Predicting very high cycle fatigue (VHCF) life in composites is challenging due to the lengthy testing times required by traditional methods. Ensuring compatibility between VHCF and high cycle fatigue (HCF) data presents an additional challenge. This investigation examines CF-PEKK fatigue behavior under low and ultrasonic cyclic frequencies using a thermographic approach and the Fracture Fatigue Entropy (FFE) concept. Constant-amplitude fatigue (CAF) and increasing-amplitude fatigue (IAF) tests were conducted, with self-heating behavior analyzed for different loading conditions. Digital Image Correlation (DIC) and finite element analysis (FEA) enabled stress estimation for each test setup. Heat dissipation rates from IAF experiments and fatigue data from three CAF experiments at 40 Hz and three at 20 kHz were used to calculate FFE values. Results showed that the self-heating response of CF-PEKK specimens helps achieve comparable fatigue data across frequencies, with consistent FFE ranges identified between HCF and VHCF regimes. This consistency highlights that FFE can provide reliable fatigue life estimation for composites. Thermographic and microscopic analyses further confirmed this approach as an efficient method for estimating fatigue life under various cyclic loading conditions.

In this study, cyclic loading is applied to the specimen placed in an autoclave with varied hydrogen gas pressure. The effect of hydrogen pressure and stress fluctuations on the fatigue crack growth rate is analyzed. The results show that the crack growth rate increases with the increase of hydrogen pressure, and under 3 MPa hydrogen pressure, the crack growth rate can be enhanced by one order compared with that in air. With the increase of loading frequency, the crack propagation rate of a single block decreases in hydrogen, while the crack growth rate remains constant in air. As the maximum stress is fixed during cyclic loading, the fatigue crack growth rate increases with the stress range. Based on the experimental results, a predictive model is proposed to quantify the crack growth rate under different hydrogen pressure and loading conditions.

The processing of barbs in sutures introduces cracks, reducing the fracture resistance of the barbed sutures. Obtaining stress intensity factor (SIF) is pivotal for the optimal design and safe usage of barbed sutures. In this study, an explicit method was proposed to calculate the SIFs for barbed suture with Mode Ⅰ crack under arbitrary stress distribution. The barbed suture was modeled as a round bar with different shapes of mode Ⅰ cracks. The shape coefficient, which was defined to describe the shape of crack, was computed using the point load weight function. Based on these shape coefficients, the basic stress intensity factors (BSIFs) for cracks under basic stress distributions, such as uniform, linear, and quadratic stress distributions, were determined. Then, the SIFs under arbitrary stress distributions were calculated through linear superposition of these BSIFs according to the corresponding stress distribution. The relative errors between the SIFs calculated by this method and the finite element are commonly within ±8%. This demonstrates that the proposed explicit method is capable of directly and accurately calculating SIFs for round bars with mode Ⅰ cracks under arbitrary stress distributions, thereby avoiding the time-consuming processes of finite element analysis and numerical integration.

This study proposes a novel method for predicting material creep behavior based on the ZC parameter method using limited creep strain data, aiming to address the limitations of traditional creep prediction methods under conditions of high data variability and incomplete experimental data. A systematic prediction of the creep behavior of DZ125 alloy was conducted, analyzing the creep curves and rupture lifespans under varying temperature and stress conditions. The results indicate that the ZC parameter method can accurately predict complete creep curves from limited creep stress-time data, with predicted values closely aligning with experimental data; all predicted data points fall within the 95% confidence interval. Furthermore, the ZC parameter method covers a broader strain range with smaller errors in lifespan predictions, offering a reliable approach for forecasting the creep behavior of high-temperature alloy materials. The study provides new theoretical support and practical application references for the prediction of creep performance in materials.

