Fatigue & Fracture of Engineering Materials & Structures最新文献

Red clay is highly susceptible to cracking due to its nature, and the reduction in strength caused by cracking can lead to engineering disasters. To investigate the cracking sensitivity of red clay, a homogeneous fracture model of red clay based on the cohesive zone model was established using ABAQUS in this work, the reliability of the model was verified through a three-point bending test, and then the crack propagation process and sensitivity to test factors of red clay were further analyzed. The results show that the fracture simulation of the cohesive zone model is in good agreement with the test results, confirming by the high reliability. The depth of prefabricated cracks and fulcrum spacing had the significant effects on the crack path, and the decrease of prefabricated crack depth and fulcrum spacing led to the increase of critical load. Meanwhile, the loading rate had little effect on the load–displacement curves.

The reloading characteristics of slope projects such as water conservancy and hydropower in cold regions after excavation and unloading are the key to the long-term stability problem of bank slopes in reservoirs. After pre-peak unloading and freeze–thaw, uniaxial gradient loading creep test was carried out with marble, and the unloading creep mechanical behavior of marble under different temperature ranges and different numbers of freeze–thaw cycles was studied. The results show that the temperature range of freeze–thaw and the number of cycles control the reduction of creep damage stress and long-term strength as well as the increasing trend of creep strain of marble, and the time-mechanical response of unloaded marble under the action of freeze–thaw with large temperature difference is more obvious. Based on the traditional Burgers model, a non-constant Burgers model considering freeze–thaw damage was proposed, and the applicability and rationality of the model were verified.

This study investigates the impact of various surface finishes on the low cycle fatigue (LCF) properties of laser powder bed fusion GRCop-42. The evaluated surfaces include as-built, machined, and chemically polished finishes (1.0% and 2.0% ranges). LCF life of polished GRCop-42 was assessed at cryogenic (−195°C), ambient, and elevated temperatures (200°C, 400°C, 600°C, and 800°C) across three strain ranges. Results indicate that surface finish has minimal impact on LCF life. Stress across different strain levels showed minimal effect of surface finish on cyclic hardening/softening. Cryogenic temperatures led to cyclic hardening followed by stabilization, while ambient and 200°C temperatures showed initial hardening followed by softening. At 400°C and above, specimens displayed continuous cyclic softening. Fractography showed that surface finish impacts plastic deformation: as-printed and polished surfaces had brittle fractures, while machined specimens were ductile. Specimens at cryogenic and ambient temperatures exhibited brittle fractures, whereas those at elevated temperatures showed plastic deformation and microcracks.

Carbon fiber–reinforced foams (CFRFs) are expanded thermoplastic composite materials reinforced with three-dimensional discontinuous carbon fibers. Herein, the effects of their unique internal structure on fatigue properties were investigated. Through tension-tension fatigue tests and the digital image correlation (DIC) method, distinct stiffness reduction behavior was observed across the entire specimen and at the fracture points. The results suggest that local stiffness reduction behavior affects the fatigue properties. From the DIC method, damage was observed by scanning electron microscopy and the fiber tortuosity, and the void fraction were quantified using X-ray computed tomography scans. In the case of three-dimensional oriented fibers, stress was concentrated at fiber ends, fiber intersections, and bent fibers, resulting in fiber pull-outs and matrix cracks. In the case of voids, the void size affected damage development, and the stress concentration around the voids caused fiber fracture and matrix cracks.

The work investigates nonvalidity of the common presumption that the nondamaging cycles do not influence residual fatigue life. Paradoxically, application of the full loading spectrum (more cycles) resulted in approximately 2.3 times longer life of the fatigue crack growth specimens than application of the spectrum with 33% of the smallest amplitudes omitted. Unlike in humid air (controlled relative humidity of 50% at 23°C), the effect disappeared in a dry-air chamber (relative humidity <10% at 23°C), where both fatigue lives were short. The mechanism responsible for these effects was identified as the oxide-induced crack closure, an extrinsic mechanism unrelated to material damage. Oxide debris developed on fracture surfaces was observed by light and scanning electron microscopy, whereas crack closure was measured during the experiments. The presented counterintuitive behavior in humid air may result in wrong assessment or prediction of components residual fatigue lives, which can be nonconservative in some scenarios.

To accurately characterize the heat dissipation behavior of LF6 aluminum alloy laser arc composite welded joint under low cycle fatigue, two fatigue life prediction methods based on dissipated energy were proposed. The experimental investigation has revealed four stages in the evolution of surface temperature increment, including initial temperature increase, subsequent decline, attainment of thermal equilibrium, and sudden temperature escalation leading to failure. Based on the energy dissipation method, two models predicting lifespan of welded joints have been formulated. Model I incorporates the effects of stress amplitude and mean stress, on lifetime demonstrating a strong linear correlation particularly under high-stress level according to experimental comparisons. Model II introduces a relationship between plastic strain amplitude and inherent dissipated energy to assess fatigue life of welded joints. Digital imaging correction technique has been utilized to quantify plastic strain amplitude. The predicted results from Model II agree well with experimental data.

The investigation of the tensile properties of rock materials is essential for understanding the failure mechanism of engineering rock masses. In this study, we conducted a series of Brazilian splitting tests on granite specimens under three different loading rates, concurrently monitored using acoustic emission (AE) and digital image correlation (DIC) techniques. The results show that the mechanical parameters of granite disks are positively correlated with the loading rate. The AE waveforms are found to be associated with the lower frequency band, suggesting that this frequency range primarily dominates the failure mechanism in granite disks. Furthermore, the onset of micro-tensile fractures precedes the development of micro-shear ones. The elevation distribution of the fractured surfaces of the granite disks follows a Gaussian function. The fractal dimension increases progressively with the loading rate, whereas the complexity and irregularity of the fractured surface decrease. Moreover, the cracking mechanism of granite disks at the microscale was revealed using grain-based modeling (GBM). The intergranular tensile cracks predominantly form along the radial direction, and the proportion of intergranular shear cracks is the smallest.

In fatigue evaluation of welded structures, explicit weld representations in finite element (FE) models are needed for reliably capturing stress or strain concentration behaviors at critical weld locations, for example, weld toe or weld root, in using widely accepted traction structural stress or extrapolation hot-spot stress methods. The laborious efforts needed for generating weld geometry have been a major challenge for fatigue evaluation of complex structures containing many welds. In this paper, we present a user-defined fillet-weld element formulation and its numerical implementation for computing traction mesh-insensitive structural stresses. The fillet-weld element is formulated by connecting several linear four-nodes Mindlin shell elements around weld region as a user-defined element. The resulting elements can be directly used with major commercial FE codes through an available user subroutine interface. A number of well-documented fillet-welded components are then used for validating the accuracy and robustness of the developed fillet-weld elements.