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A novel fatigue model under Cosserat peridynamic framework is proposed to investigate concrete fatigue performance. In this model, a novel cyclic bond failure criterion is established to measure the combined tension/compressive-shear fatigue failure in concrete, which is derived from the Bresler-Pister criterion. Three benchmarks with different fatigue crack modes in concrete are designed. Results show that the mode I and mixed mode I-II fatigue crack patterns are predicted. In the three-point-bend beam fatigue test, the numerical result matches well with the experimental result, in the uniaxial compressive fatigue test, the effects of Cosserat parameters on fatigue crack patterns are discussed. Results found that the Cosserat parameters reflect the effects of concrete microstructures on crack patterns, and the larger Cosserat shear modulus accelerates the fatigue crack propagation process.

Self-piercing riveted (SPR) joints in automobiles inevitably suffer from corrosion damage and performance reduction. In this work, the influence of salt spray corrosion on the mechanical properties of TA1-Al5052 alloy SPR joints was studied. The TA1-5052 SPR joints were prepared and salt spray tests were carried out for different durations. The static and fatigue strengths of the joints after salt spray corrosion were tested to analyze the effect of salt spray duration on the performance of the joints. The results show that the joints’ static strength and fatigue strength decrease with prolonged salt spray time. The salt spray duration affects the joint’s tensile failure mode. The tensile failure without corrosion and with a short salt spray time is the fracture failure of the lower aluminum sheet, and the tensile failure of the joints after a long time of salt spray corrosion is the failure of the rivets. The fatigue failure form of the SPR joint is the formation of fatigue cracks in the lower aluminum sheet, and salt spray time has little effect on the fatigue failure form. Salt spray corrosion can promote the initiation and propagation of fatigue cracks. The fatigue crack initiation area is located at the boundary between the lower aluminum sheet and the rivet leg. The initiation of cracks originates from the wear zones among the sheet metal, rivets, and salt spray particles.

Ultrasonic fatigue tests were performed on Ti60 titanium alloy up to a very high cycle fatigue (VHCF) regime at various stress ratios to investigate the characteristics. The S-N curves showed continuous declining trends with fatigue limits of 400, 144 and 130 MPa at 109 cycles corresponding to stress ratios of R = −1, 0.1 and 0.3, respectively. Fatigue cracks found to be initiated from the subsurface of the specimens in the VHCF regime, especially at high stress ratios. Two modified fatigue life prediction models based on fatigue crack initiation mechanisms for Ti60 titanium alloy in the VHCF regime were developed which showed good agreement with the experimental data.

Effective braking in high-speed trains is one of the major bottlenecks in expediting the technology and possibilities to improve speed. Although substantial progress has been made to increase operating speed, perhaps, thermal fatigue cracking in brake discs is a primary constraint so far. Thermal fatigue cracking is the major cause of brake disc failure in high-speed trains, especially trains with a speed of 350 km/h or above. In this study, new material composition is proposed for brake discs of high-speed trains. A comprehensive investigation is presented based on fatigue crack initiation and propagation, along with wear and micro-hardness characterization. Thermal fatigue tests at various thermal cycles between 20 ℃ and 700 ℃ were performed and the experimental results are compared with fatigue properties of a commercial brake disc material. An experimental trial revealed that thermal cracks normally initiate and propagate along the oxidized grain boundaries; nevertheless, crack propagation is restricted by the fine precipitates and lath structure of martensitic. Moreover, crack length at the initiation and propagation stage is predicted through crack growth rate and favorable grain size in the crack vicinity. Thermal fatigue life can be improved by dictating the microstructure and precipitate morphology of cast steel by tailoring the alloying composition.

Fatigue cracking is a common form of flexible pavement distress, which generally starts and spreads through bitumen. To address this issue, self-healing elastomer (SHE) modified bitumens were elaborated to assess whether these novel materials can overcome the neat asphalt (NA) fatigue performance and whether the current failure definition, failure criterion, and fatigue-restoration criteria can fit their performance. All bitumens were subjected to short-term and long-term aging. Linear amplitude sweep (LAS) test, LAS with rest period (LASH), and simplified viscoelastic-continuum-damage (S-VECD) model were utilized to appraise the behavior of the mentioned bitumens. The results showed that maximum stored pseudo-strain energy (PSE) and tau (τ) × N (number of loading cycles) failure definitions exhibited high efficiency to accommodate the fatigue life of NA and SHE-modified bitumens. Both failure criteria identified that SHE-modified bitumen (containing 1% of SHE) showed the highest increment of fatigue performance (67.1%) concerning NA. The failure criterion based on total released PSE, in terms of the area under the released PSE curve, was the only failure concept with high efficiency (R2 up to 0.999) to predict asphalt binder fatigue life. As well, the current framework to evaluate bitumen self-restoration failed to fully accommodate asphalt binder behavior, because bitumen with higher restoration could not exhibit greater fatigue performance. Consequently, a new procedure to assess this property including fatigue behavior was proposed, showing consistent results, and confirming that SHE-modified bitumen (containing 1% of SHE) exhibited the highest increment of fatigue performance (154.02%) after application of the rest period. Hence, the optimum SHE content in NA was 1%. Furthermore, it was found that a greater number of loading cycles to failure (Nf) did not ensure better fatigue performance and stored PSE influenced the bitumen fatigue behavior.