not-yet-known not-yet-known not-yet-known unknown Steel cooling towers, with their lighter weight, greater flexibility, and lower damping, are more susceptible to wind-induced damage compared to hyperbolic concrete towers. This study investigates the fatigue fracture mechanisms of cylindrical–conical steel cooling towers (CCSCT) under high wind loads. Large eddy simulation (LES) techniques determine the three-dimensional wind load distribution, and a 3D finite element model incorporating elastoplastic material damage is developed in LS-DYNA to simulate the wind-induced collapse process. Results reveal a critical wind speed of 52 m/s, with failure mechanisms driven by interlayer translation and cross-sectional deformation. The stiffening trusses restrict section deformation but concentrate internal forces, while the auxiliary trusses mitigate these forces and provide stability. Key fracture zones include the conical section top (72°, -108°) and tower top (0°) for tension, and tower top (±12°) for compression. These findings provide insights into fatigue mechanisms for enhancing wind-resistant design.

In recent decades, natural fibers reinforced composites in various applications have significantly developed. One of the critical properties of hybrid composites is their fatigue behavior, which affects the lifetime and application range of these materials, especially when the composite is drilled. This study aims to analyze the fatigue behavior of the central open-hole kenaf/glass multilayer hybrid composites. For this purpose, pure and hybrid kenaf/glass four layers composite samples with different stacking sequences, with and without a central hole were produced, and their tensile strength was evaluated. Afterward, the optimized hybrid composite (GKKG) and two pure glass (G4) and kenaf (K4) samples were analyzed under the fatigue tensile test at three stress levels. The results showed that the four layers drilled pure glass sample exhibited the highest fatigue strength, enduring 115,000 cycles at a stress level of 50%. The drilled hybrid kenaf/glass sample (GKKG) also showed outstanding fatigue strength, bearing approximately 54,000 cycles at a stress level of 50%. The slope of the stress-logarithm(N) curve of the hybrid sample was considerably smaller than the pure glass. This indicates lower sensitivity of drilled hybrid composites reinforced with natural fibers to the fatigue loading.

Fish-eye morphology is commonly observed in the very high cycle fatigue (VHCF) regime of additively manufactured Ti-6Al-4V alloys. However, its occurrence and implications have been less extensively studied in the high cycle fatigue (HCF) regime. In this paper, the fatigue performance and relationship between fish-eye morphology, fatigue life, and stress amplitude of selective laser melting (SLM) Ti-6Al-4V alloys were investigated in the HCF regime. Additionally, an in-depth analysis revealed that crack initiation in hot isostatic pressing (HIP) treated Ti-6Al-4V alloys predominantly occurs at facets, with a relationship identified between crack initiation sites and localized oxidation. Finally, based on the stress intensity factor (∆𝐾), a mechanistic model is proposed to explain the crack initiation and propagation behavior associated with fish-eye morphology in the HCF regime.

In-situ fatigue crack propagation experiment was conducted on laser cladding with coaxial powder feeding (LCPF) K477 under various stress ratios and temperatures. Multiple crack initiation sites were observed by using in-situ scanning electron microscopy (SEM). The fatigue short crack growth rate was measured, and the impacts of temperature and stress ratio on this growth rate were analyzed. Based on these experiments, the experimental data were expanded, and three ensemble learning algorithms, i.e. random forest (RF), extreme gradient boosting (XGBoost) and light gradient boosting machine (LightGBM) were employed to establish a fatigue short crack growth rate model controlled by multiple parameters. It is indicated that the RF model performs the best, achieving a coefficient of determination ( R 2) of up to 0.88. The fatigue life predicted by the machine learning (ML) method agrees well with the experimental one.

In this paper, the damage mechanisms and residual strength prediction models of unidirectional glass-fiber reinforced polymers are investigated by acoustic emission(AE) technique. The material exhibits three damage modes: matrix cracking, fiber fracture, and interface damage. A novel AE descriptor, amplitude/centroid frequency (ACF), is introduced to differentiate interface damage from other damage modes. Moreover, three signal types exhibit a strong clustering effect when correlated with ACF and average frequency. Microscopic damage mechanisms of the samples are observed using scanning electron microscopy and correlated with AE signals. The AE signals are analyzed using machine learning, and the clustering analysis results are used as a training set to obtain classification models using support vector machine (SVM) and K-nearest neighbor (KNN) methods. Leveraging the traditional mechanical regression analysis prediction model, the study achieves prediction of the material’s residual strength post-fatigue through improvement in AE cumulative counting. Additionally, optimization of prediction results can be achieved by a certain kind of signal after clustering. The combination of supervised learning and residual strength prediction models can realize the real-time classification of AE signals and apply them to the prediction of residual strength, which has a significant application value in real-time monitoring.

