Real-time experiment investigations on the coupled thermomechanical and cracking behaviors in granite containing three pre-existing fissures

Abstract

This paper investigates the coupled thermomechanical (TM) behavior, in real time, of granite containing three pre-existing fissures under uniaxial compression. The ligament angle spans from 75° to 120° with an interval of 15°, and the testing temperature varies from 25 °C to 700 °C. The strength and deformation of the granite are first considered as functions of the temperature and the ligament angle. The elastic modulus of the granite greatly decreases at 400 °C, and uniaxial compression strength of the granite substantially decreases at 600 °C. The fracturing behavior of the granite specimens depends on not only the temperature but also the fissure array. For relatively small ligament angles, the crack coalescence pattern only depends on the ligament angle, while for relatively large ligament angles, the crack coalescence pattern depends on both the ligament angle and the temperature. The granite specimens mainly exhibit tensile failure modes at 25–300 °C, the brittle-ductile transition occurs at 300 °C, the granite specimens experience a mixed tensile-shear failure mode at 300–400 °C, and they experience a shear failure mode at T = 400–700 °C. Moreover, the thermal damage of the granite is analyzed by thin section observation and electron microscopy scanning (SEM). Thermally induced micro-cracks in the granite mainly include intercrystalline cracks and intracrystalline cracks, which occur dramatically at T = 400–700 °C. Electron probe micro analyzer (EPMA) experimental results show that the physical properties of the granite are considerably affected by temperature, while the chemical composition of the minerals remains unchanged at T = 25–700 °C. The damage to the microstructure of the granite at high temperatures is caused by physical changes rather than chemical changes.