Crack path instabilities in a quenched glass plate

A crack driven by steadily quenching a hot glass plate into a water bath exhibits fascinating path instabilities that depend on the severity of the temperature jump involved in the quenching process. An experimental and analytical investigation of these crack path instabilities is presented in this paper. First, real-time observations of the growth of the crack at different temperature jumps are presented. With increasing temperature jump, the crack path changes from a straight path to a periodic oscillatory path, then to a chaotic oscillatory path, to an unstable (dynamic) straight crack path, and finally to multiple crack paths. The experimental observations show that the crack growth is not a steady process even though the quenching occurs at a constant speed. The experimental observations provide crucial insight and the basis for the analysis of the problem. The problem is then examined analytically by solving the underlying thermoelastic problem, within the framework of linear elastic fracture mechanics. The results of the numerical simulations in conjunction with the experimental observations are used to show that (i) the T-stress criterion commonly used for evaluating crack path instability is inapplicable to this problem, (ii) the crack path stability can be determined by using the maximum tangential stress criterion for crack advance and examining the divergence of adjacent crack paths, (iii) the initiation of a structurally unstable crack can be determined, and (iv) the complete oscillatory crack path can be obtained through an incremental solution of the thermoelastic problem.