CONTACT DAMAGE SUBMITTED TO THERMAL-SHOCK - A METHOD TO EVALUATE AND SIMULATE THERMAL-SHOCK RESISTANCE OF BRITTLE MATERIALS

A criterion for study of the thermal shock resistance of brittle materials is derived. It makes use of the stable extension stage of Vickers indentation cracks under the action of the thermal transient stress which appears during quenching. During this stage, the relative increase in crack length can be measured. If plotted as a function of indentation load, it can be used as an indicator of thermal shock resistance. On the basis of these well defined conditions, it is possible to reflect the empirical ranking of various materials (float glass, glass-ceramics and polycrystalline alpha-SiC). Furthermore, the anisotropy of the thermal transient stresses, as deduced from the shape of the quenched part, can be revealed. Finally a critical point, separating stable and unstable crack extension, is defined. It may thus become possible to evaluate quantitatively the maximum value of thermal transient stress, without knowledge of the heat transfer process during quenching.