Analysis of Energy Properties and Failure Modes of Heat-Treated Granite in Dynamic Splitting Test

Abstract

Dynamic Brazilian disc (or splitting) tests were carried out to study the characteristics of energy dissipation and failure behavior of heat-treated granite under impact loading. Six groups of granite samples were treated at the temperatures of 25°C, 100°C, 300°C, 500°C, 700°C, and 900°C, respectively. Each group of heat-treated samples was tested with three impact velocities of 5.4, 7.7 and 13.7 m/s in a modified split Hopkinson pressure bar. An average change rate of incident energy (ACRIE) was proposed to characterize the loading rate effect. The effects of treatment temperature and ACRIE on the energy dissipation and the failure patterns of samples under impact loading were investigated. The results show that the energy dissipation of the granite decreases with the increase of treatment temperature but increases with the increase of the ACRIE. A rise in treatment temperature or ACRIE may lead to smaller size and greater number of sample fragments. The effect of treatment temperature becomes more obvious as the ACRIE increases. The energy utilization ratio of the granite is generally less than 30 % and has an opposite effect when compared to the loading rate. In addition, the dynamic tensile strength of the samples increases almost linearly with the transmitted wave energy. These studies also indicate that the resistance of rock against tensile failure can be well characterized from the perspective of energy dissipation. Nomenclature c 0 = ultrasonic P-wave velocity of sample before heating c 1 = ultrasonic P-wave velocity of sample after heating D = thermal damage of sample V 0 = impact velocity of projectile W i = energy of incident stress wavė W i = average change rate of incident energyManuscript

Study on the dynamic characteristics of rock surrounding a wellbore in energy storage areas during deep geothermal energy mining

“…Considering that the rock surrounding wellbores was affected by drilling vibration, thermal impact and earthquake waves and that tensile failure frequently occurred in the wellbore, dynamic Brazilian disc splitting tests were carried out. The cumulative damage of the rock increased exponentially with increasing strain rate, the ultimate failure modes of the disc rock samples were closely related to the impact velocity, and the dynamic tensile strengths measured by the test were far larger than the static tensile strengths [ 21 – 24 ]. Analysing the above studies, it was found that high temperature, high in situ stress and dynamic disturbances were taken into account, but the influence of the cross section of high-depth wellbores, medium water and cycle heat recovery times was overlooked.…”