Macro- and micro-scale mechanical properties and energy evolution analysis during unidirectional freeze-thaw cycling of sandstone.

Fracture behavior and constitutive modeling of rock-concrete contact surfaces with different roughness under freeze–thaw cycles

Strength Degradation of Sandstone Under Coupled Loading and Freeze–Thaw Cycles: Experimental Study and Discrete Element Numerical Simulation

Previous studies have mainly examined sandstone freeze–thaw degradation under unloaded conditions, whereas the continuous influence of sustained stress on compressive and tensile properties remains unclear. To address this issue, water-saturated specimens were subjected to axial loads of 0–2 MPa and 0–10 freeze–thaw cycles, followed by uniaxial compression and Brazilian splitting tests. A two-variable exponential strength model and a load–freeze–thaw coupled discrete element model were established. Both strengths decreased with increasing freeze–thaw cycles. Under no load, after 10 cycles, the uniaxial compressive strength and tensile strength decreased by 27.85% and 36.67%, respectively, indicating higher freeze–thaw sensitivity of the tensile property. Loading mitigated strength loss: after 10 cycles, the two strengths of the 2 MPa group were 9.59% and 10.53% higher than those of the no-load group. The retention effect on compressive strength first increased and then decreased, whereas that on tensile strength increased with cycle number. The discrete element results showed that frost-heave cracks evolved from local initiation to connection and clustering, with tensile cracks dominating. Loading reduced tensile bond breakage and slowed crack accumulation and subsequent coalescence, linking the observed strength retention to the inhibition of mesoscopic tensile damage.

Experimental study on uniaxial compression mechanical properties and fracture fractal characteristics of dense sandstone under different temperature conditions

Shear strength and damage model of silty sand in Daxing 'anling under freeze-thaw cycles.

This study examines the evolution of mechanical properties of silty sand from the Daxing' anling region under coupled freeze-thaw cycles and confining pressure, using triaxial testing. The results show that at low confining pressure and with zero or limited freeze-thaw cycles, the stress-strain response exhibits strain softening, indicative of brittle failure. In contrast, at high confining pressure or after multiple freeze-thaw cycles, the behaviour transitions to strain hardening, characterised by plastic failure. Freeze-thaw cycling markedly degrades the soil's mechanical performance. The first cycle causes a 30-40% reduction in peak deviator stress, elastic modulus, and internal friction angle. Subsequent cycles lead to progressively slower degradation, the degradation rate decreased and approached stabilization within the investigated range of 30 cycles. Although increasing confining pressure enhances mechanical behaviour by promoting soil densification, this benefit diminishes as the number of freeze-thaw cycles increases. Based on experimental data, a damage model incorporating the elastic deformation phase was developed. By linking Weibull distribution parameters to test variables, a coupled freeze-thaw and loading damage variable was formulated. Model validation shows close agreement between predicted and experimental results, accurately capturing the effect of freeze-thaw cycles on strength degradation and damage evolution during loading. These findings provide a reliable theoretical basis for the safety design of engineering structures in cold regions.

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.

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.