Fatigue & Fracture of Engineering Materials & Structures最新文献

Residual fatigue life prediction of passenger car brake friction plates under emergency braking is considered important for vehicle safety. The multiphysics coupling among temperature, stress, and wear is often not represented in a unified way. An integrated prediction framework is proposed. The framework combines a three-dimensional finite element thermomechanical wear simulation, an improved Archard wear law, and the Taguchi quality loss model in present value form. The finite element model describes transient frictional heating, contact stress evolution, and wear accumulation in a ventilated disc brake during emergency braking. The wear volume time response is produced by the simulation. A cubic polynomial wear law is identified from the simulated response and is incorporated into the service quality loss model to represent the triphasic wear evolution and the performance degradation of the friction plates. Stochastic service life and residual life distributions are obtained by applying cumulative failure functions together with the quality loss formulation. The framework can provide a quantitative basis for analyzing how design tolerances, manufacturing deviations and service conditions influence fatigue life, and can support planning of preventive maintenance and reliability improvement for brake friction plates.

This study investigates the fatigue degradation mechanism of ultra-high-performance concrete (UHPC) in nearshore wind turbine towers under the time-sequential effects of wind-induced fatigue and chloride erosion. Through a comprehensive experimental program, UHPC specimens were subjected to initial fatigue loading, chloride erosion, and secondary fatigue loading (up to 2 million cycles). Results show that chloride ion concentration peaks in the mid-span tensile zone and decreases with depth and distance. Initial fatigue damage significantly increases diffusion by forming microcrack networks. Scanning electron microscopy (SEM) analysis highlights severe steel fiber corrosion, interfacial debonding, and pullout damage, driven by fatigue–chloride interaction, which reduces fiber bridging capacity and accelerates fatigue damage. A chloride diffusion model based on Fick's second law was developed, achieving an average prediction error of 5.10%–8.93% against experimental data. Additionally, a modified fatigue damage model incorporating a “fatigue–erosion” time-sequential damage index was proposed, conservatively enveloping experimental damage curves. The findings underscore the synergistic deterioration from fatigue-induced cracking and chloride corrosion, providing critical insights for enhancing the durability design of UHPC in chloride-rich coastal environments.

This study investigates the fatigue degradation mechanism of ultra-high-performance concrete (UHPC) in nearshore wind turbine towers under the time-sequential effects of wind-induced fatigue and chloride erosion. Through a comprehensive experimental program, UHPC specimens were subjected to initial fatigue loading, chloride erosion, and secondary fatigue loading (up to 2 million cycles). Results show that chloride ion concentration peaks in the mid-span tensile zone and decreases with depth and distance. Initial fatigue damage significantly increases diffusion by forming microcrack networks. Scanning electron microscopy (SEM) analysis highlights severe steel fiber corrosion, interfacial debonding, and pullout damage, driven by fatigue–chloride interaction, which reduces fiber bridging capacity and accelerates fatigue damage. A chloride diffusion model based on Fick's second law was developed, achieving an average prediction error of 5.10%–8.93% against experimental data. Additionally, a modified fatigue damage model incorporating a “fatigue–erosion” time-sequential damage index was proposed, conservatively enveloping experimental damage curves. The findings underscore the synergistic deterioration from fatigue-induced cracking and chloride corrosion, providing critical insights for enhancing the durability design of UHPC in chloride-rich coastal environments.

This study investigates fatigue damage evolution in TC17 titanium alloy under residual stress using acoustic emission (AE), scanning and transmission electron microscopy. The compressive residual stress sample U1 exhibits approximately 19% longer fatigue life than stress-free U1R. Fractography shows U1R is dominated by tearing ridges and secondary cracks, whereas U1 features slip steps and intersecting slip planes. During crack propagation in segments A (A1/2) and B (B1/2), U1 displays ~50% shorter average secondary crack length and ~40–51% lower crack density than U1R, indicating that compressive residual stress critically regulates dislocation activities—multiplication, sliding, and activation. In U1R, multiplication and activation occur concurrently with activation dominant; in U1, sliding predominates followed by activation due to reduced stress intensity at crack tips. Dislocations accumulate at grain boundaries and activate under cyclic loading. Based on variations in dislocation activities, configurations, and AE signals at crack stages, this study proposes an integrated AE-microdamage characterization method.

This study investigates the fatigue strength of an “L”-shaped bolted joint structure subjected to complex loads on a specific aircraft model. Through the design of experiment specimens, finite element simulations, fatigue experimenting, and theoretical analysis, a comprehensive evaluation of the structure's fatigue performance was conducted. Finite element analysis was employed to simulate the stress–strain distribution and load transfer characteristics under various loading conditions. Fatigue experiments were then performed to validate the simulation results and assess the fatigue life under specific service scenarios. The results revealed that stress concentration at the bolt hole edge is the critical site for fatigue crack initiation and the primary cause of structural failure. A comparative analysis using the Design Fatigue Rating (DFR) method demonstrated good agreement between experimental data and theoretical predictions, confirming the method's applicability. Additionally, the length of the aluminum alloy plate and the magnitude of the applied load had minimal impact on the inherent fatigue performance, while reducing stress concentration at critical locations significantly improved fatigue life.

