173 / 2024-03-11 09:05:13

Deformation and fracture mechanisms of limestone under coupling effects of real-time temperature and strain rate

Deep coal mining,Real-time temperature,Dynamic properties,Microscale fracture

The deep surrounding rock medium is often subjected to the coupling effect of real-time high temperature and high strain rate, and studying its deformation and fracture mechanism are of great significance for the safe and efficient mining of deep coal resource. In this study, a split Hopkinson pressure bar (SHPB) test system with real-time temperature control was developed, and dynamic tests on limestone taken from deep coal mine within real-time temperatures of 25 to 800 ℃ were carried out. Additionally, the scanning electron microscope (SEM), X-ray diffraction (XRD) and energy dispersion spectrum (EDS) tests were conducted to analyze the fracture mechanism of limestone at real-time temperatures. The results reveal that the dynamic compressive strength of limestone linearly declines with increasing temperatures, due to not being affected by thermal shock damage, its strength degradation is not significant after cooling to room temperature; whereas the dynamic elastic modulus exhibits a negative exponential nonlinear decrease with the increase in temperatures; the average strain rate has a positive correlation with the dynamic compressive strength of limestone, while the dynamic elastic modulus exhibits variations in accordance with the Boltzmann function and its relationship with the strain rate. The combined influence of strain rate and temperature on the dynamic compressive strength of limestone can be accurately described by a binary quadratic function. The action mechanism of real-time temperature on the limestone can be categorized into physical reinforcement, physical degradation, and the co-effect of physical and chemical deterioration. Physical reinforcement can be attributed to the densification of micropores caused by the crystal micro-expansion. Physical degradation is highly correlated with the formation of microcracks induced by thermal stress and intergranular expansion. The decomposition of dolomite at high temperatures leads to chemical deterioration, which compromises the dynamic properties of limestone.