Crack initiation in AISI 316 stainless steel has been investigated. Persistent Slip bands (PSBs) were characterized using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). PSBs on the surface of the material increase the surface roughness and result in crack initiation. EBSD data from near the crack initiation region were used to correlate the global and local misorientations of the grains, plastic deformation, and Schmid Factor with the fatigue life of specimens. The crack initiation region was found to have the highest misorientations. The region near crack initiation was found to have more plastic deformation, which was severe in specimens loaded with higher stresses. The Kernel Average Misorientation (KAM) and Grain Reference Orientation Deviation (GROD) maps from the EBSD data were investigated for specimens that failed at different fatigue cycles. It was found that the interaction of high dislocation density, substructuring and misorientation of low-angle grain boundaries in the region of plastic deformation resulted in the fatigue crack initiation.

not-yet-known not-yet-known not-yet-known unknown Fatigue characterization of asphalt mixtures is imperative for predicting pavement performance. Since cracking begins in asphalt binders, determining their fatigue properties helps establish cause-and-effect relationships with cracking in mixtures and pavements. This study analyzes the fatigue of 12 Brazilian asphalt binders and mixtures using the Linear Amplitude Sweep (LAS) test for binders and the Direct Tension Cyclic Fatigue test for mixtures. Results were interpreted with Simplified Viscoelastic Continuous Damage theory (S-VECD) and a pavement was simulated using FlexPAVE TM software. Findings indicate that binder type alone does not predict fatigue class through the fatigue factor of binder (FFB), necessitating rheological damage analysis. Most mixtures showed good performance in pavement simulations, with fatigue factor of mixtures (FFM) and fatigue classes not being sufficient for predicting fatigue performance. A linear correlation was found between FFB and FFM but not between FFB and simulated damage (N/Nf), though higher FFB typically result in lower N/Nf.

This study aims to investigate the low cycle fatigue (LCF) behavior and fatigue life prediction method of an advanced solid solution strengthened nickel-based superalloy at various temperatures and stress concentrations. Cylindrical specimens as well as plates with three types of holes (including straight holes and inclined holes with different orientations) were designed and machined for fatigue tests. The test results revealed fatigue life decreases with the temperature increasing. Meanwhile, the fatigue lives of the plate specimens have decreased differently and are strongly dependent on the geometry and orientation of the holes. The key damage parameter related to the fatigue life was found on the strain gradient path. A criterion based on strain gradient is defined as the boundary of the damage process zone. The results show that the prediction was in good agreement with the experimental data, for the majority of the data is within a scatter band of ±2.

Three fatigue damage models based on entropy, originally developed for constant amplitude loading, were assessed and compared each other in order to state whether its applicability can be extended towards variable amplitude loading conditions. A variable amplitude loading history, applied on a 2024-T3 aluminum alloy reported in the literature, was processed using both rainflow cycle counting and spectral techniques to transform it into a distribution of simple processes with constant amplitudes, then the damage models were assessed under the new loading conditions. The results showed that the model by Khonsari, combined with the rainflow technique, exhibited the highest accuracy with respect to the referenced experimental results with -0.67 standard deviation from the average data and 16% error from the median. Therefore, it is possible to assess the fatigue damage accumulation in metallic materials under variable amplitude loading through a thermodynamic approach with models developed for constant amplitude loading.

