Prediction of Inner Cracking Behavior in Heat-Resistant Steel under Creep-Fatigue Condition by Means of Three-Dimensional Numerical Simulation

Abstract

Figure 1 shows the relationship between inelastic strain range and the number of cycles to failure for high-temperature fatigue of Type 304 austenitic stainless steel [1]. From the viewpoint of the location of small cracks, creep-fatigue fracture can be divided into two types. One is a “surface cracking type” indicated by O in Figure 1, in which small intergranular cracks are initiated only on the surface of the specimen, and their growth and coalescence bring about the final fracture. It is known that this type appears at intermediate temperatures with relatively high strain rates (or stresses). As the cracks are initiated only on the surface of the specimen in this type, creep-fatigue damage can be evaluated by surface observation of cracks. On the other hand, with increasing the temperature and/or decreasing the strain rate (or stress), the region of cracking, which was limited to the surface of the specimen, extends inward and, finally, small cracks appear almost uniformly throughout the specimen.