Fatigue & Fracture of Engineering Materials & Structures最新文献

The high load with very low occurrence probability in the fatigue load spectrum may introduce the favorable residual stress at the metal structure notch, so it is necessary to clip the high load of spectrum to avoid a dangerous test result. Based on the time-domain extrapolation principle and the extreme value theory, the probability distribution of high load in the whole-life load spectrum was predicted. Considering the dispersion of high load and the influence of high load on the structural fatigue life, a selection criterion of high load clipping level was proposed, which makes the test result under the corresponding clipped spectrum both conservative and authentic. To demonstrate the rationality and practicality of criterion, the transport aircraft load spectrum was extrapolated and the spectral fatigue tests of 2024-T3 aluminum alloy sheet were conducted, providing reference for the design of fatigue test load spectrum of aircraft structure in practical engineering.

The tension–torsion multipath cyclic loading experiments of the nonlinear viscoelastic adhesive bonding butt joints were conducted with the asymmetric strain-control mode, and the effect of loading path and strain strength on the mechanical behavior of the joint was observed through the dissipated energy and the cyclic stress response. It was found that the loading path had influences on the fatigue damage and nonproportional strain loading path had additional fatigue damage to the joints. Meanwhile, the initial decline rate of dissipated energy and cyclic stress increased with the increase of equivalent mean strain (EMS) and equivalent strain amplitude (ESA) have been observed. In addition, the uniaxial cyclic damage model was extended to a tension–torsion fatigue damage model by adding a path factor into the tensile and torsional cyclic damage model. The model calculated results showed that the proposed model could better predict the loading path–dependent fatigue behavior of the joint.

The high-cycle tension–compression fatigue property of 1.0%C–1.5Cr% bearing steel with niobium (Nb) content of 180 and 800 ppm was investigated. The results indicated that the fatigue limit for both Nb-free and 0.018% Nb steel remained at 900 MPa, while 0.080% Nb steel increased to 950 MPa. Furthermore, Nb played a dual role in the high-cycle fatigue limit. First, it refined the undissolved carbides. In 0.080% Nb steel, the dissolution of rod-like carbides resulted in a 31% reduction in the size of undissolved carbides compared with Nb-free steel, and the roundness was increased with carbide aspect ratio decreasing from 1.37 to 1.16. Second, the stress field generated by the tip-shaped TiN crack source in 0.018% Nb steel exceeded that produced by the spherical oxide inclusions in Nb-free steel and the ellipsoidal NbC in 0.080% Nb steel, which negatively impacted the fatigue properties of the steel.

This work examines the effect of loading rate ($��\stackrel{·}{K}�$) on the mode III fracture behavior of sandstone. Edge-notched diametrically compressed (ENDC) disc sandstone specimens were tested under different static and dynamic mode III fracture loadings, revealing a clear loading rate effect on both mode III and mode I fractures. Specifically, the peak load and fracture toughness (K_IIIC, K_IC) increase as the $��\stackrel{·}{K}�$ increases across both static and dynamic scales. At the static scale, the K_IIIC is about 1.28–1.38 times of the K_IC, whereas at the dynamic scale, the K_IIIC is less than the K_IC. The relationship between K_IIIC and K_IC is affected by the loading scale and the shape of the specimen, but the data collected thus far indicate that the origin and type of rock have minimal effect on this relationship. In addition, the fracture surface morphology characteristics were quantitatively analyzed.

The enhanced fatigue resistance of superelastic Cu-Al-Mn shape memory wires was investigated via a bamboo-like grain structure obtained by cyclic heat treatment (CHT). Our findings reveal that increasing the number of CHT cycles facilitates grain growth, and the grain boundary will change from a brittle triple junction to a stronger straight grain boundary. This structural feature of grain boundaries alleviates stress concentration effects on dislocation motion. In particular, the 5CHT and 7CHT samples displayed negligible residual strain after 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 5CHT cycles exceeds 4650 cycles at 5% strain, which is more than five times that of the traditional polycrystalline quenched sample.

Lugs serve as crucial linkages in aircraft structures to connect components and transmit loads and motions. Because of their mechanical functions, their failure would lead to severe consequences. To ensure structural safety, factors that could affect the fatigue performance should be well considered and quantified. In this paper, the effects of the inevitable friction and clearance between the lug and load pin are quantified. The fatigue lives of straight and oblique lugs are predicted by using the classical local stress approach and a modified theory of critical distances. Satisfactory correlations between the predictions and extensive experiments are achieved.

The results of testing resistance welded joints using double lap shear (DLS) specimens are presented. The welded joints of polyetheretherketone reinforced with carbon 5-harness satin weave (CF/PEEK) were made using two steel meshes with wire diameters of 0.04 mm and 0.1 mm. Additionally, the impact of welding with thin glass fabric (48 gsm) as an electrical insulator on joint strength was investigated. The specimens with selected process parameters were then fatigue-tested at various percentages of their static shear strengths at a load ratio R = 0.1 and frequency f = 10 Hz. The performances of resistance welded DLS-B specimens were compared with the current state of art, especially in the context of the use of SLS specimens. The failure modes of the specimens were presented, and a linear stress-life (S–N) curve was drawn and analyzed.

With the wide application of large wall-thickness metallic structures in engineering, there has been a growing focus on the three-dimensional fracture issues associated with these materials. This article uses the phase-field model to investigate the impact of thickness on elastic–plastic metallic materials. Initially, the fracture toughness of metallic materials in three dimensions is calculated under elastic deformation. The findings reveal that the outcomes obtained from the phase-field model remain consistent regardless of thickness, thus confirming its effectiveness. Subsequently, the study delves into the three-dimensional fracture behavior of metallic materials during plastic deformation. It illustrates how the phase–field model approach enables a thorough simulation of crack propagation within these materials, offering a comprehensive understanding of their fracture behavior. By analyzing the phase-field contour, the thickness effects of three-point bending specimens during crack growth are effectively captured. In addition, the dimensionless fracture toughness ratio trends with thickness are compared between phase-field modeling and experimental results in the open literature, showing good agreement.