Mechanical properties and damage constitutive model of tuff under stress–seepage coupling during low-temperature curing

Dynamic tensile failure of CFRP/aluminum bolted joints: Experimental and numerical investigation

The dynamic tensile failure of composite/metal bolted joints is governed by the coupled effects of stress concentration, local contact deformation, and rate-dependent damage evolution. In this study, single-bolt CFRP (Carbon Fiber Reinforced Polymer)/7075 aluminum joints are found to exhibit a pronounced strain-rate strengthening effect, with the peak stress increasing from 438.18 MPa at 1000 s −1 to 579.29 MPa at 3000 s −1 . Using split Hopkinson tension bar tests with high-speed imaging, damage was consistently observed to initiate around the composite bolt hole and became increasingly localized as the strain rate increased. More importantly, the combined high-speed observations and numerical results suggest that the local failure morphology under high-strain-rate loading is closely associated with transient secondary bending and bolt tilting, which intensify compressive damage in the region perpendicular to the loading direction and thus influence the evolution of hole-edge damage. An Abaqus/Explicit model based on the three-dimensional Hashin failure criterion was developed. The model predicted the peak stress with an error of 4.08% and successfully reproduced the main damage evolution features. These results provide new insight into the rate-dependent local failure mechanism of composite/metal bolted joints and offer a useful basis for the design and assessment of impact-resistant hybrid joint structures.

The failure characteristics of heat-treated sandstone subjected to splitting loading and the pore-crack distribution effects

Mechanical properties and failure characteristics of granite with non-through cracks under thermal cycling.

Thermal cycling and pre-existing cracks significantly influence the mechanical response and damage evolution of granite in high-temperature rock engineering. To clarify their coupled effects, granite specimens with different prefabricated crack inclination angles (0°, 45°, and 90°) were subjected to different temperature conditions (30-130 °C) and thermal cycle numbers (1-5 cycles), followed by uniaxial compression tests. Characteristic stresses, AE (AE) parameters, AE b-value evolution, fractal dimensions, macroscopic failure patterns, and SEM observations were jointly analyzed to reveal the damage mechanism.The results show that the mechanical and AE responses of cracked granite exhibit clear nonlinear dependence on temperature, thermal cycle number, and crack inclination. Under the same crack inclination, the peak stress, crack initiation stress ratio, AE counts, and cumulative AE energy vary non-monotonically with temperature, and 70 °C appears to be a critical transition temperature for AE activity and damage evolution. Increasing the number of thermal cycles promotes damage accumulation, enhances AE activity, and advances the abrupt drop point of the AE b-value, indicating earlier dominance of large-scale crack propagation and main crack formation. The prefabricated crack inclination further controls the crack propagation path and failure pattern. In particular, 45° cracks are more likely to guide inclined crack coalescence and tensile-shear failure under intensified thermal cycling, whereas 90° cracks tend to maintain tensile-dominated failure. SEM observations and box-counting fractal analysis further confirm that thermal cycling promotes the development of pores and microcracks, especially at 50 °C, 100 °C, and 130 °C. These findings provide a multi-scale understanding of the coupled thermal-mechanical damage mechanism of cracked granite and may support stability evaluation of rock masses subjected to repeated thermal disturbance.

Numerical Analysis of High-Temperature Tensile and Compressive Creep in Cast Irons: Local Effects of Microstructure

Cast irons are extensively used in high-temperature applications such as cylinder heads of heavy-duty diesel engines, where sustained exposure to high stresses and temperatures can initiate creep-related failure mechanisms, impacting their long-term durability and efficiency. Our previous experimental research demonstrated significant differences in creep mechanisms and behaviour of compacted graphite iron (CGI) under tensile and compressive loading. In situ analysis of the microstructural effects defining these differences during long-term high-temperature experiments is hardly possible. An alternative way to study these effects is to develop advanced micromechanical models using a finite-element method. The aim of this paper is to study the local responses at microscale (considering local distributions of stresses and strains) to macroscale long-term loading at high temperature employing direct introduction of microstructural features into numerical models. The models consider elasto-visco-plastic behaviour of the CGI material under tensile and compressive loading regimes. The novel results presented in this paper are applicable to cast irons as well as other heterogeneous materials such as metal matrix composites and the models presented can be used as a tool in the development of materials with microstructures customised for high-temperature applications.

Experimental investigation on damage and seepage characteristics of layered slate under cyclic loading and unloading of stress

To investigate the damage deterioration and seepage evolution of bedded slate under cyclic axial loading–unloading, triaxial tests were conducted on specimens with bedding angles of 0°, 30°, 45°, 60° and 90° under 10 MPa confining pressure and 5 MPa pore pressure. The study systematically analyzed the influence of bedding structure on rock strength, deformation, damage accumulation, and permeability. Consequently, a damage constitutive model and a permeability evolution model were developed, incorporating bedding angle, cyclic fatigue, loading path, and effective stress. Results indicate that bedded slate exhibits pronounced nonlinear deformation, hysteresis, and stiffness degradation under cyclic loading, with responses strongly dependent on bedding angle. Peak strength follows a “U-shaped” distribution, where specimens near 45° show the greatest damage due to combined shear-tensile failure along bedding planes. Permeability initially decreases due to fracture compaction but subsequently increases as stress exceeds the historical maximum, facilitating fracture interconnection. This evolution shows distinct anisotropy; intermediate bedding angles promote more efficient seepage channel formation, leading to larger permeability increments. The proposed models accurately reproduce the experimental stress–strain and permeability behaviors across different angles. These findings provide a theoretical framework for stability analysis and seepage hazard mitigation in stratified rock masses subjected to cyclic disturbances and fluid flow.

Failure evolution and strength modeling of H-jointed layered sandstone under compression

H-shaped joints, which consist of tensile and shear parts, are common in layered rocks and substantially affect rock failure and instability. To explore the mechanical performances of the H-jointed sandstone under different loading conditions. Uniaxial and confined compressive tests were carried out on H-jointed sandstone samples. The samples’ stress-strain responses, failure modes, AE activities, and strength were analyzed. The results show that the stress-strain curve has four phases: crack closing, elastic phase, elastic-plastic phase, and residual stages. The failure patterns of the H-jointed samples change from tension to shear as the joint dip angle increases. Tensile failure is dominant at lower inclination angles, whereas shear slip failure occurs along the joint surfaces at higher angles. Sliding along the joint surfaces with tensile cracking is observed at moderate angles. The joint roughness coefficient (JRC) significantly influences the samples’ mechanical behavior. A modified Hoek-Brown criterion that considers the joint dip angle and JRC is suggested for evaluating the strength of H-jointed rock samples under compression. This study provides a better understanding of the mechanical performance of H-jointed sandstone and a method to evaluate the strength.