Search Results (152)

A nonlinear ultrasonic time-domain identification method based on chaos sensitivity was proposed in this study. The Duffing chaotic system was introduced into the weak second harmonic identification to realize early detection and quantitative evaluation of fatigue damage in U71Mn steel. First, to ensure the reliability of nonlinear ultrasonic testing, a probe-pressure monitoring device was designed. Through pressure-stability experiments, 16 N was determined as the optimal pressure, which effectively suppresses contact nonlinearity interference and ensures coupling stability. Subsequently, the Duffing chaos detection system was established. The signal-system frequency-matching problem was resolved through time-scale transformation. Simultaneously, the issue of unknown initial phases was resolved using phase traversal compensation. Based on the chaotic system’s sensitivity to specific frequency signals and immunity to noise, the amplitudes of the fundamental wave and second harmonics in the target signals were quantified to calculate the nonlinear coefficient. Experimental results demonstrate that the proposed method can extract these amplitudes directly in the time domain, thereby effectively overcoming the spectral leakage inherent in traditional frequency-domain methods. The nonlinear coefficient of U71Mn steel exhibits a “double-peak” characteristic as fatigue damage increases. Specifically, the first peak appears at approximately 50% of fatigue life, while the second occurs at approximately 80%. This phenomenon is closely correlated with the distinct stages of internal fatigue crack propagation, reflecting a complex damage-evolution mechanism. This study not only provides a novel method for the precise extraction of weak nonlinear signals but also establishes a critical theoretical and experimental foundation for accurate fatigue life prediction for U71Mn rail steel. Full article

This study investigates the development of advanced protective gloves by applying novel 3D-printed PET-G mesh overlay structures onto three textile substrates—polyamide (PA), polyester (PES), and cotton—using ultrasonic welding and contact welding. The focus was on assessing weld quality, thickness uniformity, and functional durability. Weld morphology and bonding integrity were evaluated using X-ray microtomography (micro-CT), while bending fatigue tests assessed mechanical performance under cyclic loading. The results show that ultrasonic welding produces more uniform welds, enhancing fatigue resistance, particularly on cotton and polyamide substrates. Non-uniform welds with thicker or uneven areas, typical of contact welding, correlated with reduced mechanical durability. These findings highlight the potential of additively manufactured overlay structures for hybrid protective gloves, demonstrating that weld thickness uniformity and substrate compatibility are key factors in optimizing mechanical performance. This work extends our previous research by introducing new 3D-printed overlay architectures and provides valuable insights into the practical implementation of additively manufactured polymeric structures in PPE development. Full article

This review presents a comprehensive examination of the total fatigue life behaviour of high-strength steels (HSS) with particular emphasis on fatigue crack initiation in the very high cycle fatigue (VHCF) regime and crack propagation based on fracture mechanics. The discussion draws on recent advances in experimental techniques, microstructural characterisation, and analytical approaches by reviewing studies conducted over the past few years. Key factors influencing fatigue performance, including loading frequency, specimen geometry, microstructure, and environmental conditions, are critically evaluated. The review concludes by highlighting existing knowledge gaps and outlining directions for future research aimed at improving the understanding and optimisation of fatigue performance in current and next-generation HSS. Full article

To address the prediction of fatigue damage for 3D-printed Carbon Fiber Reinforced Polymer (CFRP), this study used 3D-printing technology to fabricate CFRP specimens. Through multi-stage fatigue testing, samples with varying porosity levels were obtained. Based on porosity test results and ultrasonic attenuation coefficient measurements of specimens under different fatigue cycle counts, a quantitative relationship model was established between the porosity and ultrasonic attenuation coefficient of 3D-printed CFRP. According to the porosity and fatigue-loading cycles obtained from tests, the Time-series Generative Adversarial Network (TimeGAN) algorithm was employed for data augmentation to meet the requirements for neural-network training. Subsequently, the Long Short-Term Memory (LSTM) neural network was utilized to predict the fatigue damage evolution of 3D-printed CFRP specimens. Research findings indicate that by integrating the established relationship between porosity and ultrasonic attenuation coefficient, non-destructive testing of material fatigue damage evolution based on ultrasonic attenuation coefficient can be achieved. Full article

