Gang Wang

To investigate the influence mechanism of high‐temperature water‐cooling on the dynamic mechanical behavior of granite, a combined approach of impact loading experiments and discrete element simulations was employed. The study systematically analyzed the dynamic fracture behavior and thermo‐mechanical damage mechanisms of granite after high‐temperature water‐cooling treatment. The results indicate that heat‐treatment temperature and impact velocity exert a synergistic influence on the dynamic response of granite. A critical temperature of approximately 450°C was identified for dynamic peak stress: below this threshold, the stress variation remains moderate, while above it, a sharp decrease occurs. Increasing impact velocity significantly enhances the strain‐rate effect; however, this effect is weakened under high‐temperature conditions. An inflection point in the proportion of dissipated energy appears near 600°C, and the failure mode transitions from blocky splitting at low temperatures to pulverized fragmentation at high temperatures. A thermo‐mechanically coupled grain‐based model (GBM) was developed to reproduce the experimental observations, revealing that the rapid increase in transgranular cracks beyond 450°C leads to a sharp reduction in crack initiation stress. By distinguishing the respective contributions of intergranular and transgranular cracking, a thermo‐mechanical damage evolution model was established. The analysis shows that intergranular cracks dominate in the low‐temperature stage, whereas transgranular cracks become predominant at higher temperatures, resulting in intensified damage. This study provides a theoretical foundation for the safety assessment of deep geothermal energy exploitation.

This study aimed to enhance the slurry performance and durability of coal gangue-based geopolymers (CGGP) by incorporating four types of nanomaterials: nano-SiO₂ (NS), graphene oxide (GO) nanosheets, nano-CaCo₃ (NC), and nano-Al₂O₃ (NA). The microstructure and underlying mechanisms were thoroughly investigated using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The results indicate that the type and dosage of nanomaterials significantly influence the rheological properties, strength development, setting time, porosity, and water absorption of CGGP. Specifically, the addition of GO nanosheets drastically reduced fluidity, with a 73.33% decrease in flowability compared to the control group at a 2.0 wt.% dosage. Nano-SiO₂ exhibited the most pronounced effect in improving compressive strength and shortening the setting time, with the optimal accelerating effect observed at a 1.5 wt.% dosage. Nano-CaCO₃ primarily acts as a filler. Though its reactivity is relatively low, at an appropriate dosage (1.5 wt.%), it can effectively reduce porosity and water absorption. Moreover, at a dosage of 1 wt.%, it exhibits the optimal 28-day compressive strength, which is 54.18% higher than that of the blank group. Nano-Al₂O₃ demonstrated a relatively stable accelerating effect on setting and yielded the best pore structure and strength at a 1.5 wt.% dosage. SEM analysis revealed that the incorporation of an appropriate amount of NC particles significantly improved the microstructural densification of the polymer. Concurrently, EDS results confirmed the positive influence of the nano-Al₂O₃ material on the distribution of hydration products and the interfacial structure. This research provides an important theoretical basis and technical support for the high-performance design and widespread engineering application of coal gangue-based geopolymers.

Dynamic mechanical characteristics of water-saturated frozen granite under cyclic impact loading were investigated at 10, 0, −10 and −20°C using a split Hopkinson pressure bar (SHPB) apparatus. Key parameters including dynamic strength, strain evolution, fracture morphology and energy dissipation were quantitatively analysed under repeated loading conditions. The results indicate that progressive reduction in dynamic strength with increasing impact cycles was observed. Crack development exhibited a transition from initiation to axial penetration, with more severe fracture and wider cracks detected at lower temperatures. Penetration cracks and complete splitting occurred notably at −10 and −20°C, corresponding to enhanced brittleness and reduced dynamic load-bearing capacity. A cumulative damage constitutive model was formulated based on Lemaitre's equivalent strain principle and statistical damage theory. The model captured the temperature-dependent degradation of dynamic stress–strain response, providing accurate representation of damage evolution during cyclic impact at sub-zero conditions.