Abstract
Mixed-mode thermal stress intensity factors (SIFs) are investigated at various temperatures using the method of caustics. First, theoretical caustic patterns are obtained for various types of optical systems in addition to the mode II SIF KII and mode I SIF KI ratios. Next, the values of the SIF are experimentally investigated at various temperatures for glass plates with an inclined artificial notch or a natural crack, and the effect of the crack on the sign of the SIF is considered. Then, it is determined whether or not crack extension occurs. It is shown that a negative value of the SIF KI occurs at the notch tip under high-temperature conditions. In contrast, the sign of the SIF KI at the natural crack tip under high-temperature conditions is positive. At low temperatures, the signs of the SIFs at the notch and the natural crack tip are positive. Crack propagation is observed when the sign of KI is positive. The direction of crack propagation initiating from the natural crack at high temperatures is in accordance with the theory of maximum circumferential tensile stress (σθ)max. At low temperatures, the crack extends slightly, and thereafter, the direction of crack propagation abruptly changes because of the compressive stress in front of the notch and the natural crack tip.
