Effect of Small Inner Cracks on Macrocrack Propagation

In this chapter, time-dependent and cycle-dependent crack propagation tests were conducted using notched specimens of SUS304 stainless steel in 4 major cases to investigate the effect of small inner cracks introduced by high-temperature cp-typeCp-type creep-fatigue on macrocrackMacro crack propagation. For the case of a macrocrack propagation in the zone containing no small crackSmall crack (Case 1), the macrocrack propagation under cc-typeCc-type and cp-typeCp-type conditions is time-dependent, while the macrocrack propagation under pp-typePp-type and pc-typePc-type conditions is cycle-dependent. For the case of a macrocrack propagation in the zone containing uniformly distributed pre-small cracks (Case 2), the existing small inner cracks accelerate both time-dependent and cycle-dependent macrocrack propagation. For the case of a macrocrack propagation in the process zone with small crackSmall crack nucleation (Case 3), many small intergranular cracks were observed near the main crack inside the specimen, and the macrocrack propagation rateCrack propagation rate was approximately 4 times higher than that of the time-dependent crack propagation of case 1. For the case of a macrocrack propagation combined with Case 2 and Case 3 (Case 4), the macrocrackMacro crack propagation rate is almost equal to that in Case 3 under same conditions.