This work focuses on studying the corrosion fatigue characteristics of Cr-Ni-Mo-V gun steel under high-temperature and high-pressure propellant gas cyclic loading. Using a pressure vessel–based high-temperature and high-pressure erosion experimental device, experimental research was conducted to analyze the thermochemical erosion mechanisms and fatigue behavior of gun steel under cyclic high-temperature gas loading at 194 and 256 MPa, respectively. The findings reveal that the erosion of gun steel under propellant gas constitutes a transient process. In such environments, the gun steel specimen develops a surface white layer under the combined action of pressure, thermal stress, and gas corrosion. The thickness of this white layer exhibits a positive correlation with both the number of erosion cycles and the gas pressure. Specifically, the white layer thickness ranges from 2.03 to 3.04 μm at 194 MPa and from 3.69 to 4.26 μm at 256 MPa. In the upper portion of the white layer, large-size cracks are observed, whereas a continuous microcrack layer emerges at the base. The white layer contains C, O, and S as the primary impurity elements, with C exhibiting the highest concentration and an interspersed distribution. The distribution of O and S demonstrates distinct stratification. With an increase in the number of erosion cycles, the large-size crack distribution area expands, accompanied by a growth in the thickness of the basal microcrack layer. Both the thickness of the S-rich layer and the O-rich layer increase.

The quasi-static shear mechanical behavior and damage mechanisms of high-silica woven fiber-reinforced phenolic interfaces after thermal-oxidative aging and fatigue were investigated through shear tests in conjunction with digital image correlation (DIC) and scanning electron microscopy (SEM). The residual shear strength of interface progressively decreases with increasing fatigue amplitude, cycles, and duration of thermal-oxidative aging. Up to 20,000 cycles, the residual strengths under fatigue loadings $�10�\%�{\tau }_b$, $�20�\%�{\tau }_b$, $�30�\%�{\tau }_b$, and $�40�\%�{\tau }_b$ decreased by 8.9%, 12.9%, 21.3%, and 30.3%, respectively. At fatigue amplitude $�30�\%�{\tau }_b$, thermo-oxidative aging for 36, 76, and 103 days caused reductions of 30.4%, 34.6%, and 38.4% relative to the unaged specimens. DIC and SEM reveal that interfacial shear damage initiates at defects along the biphasic interface, progresses through microcrack propagation with concurrent penetration into the interlaminar region, and ultimately results in crack coalescence and macroscopic delamination-induced instability failure. Under fatigue-dominated loading, damage is characterized by fiber fracture and interlaminar debonding, whereas thermo-oxidative aging suppresses fiber tearing but markedly exacerbates interlaminar debonding. Based on the equivalence principle of residual strength under fatigue loading-cycling-aging, a predictive model for residual shear strength was developed to account for the effects of thermal-oxidative aging and fatigue. Experimental validation showed that the model achieved an average relative error of approximately 10%, demonstrating good agreement with the measured data.

Selective laser melting (SLM) enables the fabrication of complex metal components but poses challenges due to fatigue failure under cyclic loading. This study investigates fatigue crack growth (FCG) in SLM C300 margining steel using compact tension (CT) specimens built in X, Y, and Z directions, tested per ASTM E647 with a constant load ratio (R = 0.1). Monotonic tests revealed direction-dependent yield stress, with X being highest and Y lowest. To predict fatigue crack growth rate (FCGR) and stress intensity factor (SIF), five nonlinear regression models were evaluated. Given the nonnormal distribution of FCGR and SIF, the models were refined using load ratio (R = P_min/P_max) and stress intensity factor ratio (R_k = (ΔK)_min/(ΔK)_max). Locally weighted regression (LWR) achieved the highest accuracy, followed by polynomial and hyperbolic tangent regression. Logistic regression improved at higher SIF values, whereas power regression, despite aligning with Paris' law, performed poorly. Model choice and material properties are crucial for reliable FCG prediction in SLM components.

AA7075-T6 aluminum alloy panels with damaged and thick surface layers were examined for their fatigue life with composite patches. Simulations using finite element software were conducted to analyze stress and crack propagation stages. Two models of uniform and skew crack fronts fatigue crack growth were implemented by combining XFEM and VCCT methods on the plates repaired with composite patches based on the Paris equation. The available experimental results and numerical simulation results are strongly correlated according to the comparison. To determine fatigue crack propagation path and fatigue crack propagation life, XFEM and VCCT simulation methods can be used for cracks in thick panel repairs with composite patches. In addition, the Paris equation can be used to determine fatigue cracks propagation path and fatigue crack propagation life. An increase of over 317% in fatigue life was achieved by applying composite patching to the cracked thick panels in the study. Based on the experimental results, the fatigue crack growth curve of the skew crack front model was similar to those obtained by the conventional uniform crack front models; however, the skew crack front fatigue life prediction was more accurate. This study specifically focused on evaluating crack propagation behavior in thick panels with single-sided composite patches, which represents a common but challenging repair configuration in aerospace applications.