In-plane shear (Mode Ⅱ) crack sub-critical propagation of rock at high temperature

摘要

In-plane shear crack sub-critical propagation of rock at high temperature was studied by finite element method and shear-box (I.e. Compression-shear) test with newly designed electrically conductive adhesive method. Numerical and experimental results show that the normalized shear (Mode Ⅱ) stress intensity factors, KTⅡ/KⅡ0 is decreased as the temperature increases because high temperature can improve stress distribution at crack tip and reduce the Mode Ⅱ stress intensity factor. Microscopic features of fractured surface are of little pits and secondary micro-cracks in the vicinity (1.5-4.0 mm) of the crack tip. The chevron-shape secondary cracks gradually merge in the length of about 4-5 mm and disappear along the direction of crack propagation. Stable shear crack propagation time is increased with the increasing temperature while the stable shear crack propagation rate is decreased with the increasing temperature, since high temperature can increase the shear (Mode Ⅱ) fracture toughness and prevent the crack growth. It is necessary to ensure the ligament of specimen long enough to measure the maximum unstable crack propagation rate of rock.