To study the influence of high-temperature-impact dual-cycle cumulative damage on the dynamic mechanical characteristics of granite, specimens with a height-to-diameter ratio of 0.8 were subjected to high-temperature cycling treatments at 100, 300, and 500 ℃ for 2, 4, and 6 cycles, respectively. The P-wave velocities before and after treatments were measured. Constant-amplitude cyclic impact tests under gas pressures of 0.25, 0.30, and 0.35 MPa were conducted using a split Hopkinson pressure bar (SHPB) system. The effects of temperature, high-temperature cycles, impact gas pressure, and impact cycles on the dynamic behavior of granite were systematically investigated. Based on Lemaitre’s continuum damage constitutive model and the strain equivalence principle, cumulative damage factors for high-temperature and impact cycles were defined, and the critical dual-cycle cumulative damage factor was analyzed. Results indicate that with increasing initial high-temperature cumulative damage and impact gas pressure, the crack morphology of granite during the first impact evolved from single cracks to complex crack networks with increased connectivity, while peak stress decreased and peak strain increased. Significant variations in peak stress and strain were observed between the first and final impacts during cyclic loading. The influence of factors on the cumulative impact damage under high-temperature cycling followed the order: impact gas pressure>temperature>number of high-temperature cycles. The critical high-temperature-impact cumulative damage factor was determined to range between 0.625 and 0.676. These findings provide theoretical support for safety assessment in deep underground resource extraction.

In order to study the effect of high temperature-water cooling on the physical and mechanical properties of basalt, physical test, static uniaxial compression test, X-ray diffraction and electron microscope scanning test were carried out on basalt samples after water cooling at room temperature (25 ℃) and high temperature (100 ℃, 300 ℃, 450 ℃and 600 ℃). The micro damage mechanism of samples after high temperature-water cooling and the correlation between physical and mechanical properties of samples and temperature were analyzed. The results show that high temperature-water cooling does not change the main mineral components of basalt, but has an effect on its relative content; The larger the temperature gradient is, the more internal cracks are caused by thermal shock. When the temperature rises to 600 ℃, the dimple fracture appears in the microstructure. When the temperature is increase, the samples show the change from gray green to red, the enhancing of mass loss rate, the weakening of longitudinal wave velocity, the slowing down of stress-strain curve, the deterioration trend of peak strength and elastic modulus, and the deterioration degree gradually intensifies; Under the coupling action of high temperature water cooling and load, the evolution curve of the total damage variable of the specimen gradually slows down with the increase of temperature, indicating that the specimen gradually changes from brittle to plastic.

To study the dynamic mechanical behavior of concrete under three-dimensional coupled static-dynamic loading, split Hopkinson pressure bar (SHPB) experiments were carried out under combined axial compression, confining pressure, and impact loading. A stress initialization method was introduced into the LS-DYNA program, and a sequential analysis approach consisting of implicit static loading followed by explicit transient dynamic loading was used to simulate the coupled static-dynamic loading process. The influence of different static load combinations on the strength and failure characteristics of concrete was systematically analyzed. The results show that, at the same impact velocity, the dynamic compressive strength of concrete increases with increasing confining pressure, which provides a protective effect on the specimen. A critical axial compression value is observed: below this threshold, axial compression enhances specimen strength, whereas beyond it, axial compression leads to strength deterioration. The introduction of the stress initialization method enables accurate realization of constant pre-stress conditions before dynamic analysis. Comparative analysis between experimental and numerical results shows that static loading provides limited compaction enhancement, while changes in static load combination significantly alter the internal stress distribution, which is the main factor affecting the dynamic strength of concrete. Numerical simulations effectively capture the failure process of concrete under three-dimensional coupled static-dynamic loading, revealing that the dominant failure mode is compressive-shear failure. Furthermore, the damage evolution of concrete can be reliably predicted by analyzing the time-history curves of damage variables in the numerical model.