Fatigue & Fracture of Engineering Materials & Structures最新文献

Current research on frost heave-induced cracking in fractures of rock masses in cold regions typically assumes that fractures are fully saturated. However, in actual engineering practice, rock mass fractures are often in an unsaturated state. Upon freezing, the fracture surfaces are subjected to a complex combination of gas pressure, freezing pressure, and ice friction forces. This study investigates the crack initiation mechanisms of unsaturated rock fractures with asymmetric edge cracks under gas-ice pressure conditions. Assuming a small yield range, we derive the calculation formulas for gas pressure after freezing, stress intensity factor, crack initiation angle, and crack initiation stress based on the complex variable function and elastic-plastic crack mechanics theory. Additionally, an improved phase-field model is proposed for calculating dynamic crack propagation in mixed-mode I-II fractures, with key parameters analyzed and discussed. The results demonstrate that: By comparing the analytical solutions with numerical calculations, the validity of the proposed model is verified. During the freezing process, dynamic crack propagation in unsaturated fractures will exhibit bifurcation. At higher water saturation levels, crack propagation shows a pattern of initial bifurcation followed by subsequent merging.

This research used 30%, 40%, 50%, and 60% coarse aggregates and 0.15%, 0.3%, and 0.45% wavy steel fibers to make end-notched disc bend self-compacting concrete specimens for calculating and comparing flexural cracking toughness index by ASTM C1609, JSCE SF-4, and JG/T 472-2015 methods under pure modes I and III. The variation trends of different procedures under pure mode I was more affected by coarse aggregates and fibers had no noticeable influence. But under pure mode III increasing both fibers and aggregates improved the flexural cracking toughness. The estimation of JG/T 472-2015 method was better than other methods under pure mode I. In pure mode III, due to positive effect of fibers on the pre-peak, peak, and post-peak areas, the deflection exceeds 1 mm. Hence, calculating the area under the load–displacement curve is facilitated for the ASTM C1609 and JSCE SF-4 methods up to L/150 deflections.

The primary goal of this systematic literature review is to identify, characterize, and make a comprehensive analysis of the available research on the fatigue strength of additively manufactured (AMed) metal materials when subjected to loading cycles that exceed the preconceptualized fatigue limit ($��{10}^7�$ cycles) and the very high cycle fatigue (VHCF) regime. Considering the inherent complexity and magnitude of influential variables present in AM metal processes, this paper explores in-depth the relevant conclusions taken by theoretical/experimental studies and their respective results of several AMed materials in the VHCF regime. The present review focuses on key research topics of metal AM fatigue strength, such as crack initiation and failure mechanisms, examining the influence of microstructure and defects, the effect of the input process parameters, postprocessing methods, and the influence of testing conditions on fatigue strength.

In this study, molecular dynamics (MD) simulations were employed to investigate the crack propagation behavior of single-crystal titanium with various crystal orientations under cyclic loading. The analysis demonstrates that each crack model displays temporary cyclic hardening and predominant cyclic softening characteristics. The orientation of crack propagation primarily impacts the characteristics of the softening stage, with less influence on the initial hardening stage. A notable orientation correlation is evident in the mechanism of crack propagation, characterized by the presence of various slip modes and deformation twinning (DT) systems. The crack tip deformation behavior obtained from the simulation aligns with the theoretical predictions of linear elastic fracture mechanics (LEFM). The crack growth rate (CGR) and ΔJ for different crack models show good correlation, and both the crack propagation direction and crack plane orientation affect the characteristics of the ΔJ–da/dN curves.

Traditional physical models and purely data-driven approaches often struggle with small sample sizes and the complex effects of strain ratios. To overcome these challenges, this study integrates physical principles with machine learning techniques to improve fatigue life predictions for natural rubber (NR). A uniaxial fatigue test on NR was performed, generating data to construct a physical model. A physics-informed neural network (PINN) model was subsequently developed, utilizing the fatigue life predicted by the physical model, along with engineering strain amplitude and strain ratio as input variables, whereas the experimentally observed fatigue life served as the output variable. The accuracy of the physical model, a data-driven model, and the proposed PINN model was evaluated by comparing their predictions against measured fatigue life data. The findings demonstrate that the PINN model significantly enhances prediction accuracy, with its fatigue life estimates consistently falling within 1.5 times the measured values.

Under vibration conditions, continuous alternating loads cause fatigue damage to structures, affecting their stability, durability, and overall safety. In this paper, the additional damping structures with entangled metallic wire material (EMWM) is proposed. Dynamic tests with different loading frequencies and loading amplitudes are carried out to evaluate the energy dissipation and stiffness characteristics of the different structures in terms of energy dissipation, loss factor, and average stiffness. Fatigue tests are conducted, and the fatigue life tests are applied with different loading amplitudes and loading frequencies using displacement control, and the fatigue properties are obtained under different numbers of cyclic loading. The test results are analyzed with respect to the energy dissipation mechanism of EMWM and the characteristics of the additional damping structure. The hysteresis curves under different loading times are identified by parameters, and the fatigue mechanical models are constructed. Comparison between the predicted data of the model and the hysteresis curve data of the test indicates that the model has high accuracy.

An approach to the analysis of the influence of impact loading on creep, accumulation of hidden damage and fracture of structural elements made of functionally graded materials (FGM) is proposed. The approach is based on the analysis of additional damage caused by the impact loading and the stress redistribution caused by it. For the numerical modeling, finite element analysis was applied using algorithms for determining the size and direction of motion of macroscopic defects by means of the analysis of the time-varying damage field. The fracture after an impact on a beam made from FGM is considered. The nature of fracture of a beam made of two-layer metal-ceramic material was studied. The advantages of using FGM to ensure a better long-term response of a structural element to a non-destructive impact loading are shown. An approach to determine the time until the complete fracture of the FGM beam by the simultaneous description of the motion of two cracks is proposed.

The brake control box beneath an EMU is exposed to dynamic and fluctuating load cases, increasing its susceptibility to vibration fatigue failure. A novel lightweight design approach was implemented to integrate structural and material optimizations. Static and fatigue tests of the T700/5429 CFRP were carried out to augment the stress analysis and predictions of the vibration fatigue life. The local stresses perpendicular and parallel to the welds were obtained to calculate the stress ratio, stress range, and allowable stress value corresponding to the stress component. The fatigue strength of the aluminum box was estimated on the basis of multiaxial criteria, and the fatigue life of the two boxes was predicted with Dirlik's theory. These computational findings unequivocally indicated a noteworthy reduction in damage to the composite box subsequent to lightweight modification, thereby successfully satisfying both the stiffness and strength criteria essential for the safety and reliability of the EMU.