Rapid characterization of high-cycle fatigue behaviour is of great interest, since conventional methods for developing S-N curves for longer fatigue lives are both costly in time and financial resources. Ultrasonic fatigue testing offers a promising alternative by enabling S-N curve evaluation in a fraction of the time, often hundreds of times faster, due to its high testing frequencies. Nevertheless, this technique presents specific challenges, including material overheating and limitations in specimens’ geometry. Most ultrasonic fatigue studies employ hourglass specimens; however, this geometry restricts the testing of sheets and thin-walled components, which are increasingly used for their reduced mass and high stiffness-to-mass ratio. To overcome this limitation, the present work introduces a methodology for designing and testing flat specimens and corresponding gripping systems tailored to such components. The procedure is demonstrated for an aluminium alloy (6082), and preliminary experimental fatigue results are presented and compared with literature. Full article

The increased test frequency inherent in Ultrasonic Fatigue Testing (UFT) is commonly observed to result in an increased fatigue resistance for ferritic, low-carbon steels. In this investigation, the fatigue response of S275J2 ferritic structural steel is evaluated at both 20 kHz and 50 Hz. At the ultrasonic frequency, an increase in the fatigue limit of 136 MPa and an increase in the finite life region of 150 MPa was observed, alongside a reduction in the slope of the S-N curve. By combining the S275J2 results with additional data from the literature, generalised versions of previously proposed frequency sensitivity models are produced by evaluating the model coefficients as a function of different combinations of the material properties. Additionally, a new frequency sensitivity model was proposed by evaluating the empirical change in the S-N curve coefficients as a function of these material properties. For all of the models, it was found that the best correlation was against the ferrite content divided by the tensile strength. The generalised forms of these models were rearranged to produce correction factors, which allow the conventional frequency fatigue response to be estimated based on the UFT test. The most reliable correction method was found to be using the empirical change in the S-N curve exponent. Full article

The gear transmission system is a safety-critical component in rail transit, typically designed for a service life exceeding 20 years. Failure analysis of such systems remains a key focus for railway engineers. This study systematically investigates four representative cases of premature gear failure in high-speed trains using a standardized analytical procedure that includes visual inspection, chemical analysis, metallographic examination, scanning electron microscopy, and hardness testing. The results identify four primary root causes: subsurface slag inclusions in raw materials, inadequate heat treatment leading to a non-martensitic layer (∼60 μm) at the tooth root, grinding-induced temper burns (crescent-shaped "black spots") accompanied by a hardness drop of ∼100–150 HV, and insufficient lubrication. The interdependencies between these factors and failure mechanisms, e.g., fatigue cracking, spalling, and thermal scuffing, are analyzed. This work provides an evidence-based framework for improving gear reliability and proposes targeted countermeasures, such as ultrasonic inclusion screening and real-time grinding temperature control, to extend operational lifespans. Full article

As the world increasingly gravitates towards green, environmentally friendly and low-carbon lifestyles, wind power has become one of the most technologically established renewable energy sources. However, with the continuous increase in their output power and height, wind turbine towers are subjected to higher-intensity alternating wind loads. This makes critical components more prone to fatigue failure, potentially leading to major accidents such as tower buckling or turbine collapse. High-strength bolts play a vital role in supporting towers but are susceptible to fatigue crack initiation under long-term cyclic loading, necessitating regular inspection. Types of wind turbine bolts mainly include high-strength bolts, stainless steel bolts, anchor bolts, titanium alloy bolts, and adjustable bolts. These bolts are distributed across different parts of the turbine and perform distinct functions. Among them, high-strength bolts in the tower are particularly critical for structural support, demanding prioritized periodic inspection. Compared to destructive offline inspection methods requiring bolt disassembly, non-destructive testing (NDT) has emerged as a trend in defect detection technologies. Therefore, this review comprehensively examines various types of NDT techniques for wind turbine towers’ high-strength bolts, including disassembly inspection techniques (magnetic particle inspection, penetration inspection, intelligent torque inspection, etc.) and non-disassembly inspection techniques (ultrasonic inspection, radiographic inspection, infrared thermographic inspection, etc.). For each technique, we analyze the fundamental principles, technical characteristics, and limitations, while emphasizing the interconnections between the methodologies. Finally, we discuss potential future research directions for bolt defect NDT technologies. Full article