A unified phase-field theory is introduced to describe crack initiation and early crack growth due to pitting corrosion of pipelines in contact with near-neutral pH groundwater. The model incorporates a formulation that accounts for stochastic corrosion-induced crack nucleation events at pit sites. This approach supplies a modeling framework to handle the combined effects of electrochemical transformation of the original metal, hydrogen diffusion and resulting embrittlement of the original metal, and mechanical stresses. This is a robust computational approach to tracking the evolving metalelectrolyte interface and embrittlement regions. It was confirmed that dissolved hydrogen into the material promotes crack initiation over a wide potential range and that pitting corrosion, as a precursor of stress corrosion cracking, has a recognizable influence on strength over time. It is expected that this work provides the ground for modeling the pit-to-crack transition required to effectively control very slow crack-in-colonies in pipelines.

In this article, the low cycle fatigue(LCF) behavior of a low silicon cast aluminum alloy Al-3.5Si-0.5Mg-0.4Cu with T6 treat-state at room temperature is investigated by extracting samples from aluminum steering knuckles. Initial microstructure, cyclic stress response behavior and fatigue fracture are studied. Low cycle fatigue experiment results and behavior performance of 6 different total strain amplitudes are included. OM, SEM, XRD and TEM are carried out to observe pre(post)-fatigue microstructures and fracture. The results demonstrate that cracks initiate from surface or subsurface defects and higher total strain amplitude leads to larger sum area of fatigue crack initiation region and steady crack propagation region, and wider fatigue striation bandwidth. Furthermore, crack propagates along the interface between eutectic silicon and α-Al under low strain amplitude while crack grows through eutectic silicon particle if higher strain amplitude is applied.

Variable creep load is one of the most important failure modes for hot-component of aero-engine. To accurately predict creep damage and remaining life, a novel nonlinear creep damage accumulation model is proposed based on the Wilshire function and isodamage line, which takes the influence of load history into account and uses ultimate tension strength to compensate the temperature effect. Experimental result of tests on four kinds of material were utilized to verify the accuracy of the proposed model and to compare it with existing models. It was determined that the novel model was better at predicting damage accumulation than all others model. Furthermore, the proposed model elucidates the evolutionary process of creep damage, and four cases of damage evolution process are discussed.

A comparison study of fatigue behavior in Al-Al and Al-steel refill friction stir spot welding jointHaokun Yang1a*, Detao Cai2,3a, Jiaxin Li1, Chin Yung Kwok1, Yunqiang Zhao3, Yu Li4, Haisheng Liu4, Waiwah Lai11 Smart Manufacturing Division (SMD), Hong Kong Productivity Council (HKPC), Hong Kong 999077, People’s Republic of China2 State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body, Hunan University, Changsha, Hunan 410082, People’s Republic of China3 China-Ukraine Belt and Road Joint Laboratory on Materials Joining and Advanced Manufacturing, China-Ukraine Institute of Welding Guangdong Academy of Sciences, Guangzhou, Guangdong 510650, People’s Republic of China4 Center for Industrial Analysis and Testing, Guangdong Academy of Science, Guangzhou, Guangdong 510650, People’s Republic of Chinaa These authors contribute equallyCorresponding author: Haokun Yang, +852 27885679,hkyang@hkpc.orgKeywords: Refill friction stir spot welding, Fatigue fracture, Aluminum, Steel

In this paper, a theoretical analysis model and two simulation methods are applied to characterize the quasi-static and fatigue delamination of composite laminate with uneven thicknesses. The test data of partially reinforced double-cantilever beam (DCB) were used as benchmark to verify the analysis model and simulation, and cohesive zone models (CZMs) and virtual crack closure technique (VCCT) are used in simulation. It’s shown that the partially reinforced DCB has a unique double-peak load-displacement relationship, and produces instability development during the delamination. By comparing the results of simulation and experiment, it is found that the simulation based on the exponential CZM can simulate the delamination process of partially reinforced DCB under both quasi-static and fatigue loading; while VCCT method will generate a straight delamination front edge in the area of reinforcement, and lost the micro-damage of the previous loading step between load steps, and result in an incorrect delamination behavior.