Experimental and numerical investigations of microwave-induced damage and fracture formation in rock

Abstract

Microwave technology is increasingly used in laboratory tests and field applications as an effective rock breaking technique. The underlying mechanism of rock fracturing induced by microwave energy, however, has not been well addressed. In this study, we employ experimental and numerical methods to investigate the global and local damage of rock in microwave radiation direction, including the fracture formation process. Our analysis focuses on three damage indicators under microwave irradiation, namely P-wave velocity attenuation, temperature distribution and fracture pattern. For a diabase sample, our experimental results indicate that the microwave power and irradiation time has a substantial influence on these three indicators. With increasing power level and irradiation time, we measured a lower P-wave velocity, higher temperature, and more fractures within the rock substrate. We observed that under the same energy, heating at higher power levels for shorter durations has a better weakening effect. Our numerical results show that thermal stress mismatch in the local high-temperature area is the main reason for crack initialization. Nucleation and propagation of microcracks depend on the thermal stress induced by global temperature increase, the geometry of the sample and existing fractures.