Analysis and prediction of thermal shock in brittle materials

The indentation quench method has been studied through both experiments and modeling. Practical results are obtained for alumina, whisker reinforced alumina, cermet and high speed steel. The crack growth vs temperature difference curves show no crack growth at very low Delta Ts, stable crack growth at medium Delta Ts and unstable crack growth above a certain Delta T (Delta T-U) and these regimes are explained in the analysis. The stable and unstable crack growth are governed by the combination of residual and thermal stress. An expression has been derived for the prediction of thermal shock resistance and it is shown that the fracture toughness is of great importance. The presence of residual stress results in the greater sensitivity of the indentation-quench method compared to other approaches, and also makes it possible to define specific values of Delta T adapted to specific applications. The method can be used to explore susceptibility to thermal fracture in a range of brittle materials on condition that it is possible to insert an indentation precrack. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. AN rights reserved.