Applicability of applied stress estimation method based on the micro hardness of fatigue fracture surface of stainless steel without striations

In the failure analysis of fatigue fracture, the estimation of applied stress by examining the fatigue fracture surface is important in order to investigate the cause of failure. A fractographic method using striations has been established. Striations, however, can be observed only when a crack propagated at relatively high rate. In the case of failure after a long period of operation under low stress condition, striations are rarely observed. The estimation of applied stress is almost impossible in such a case. Therefore, an estimation method which can be applied in the low stress intensity region where striations are not observed is desirable. In this study, the applicability of micro hardness measured directly on the fatigue fracture surface as a parameter for the stress estimation was examined, The hardness of fatigue fracture surface was correlated with the stress intensity factor range. In addition, as an approach to service load, the relationship between the hardness of fatigue fracture surface and K value was investigated using repeated two-step stress.