Elastic Energy at Fracture and Surface Energy as Design Criteria for Thermal Shock

TLDR

Crack propagation in thermally shocked specimens is driven by elastic energy stored at fracture and opposed by effective surface energy dissipated to create new surfaces. The authors propose thermal‑shock damage‑resistance parameters that enable relative comparison of the expected degree of damage in different materials. An analytical expression for the mean crack area in a spherical body is derived and applied in three numerical examples to predict fracture behavior of materials with diverse properties. The model agrees well with experiment and shows that high Young’s modulus, Poisson’s ratio, and effective surface energy, combined with low strength, predict low damage, informing material selection for severe thermal shock.

Abstract

The physical properties which affect the propagation of cracks in specimens fractured by thermal shock are discussed. The driving force for crack propagation is provided by the elastic energy stored at fracture. The mechanism of energy dissipation which will tend to arrest the propagating cracks is provided by the “effective surface energy” required to produce the newly formed crack surfaces. An expression is derived applicable to a body of spherical shape for the mean area traversed by cracks nucleated by thermal shock. Three numerical examples are given for materials with widely different physical properties, and their fracture behavior is predicted. Good agreement with experiment was obtained. Thermal shock damage resistance parameters suitable for the relative comparison of the “degree of damage” to be expected in materials fractured by thermal shock are proposed. The criteria for a low degree of damage are high values of Young's modulus of elasticity, Poisson's ratio, and effective surface energy and low values of strength. Recommendations are made for the selection of materials for severe thermal shock, where the best materials available are known to fail.