Effects of Damage on Thermal Shock Strength Behavior of Ceramics

Abstract

When subjected to severe thermal shock, ceramics suffer strength degradation due to the damage caused by the shock. A fracture‐damage analysis is presented to study the effects of damage on the thermal shock behavior of ceramics. It is assumed that a narrow strip damage zone is developed at the tip of a preexisting crack after a critical thermal shock and the damage behavior can be described by a linear strain‐softening constitutive relation. Damage growth and strength degradation are determined based on fracture and damage mechanics. Numerical calculations are carried out for two ceramic materials, and the strength degradation agrees quite well with experimental results. The effects of bridging/damage stress, the fracture energy of the bridging/damage zone, and specimen size on thermal shock strength behavior are studied. A higher fracture energy can enhance the residual strength of thermally shocked ceramics and, for a given fracture energy, a higher bridging stress is needed to reduce the strength degradation. It is also shown that the thermal shock strength behavior is size‐dependent, and a high value of (KIC/Ob)2, where KIC is the intrinsic fracture toughness and Ob is the bending strength, can improve significantly the residual strength.