Abstract
Micro-crack growth behaviors in ratcheting fatigue tests were investigasted to discuss the fatigue life reduction mechanism in ratcheting conditions. Ratcheting fatigue tests for 316FR stainless steel were conducted at 550C in order to discuss the design criteria for the commercialized fast reactor system. Fatigue lives decrease with increasing the accumulated strain, but the life reduction was negligible when the accumulated strain was less than 2.2%. Micro-crack growth behavior can be devided into initiation and growth stage. The crack initiation length was approximately 0.2mm. The initiation life was almost negligible when the fatigue life decreased by ratcheting. The micro-crack initiation life shortening was considered as the mechanism of fatigue life reduction in ratcheting conditions.
