A comparative study on the dynamic loading response of heat-treated soft and medium hard rocks

Abstract

The present study assesses the effects of thermal exposure on the strength, stiffness, and fracture propagation in different rocks subjected to impact loading. The dynamic loading response of soft (synthetic die stone) and medium hard (natural marble) rocks are compared in this study. In the experiments, Split Hopkinson Pressure Bar (SHPB) tests are carried out on the heat-treated rock samples. A high-speed camera records the whole failure process of these specimens, and digital image correlation (DIC) is employed to track the evolution of strain during SHPB compression testing. The variation of mechanical properties of intact rocks with heating temperature is characterized by various thermal zones depending on the transition temperature, which identifies a significant shift in the impact loading response due to heating-induced micro-crack formation. Rocks made of synthetic materials and marble have transition temperatures between 100 and 150 °C and 500 – 650 °C, respectively. In the pre-transition regime, the dynamic compressive strength slightly rises or stays almost unchanged, whereas in the transitional regime, compressive strength falls drastically, and it does not show any vital changes with increasing treatment temperatures in the post-transitional regime. For synthetic rocks and marble, the critical heating durations are 10 and 5 h, respectively, and strength changes are relatively minimal after these heating durations. With increasing temperature (from 30 °C to 300 °C), the fracture pattern of synthetic specimens shifts from shear-tensile-dominated to tensile-dominated followed by shear-dominated. For marble specimens, the fracture pattern shifts from shear-tensile-dominated to shear-dominated as the temperature rises from room temperature to 650 °C.