Abstract:
In order to study the influence of cumulative damage from high-temperature and impact double cycles on the dynamic mechanical properties of granite, granite specimens with a height-to-diameter ratio of 0.8 were used as the research objects. The longitudinal wave velocities before and after 2, 4, and 6 cycles at 100 ℃, 300 ℃, and 500 ℃ were measured. Equal-amplitude cyclic impact experiments with impact pressures of 0.25 MPa, 0.30 MPa, and 0.35 MPa were conducted using the SHPB test device to investigate the effects of temperature, the number of high-temperature cycles, impact pressure, and the number of impact cycles on the dynamic characteristics of the granite specimens. Meanwhile, based on the Lemaitre continuous damage constitutive model and the strain equivalence principle, the cumulative damage factors of cyclic high-temperature and cyclic impact were defined to analyze the critical cumulative damage factor of high-temperature and impact double cycles. The results show that as the initial high-temperature cumulative damage and impact pressure increase, the crack morphology of the granite specimens during the first impact evolves from a single crack to a complex crack, the penetration degree increases, and the peak stress decreases successively. The peak stress of the first impact and the last impact in the cyclic impact of the granite specimens changes significantly. The influence on the cumulative dynamic impact damage of the granite specimens after cyclic high-temperature treatment in the order of impact pressure > temperature > the number of high-temperature cycles was obtained. The critical high-temperature and impact cumulative damage factor is between 0.625 and 0.676, which can provide theoretical support for the safety assessment of underground mining of deep resources.
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