Structural redundancy acts as a safeguard against localized damage, but it may lead to a variety of potential overall failures. A system-level probabilistic failure path approach is necessary to identify system failure events and account for stress redistribution in structures prone to fatigue-induced damage. Incorporating such probabilistic constraints into a System-Reliability-based Design Optimization (SRBDO) framework comes with a high computational cost. In this study, an innovative method integrates the Branch-and Bound method employing system reliability Bounds (B3 method) and modified Sequential Compounding Method (SCM) to compute the gradient of the system failure probability, particularly those requiring a failure path approach like sequential failure. New compounding rules are introduced in SCM: (a) screening and (b) adaptive compounding to enhance accuracy especially for systems with highly correlated events. This approach allows for the utilization of gradient-based optimizers, offering enhanced computational efficiency in comparison to current gradient-free methods. Additionally, a new bounding rule of the B3 method is introduced to further increase efficiency, and Chun-Song-Paulino (CSP) sensitivity analysis method is used to calculate the derivatives with respect to the design variables. The proposed method is demonstrated through a hypothetical structure of multilayer Daniel’s system and two truss structures of different scales. The semi-analytical formulation of the sensitivity calculation effectively guides the optimization process to the optimum. This new approach accurately calculates the failure probability of the dominant failure sequences and the overall system failure probability as validated by the Monte Carlo simulation. The numerical studies robustly demonstrated efficiency and accuracy of the proposed optimization framework.

Understanding the fatigue behaviors of weld joints is significant in engineering practice. Rotary friction welding (RFW) can join the additively manufactured polymer components. Until now, no research has focused on the fatigue behavior of polymer components jointed via RFW. This study investigates the fatigue life of ABS/PC dissimilar components fabricated via RFW and proposes the fatigue mechanism based on the failure structure. This work uses five different cyclic loads and rotational speeds to investigate the fatigue life. The fatigue life of the RFW of ABS/PC dissimilar rods is better compared with the pure ABS and pure PC specimens due to weld and integrity microstructural changes resulting from the combination of ABS and PC materials. The number of cycles until the rupture of RFW of ABS/PC dissimilar components (y) can be determined by the cyclic load (x) according to the prediction equation of y = −838.25x2 − 2035.8x + 67,262. The fatigue life of the RFW of ABS/PC dissimilar components increase with the increased rotational speed. The number of cycles until rupture (y) can be determined by the different rotational speeds (x) according to the prediction equation of y = 315.21x2 + 2710.4x + 32,124.

In practical design, the question of existence or non-existence of fatigue limit seems little more than an irrelevant academic discussion. Nevertheless, the answer affects many aspects of the fracture mechanics, such as, the calculation of damage accumulation; recognition of the multiplicity of fatigue mechanisms (and consequently, the multiplicity of S–N fields); interpretation of non-propagating cracks; and repercussion on the Kitagawa-Takahashi diagram. Various prestigious scientists deny the existence of a fatigue limit based on the results of failures in very high cycle fatigue (VHCF) regime, far below the high cycle fatigue (HCF) limit. However, the asymptotic extrapolation of the experimental results beyond the scope of testing with S–N models, cannot confirm or deny this hypothesis if those models do not fulfil indispensable physical and statistical requirements. Some phenomenological models based on solid statistical conditions (stability, limit conditions and compatibility), ensure the necessary existence of an asymptotic fatigue limit for each of the possible failure mechanisms. This may or may not be zero according to the experimental results but only the presence of an asymptotic fatigue limit can avoid the absurdity of fatigue failure under zero load value.

The use of composite laminates is characterized by problems such as poor inter-layer bonding and susceptibility of material properties to fatigue cracking, which seriously threaten structural safety. Research on fatigue damage characteristics and fatigue life prediction of fiber-reinforced composites can help to solve such problems. Carbon fiber-reinforced epoxy resin matrix composite laminates are taken as the object of this study. By analyzing the fatigue failure process and the fatigue failure micromorphology of the specimen, the primary damage forms and fatigue damage characteristics of its fatigue failure were obtained. The fatigue failure process of fiber-reinforced composites was simulated using finite element analysis software ABAQUS and its UMAT subroutine function. The tensile–tensile fatigue damage characteristics and failure mechanism of fiber-reinforced composites were studied, and the fatigue life of the composites was predicted. The feasibility of this life prediction method was verified by comparing it with experimentally obtained damage processes and fatigue lives. This intuitive and reliable life prediction method has good research potential for predicting the fatigue limit of fiber-reinforced composites.

A full understanding of bitumen fatigue cracking behavior is extremely important as this phenomenon has a considerable influence on bituminous pavement performance. The current framework for assessing this asphalt binder property is inconsistent in ranking bitumen fatigue performance in terms of the failure definition and damage characteristic curve (DCC) analysis. This study used four different types of asphalt binders: neat asphalt (NA), self-healing thermoplastic polyurethane (STP)-modified bitumen, self-healing poly (dimethyl siloxane) crosslinked with urea bond (IPA1w)-modified bitumen, and styrene–butadiene–styrene (SBS)-modified bitumen (SBSB). All the bitumens were subjected to short-term and long-term aging, and they were also tested by utilizing the linear amplitude sweep (LAS) test and the simplified viscoelastic continuum damage (S-VECD) model. LAS and S-VECD procedures were used to apply the newly proposed and current frameworks in order to analyze bitumen performance. The current framework showed that the bitumens that used a higher number of loading cycles (N) to reach their failure points (Nf) failed to exhibit greater fatigue performances in terms of DCC analysis. The developed framework (mainly based on the damage intensity [S] instead of N) was used to solve the inconsistency between the failure definition and DCC assessment in ranking bitumen performance. Additionally, the current framework (failure criterion) presented two R2 values below 0.1, but the developed framework (failure criterion) showed that all R2 values were greater than 0.9. The developed framework represents a turning point because, for the first time, this type of procedure is mainly being based on S instead of N. Although further tests are needed to confirm its efficiency, it eliminates the inconsistency between the failure definition and DCC assessment.