Crack Initiation and Propagation in Thermal Shock Fatigue of Stainless Steel

Fatigue crack growth tests were preformed on austenitic stainless steel subjected to repeated thermal shocks using a specially designed test system for thermal shock fatigue, in which liquid air is sprayed onto the center of a disk-shaped specimen heated to about 200°C. The fatigue crack growth was found to occur while producing the striation on the fracture surface each time a thermal shock is applied. The crack growth characteristics in thermal shock fatigue can be well explained by the results of analysis of thermal stress intensity factor (SIF). The crack propagation rate da/dN achieves its maximum at the same crack length as in the curve giving the relationship between SIF and the crack length. The results of the observation have also been described on the initiation and propagation of small fatigue cracks at the notch root.