In the saline soil area of western China, the concrete is simultaneously subjected to cyclic loading and sulfate attack. To reveal the effect of sulfate attack on fatigue performance of normal concrete (NC) and hybrid fiber-reinforced rubber concrete (HFRRC), the uniaxial compression test and cyclic loading test were carried out on the specimens after sulfate erosion. The loading strain, plastic strain, and elastic strain of the concrete were compared and analyzed. The compressive strength, fatigue resistance, and strain energy of the concrete were compared and analyzed. Ultrasonic Pulse Velocity (UPV) measurements were also used to quantify the damage in sulfate attack tests. The results indicate that the fatigue failure stress of concrete is lower than its uniaxial compressive strength. The fatigue resistance coefficient of HFRRC is always higher than that of NC. Under the cyclic loading with the same level, the stress–strain curve of HFRRC is denser than that of NC, exhibiting good elasticity. The energy evolution is independent of whether or not sulfate attacks, but its growth rate is affected by sulfate erosion time. It can provide an experimental and theoretical foundation for the application of HFRRC in engineering structures subjected to repeated loads in sulfate environments. Full article

Cavitation-induced degradation of metallic materials presents a significant challenge for engineers and users of equipment operating with high-velocity fluids. For any metallic material, the mechanical strength and ductility characteristics are controlled by the mobility of dislocations and their interaction with other defects in the crystal lattice (such as dissolved foreign atoms, grain boundaries, phase separation surfaces, etc.). The increase in mechanical properties, and consequently the resistance to cavitation erosion, is possible through the application of heat treatments and cold plastic deformation processes. These factors induce a series of hardening mechanisms that create structural barriers limiting the mobility of dislocations. Cavitation tests involve exposing a specimen to repeated short-duration erosion cycles, followed by mass loss measurements and surface morphology examinations using optical microscopy and scanning electron microscopy (SEM). The results obtained allow for a detailed study of the actual wear processes affecting the tested material and provide a solid foundation for understanding the degradation mechanism. The tested material is the Ni-based alloy INCONEL 625, subjected to stress-relief annealing heat treatment. Experiments were conducted using an ultrasonic vibratory device operating at a frequency of 20 kHz and an amplitude of 50 µm. Microstructural analyses showed that slip bands formed due to shock wave impacts serve as preferential sites for fatigue failure of the material. Material removal occurs along these slip bands, and microjets result in pits with sizes of several micrometers. Full article

In recent decades, the application of composite materials in aerostructures has significantly increased, with modern commercial aircraft progressively replacing aluminum alloys with composite components. This shift is exemplified by comparing the material compositions of the Boeing 777 and the Boeing 787 (Dreamliner). The Boeing 777 incorporates approximately 50% aluminum alloy and 12% composite materials, whereas the Dreamliner reverses this ratio, utilizing around 50% composites and 12% aluminum alloy. While metals remain advantageous due to their availability and ease of machining, composites offer greater potential for property tailoring to meet specific performance requirements. They also provide superior strength-to-weight ratios and enhanced resistance to corrosion and fatigue. To ensure the reliability of composites in aerospace applications, comprehensive testing under various loading conditions, particularly impact, is essential. Impacts were performed on quasi-isotropic (QIT) carbon-fiber reinforced epoxy panels with stainless steel, round-nosed and flat-ended impactors with rubber discs of 1-, 1.5- and 2 mm thickness, adhered to the flat-ended impactor to simulate the transition between hard and soft impact loading conditions. QIT composite panels were tested in this research employing similar lay-ups often being implemented in aircraft wings and other structures. The rubber discs were applied in the flat-ended impactor case but not for the round-nosed impactor due to the limited adhesion between the rubber and the rounded stainless-steel surface. Impact energies of 7.5, 15 and 30 J were investigated, and the performance of the panels was evaluated using force-time and force-displacement data alongside post-impact ultrasonic C-scan imaging to assess the damaged area. Damage was observed at all three energy values for the round-nosed impacts but only at the highest impact energy when using the flat-ended impactor, leading to the hardness study with adhered rubber discs being performed at 30 J. The most noticeable difference with the addition of rubber discs was the reduction in the damage in the plies nearest the top (impacted) surface. This suggests that the rubber reduces the severity of the impact, but increasing the thickness of the rubber from 1 to 2 mm does not notably increase this effect. Indentation clearly plays a significant role in promoting delamination at low-impact energies for the round-nosed impactors. Full article

