect to changes of two orders of magnitude in initial stiffness and of a factor of two in σ₀. Full article

(This article belongs to the Special Issue Carbon Fibre Reinforced Plastics)

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16 pages, 4240 KiB

Open AccessFeature PaperArticle

Thermomechanical and Morphological Studies of CFRP Tested in Different Environmental Conditions

by Claudia Barile, Caterina Casavola, Paramsamy Kannan Vimalathithan, Marco Pugliese and Vincenzo Maiorano

Materials 2019, 12(1), 63; https://doi.org/10.3390/ma12010063 - 25 Dec 2018

Cited by 13 | Viewed by 2597

Abstract

The present work describes the mechanical characterization combined with the thermal degradation kinetics of Carbon Fiber Reinforced Polymers (CFRP). The thermal degradation kinetics of CFRP have never been studied in the past. In that regard, the present work focuses on studying the thermal degradation kinetics of CFRP tested mechanically at different environmental conditions. Tensile tests were performed on the specimens with different lay-ups at room temperature, elevated temperature (71 °C), and cryogenic conditions (−54 °C), and the same specimens were used for thermal degradation kinetic studies. Mechanical tests show different responses respect to the different environmental conditions and different fibers orientation. On the other hand, the thermogravimetric results, mass loss, and derivative mass loss, show no significant difference in the degradation of CFRP tested at different temperatures. However, the thermal degradation kinetics shows more insight into the degradation pattern of the materials. The activation energy of degradation shows that the degradation of materials subjected to elevated conditions increases rapidly in the later stages of degradation, suggesting the formation of high char yield. The varying activation energy has been related to different degradation mechanisms. Lastly, the morphology of the materials was studied under SEM to understand the structural change in the material after tested in different weather conditions. Full article

(This article belongs to the Special Issue Carbon Fibre Reinforced Plastics)

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Review

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17 pages, 13051 KiB

Open AccessFeature PaperReview

Mechanical and Impact Damage Analysis on Carbon/Natural Fibers Hybrid Composites: A Review

by Carlo Santulli

Materials 2019, 12(3), 517; https://doi.org/10.3390/ma12030517 - 9 Feb 2019

Cited by 54 | Viewed by 5674

Abstract

Hybrid composite laminates including carbon fibers and natural fibers, hence basalt and/or vegetable ones, draw on the experiences accumulated in studying the hybridization of fiberglass with carbon or natural fibers. Yet, in the case of carbon/natural fiber composites, the sense is different: in particular, the idea is to accept the reduction of properties from bare carbon fiber composites and the unavoidable complication in processing, induced by hybridization. The compensation obtained, which offers a rationale to this operation, is the improved toughness and a significant modification of the different modes of failure. This would bring a higher energy absorption and a substantially more effective damage tolerance. The aforementioned characteristics are particularly of interest in the case of flexural properties, impact properties, and residual post-impact performance. Full article

(This article belongs to the Special Issue Carbon Fibre Reinforced Plastics)

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