Thermal Shock 1
As explained in the properties module, thermal shock is damage as a result of cooling or heating a material rapidly. When a material changes temperature, the atomic packing changes and therefore the material expands or contracts. If there is a temperature gradient in a material, the differing degrees of expansion cause stresses. Brittle materials are susceptible to thermal shock, because when thermal stresses are introduced with the change in temperature, they cannot deform plastically and therefore flaws propagate by fast fracture under the stress. As a result, most ceramics and glasses have low thermal shock resistance, and will fracture if they are heated or cooled too rapidly.
Thermal stress is introduced with a change in temperature because solids expand and contract with changes in temperature. If the surface of a specimen is heated or cooled, the surface temperature of the specimen is changed due to conduction of heat. Ceramics and glasses generally have a low thermal conductivity, which means that when exposed to a change in temperature, the specimen is heated or cooled at the surface but not at the centre of the solid. The surface therefore expands or contracts, and is restrained by the centre, which is unchanged.