Performing fatigue characterisation is often an expensive task, being both time consuming and expensive. Taking that into account, ultrasonic fatigue testing is an interesting solution, since it can be thousands of times faster than traditional experiments. In ultrasonic fatigue testing, excitation frequencies are in the order of magnitude of 20 kHz, while common fatigue testing frequencies are typically approximately a few hundreds of Hz. Although promising, ultrasonic fatigue testing has some challenges, like high strain rates, heat generation and complex specimen design. Regarding the latter, since the working principle of ultrasonic fatigue tests relies on exciting the specimen in one of its natural frequencies, finding a specimen geometry to resonate at this given frequency might be challenging. Additionally, some materials often present challenges associated with high temperature during tests. The goal of this paper is to provide guidelines for specimen design, encompassing the effects of critical factors and their impact on important test parameters, like temperature and dimensions. The proposed methodology developed a parameter able to quantify the heat generation severity during ultrasonic fatigue testing for several materials based on their physical properties. Moreover, the effects of the geometry and material properties in the temperature during loading cycles, with special focus on thermal gradients were enumerated. Full article

High-speed electrical discharge machining (EDM) is crucial for drilling aerospace components, but the fatigue effects of its recast layer are still not well understood. This study investigates the fatigue behavior of high-speed EDM-processed specimens using ultrasonic fatigue testing and microscopic analysis. The recast layer showed a 20.4% increase in hardness and a 16.5% decrease in elastic modulus compared to the base material. Fatigue cracks originated from microcracks, pores, and inclusions within the recast layer, as well as at its interface with the substrate. Microscopic crack initiation was influenced by defect interactions, while macroscopic crack initiation occurred near the maximum hole diameter perpendicular to the loading direction due to stress concentration. The specimens exhibited bimodal fatigue life: shorter lifetimes were observed when macroscopic stress concentrations overlapped with recast layer defects such as cracks and voids, while defect-free regions significantly extended durability. The non-uniform distribution of the recast layer critically links microstructural heterogeneity to variations in fatigue failure. These findings highlight how recast layer characteristics influence crack nucleation and life variability in EDM-processed components, offering valuable insights for optimizing machining parameters to reduce fatigue risks in critical aerospace applications. Full article

Integrating machine learning into additive manufacturing offers transformative opportunities to optimize material properties and design high-performance, fatigue-resistant structures for critical applications in aerospace, biomedical, and structural engineering. This study explores mechanistic machine learning techniques to tailor microstructural features, leveraging data from ultrasonic fatigue tests where very high cycle fatigue properties were assessed up to $1\times {10}^{10}$ cycles. Machine learning models predicted critical fatigue thresholds, optimized process parameters, and reduced design iteration cycles by over 50%, leading to faster production of safer, more durable components. By refining grain orientation and phase uniformity, fatigue crack propagation resistance improved by 20–30%, significantly enhancing fatigue life and reliability for mission-critical aerospace components, such as turbine blades and structural airframe parts, in an industry where failure is not an option. Additionally, the machine learning-driven design of metamaterials enabled structures with a 15% weight reduction and improved yield strength, demonstrating the feasibility of bioinspired geometries for lightweight applications in space exploration, medical implants, and high-performance automotive components. In the area of titanium and aluminum alloys, machine learning identified key process parameters such as temperature gradients and cooling rates, which govern microstructural evolution and enable fatigue-resistant designs tailored for high-stress environments in aircraft, biomedical prosthetics, and high-speed transportation. Combining theoretical insights and experimental validations, this research highlights the potential of machine learning to refine microstructural properties and establish intelligent, adaptive manufacturing systems, ensuring enhanced reliability, performance, and efficiency in cutting-edge engineering applications. Full article

The valve stem made of 20CrMo1V1A has low surface resistance and high susceptibility to corrosion, significantly curtailing its service life. To address these issues, a high-quality ultrasonic rolling (USR) technology was applied to the 20CrMo1V1A stainless steel valve stem to enhance its corrosion resistance and mechanical properties. Subsequently, fatigue and corrosion tests were conducted on the valve stem. The results indicate that USR produces surfaces with a roughness average (Ra) of 0.3 μm and a gradient nanostructure on the valve stem surface. This unique microstructural modification resulted in a 27% improvement in surface hardness and nearly a three-fold grain size reduction. Additionally, the friction coefficient and electrochemical corrosion rate dropped by 47% and 32%, respectively. Therefore, USR was applicable for enhancing multiple properties of valve components as an additional final processing step for achieving high-performance valve stems. Full article