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.

This research investigates the diverse thermal reactions of additively manufactured Inconel 718 samples under cyclic dynamic loading, predominantly influenced by the Self-Heating effect. The study assesses the feasibility of utilizing thermographic techniques to construct an S-N curve for predicting fatigue life with a reduced number of samples compared to conventional constant-amplitude tests. Dedicated Self-Heating tests are performed, systematically elevating the loading amplitude while concurrently tracking the specimen's temperature. The credibility of the proposed solution is juxtaposed with our experimental data, encompassing the influence of four distinct heat treatments on samples from a single additive manufacturing build. This comparison yields valuable insights and leads to noteworthy conclusions.

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.

The enhanced fatigue resistance of superelastic Cu-Al-Mn shape memory wires were investigated via bamboo-like grain structure obtained by cyclic heat treatment (CHT). It was demonstrated that increasing the number of CHT cycles can promote the grain growth to a straight grain boundary, eliminating the triangular structure that generally caused brittle fracture. In particular, the 5CHT and 7CHT specimens displayed negligible residual strain subsequent to unloading, following exposure to cumulative strains ranging from 2% to 10%, thereby showcasing superior superelasticity. From the functional fatigue test, the fatigue life of the shape memory wire subjected to 5 CHT cycles exceeds 4650 cycles at 5 % strain, which is more than 5 times that of traditional polycrystalline quenched samples.

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.

In contrast, but complementary to previous studies, this study examines the fatigue behaviour in Ti-6Al-4V obtained by electron beam powder bed fusion, focusing on damage initiation sites, fatigue damage progression, and correlating these with fatigue life curves. Three material conditions were considered: as-built specimens with original surfaces after printing (AB), as-built specimens with a machined and polished surface (MP), and hot isostatic pressed specimens with a machined and polished surface (H). Fatigue fracture surface topography was analysed using scanning electron microscopy and surface metrology microscopy. Different fatigue responses were observed, with crack initiation at surface roughness in AB, lack of fusion defects in MP, and phase facet formation in H specimens. Interaction between cracks and manufacturing defects was investigated. Kitagawa-Takahashi diagrams were applied successfully to AB and MP specimens. This study aims to enhance understanding of crack initiation and interaction mechanisms, improving life prediction capabilities through microstructure and defect-sensitive modelling.

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,[email protected]: 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.

This work discusses the results from tests conducted to investigate the uniaxial compression and creep behavior of red sandstone. The original untreated sample and the 800 ℃ treated sample have been selected to carry out the experiments. It has been found that high temperature has obvious influence on the mechanical properties of red sandstone. The relationship between creep strain and instantaneous strain, as well as instantaneous deformation modulus and creep viscosity coefficient have been analyzed. It has been found that high temperature reduces the ability of red sandstone to resist instantaneous deformation and creep deformation. Acoustic emission (AE) technology has been also used in the loading process of uniaxial compression and creep tests, providing a powerful means for damage evolution analysis of red sandstone.

This work deals with the analysis in the frequency domain of the temperature signal and mechanical energy rate of C45 steel under two different fatigue stepwise loading series at stress ratios of 0.1 and -1. It was first investigated the energy distribution among the harmonic components of the signals to understand possible variations caused by a different stress ratio. In addition, the second amplitude harmonic (SAH) of heat dissipated and mechanical energy rates have been considered in the analysis and their relationship was investigated. It has been shown as it depends only on the material, hence it is valid whatever the kind of the test is without any assumption on the energy supplied to the material or material hysteresis loop stabilisation. The adopted approach allows the analysis of intrinsic dissipations by means of rapid, full-field and contactless techniques without any specific requirement on loading condition or temperature signal stabilisation.