A Proposal for evaluation method of crack growth due to cyclic overload for piping materials based on an elastic-plastic fracture mechanics parameter

Yamaguchi, Yoshihito ; Li, Y.* ; Sugino, Hideharu*; Katsuyama, Jinya  ; Onizawa, Kunio 

Niigata-ken Chuetsu-Oki earthquake occurred, whose magnitude was beyond the assumed one provided in seismic design. Therefore it becomes an important issue to evaluate the crack growth behaviors due to the cyclic overload like large earthquake. Fatigue crack growth is usually evaluated by Paris's law using the range of stress intensity factor (K). However, K is inappropriate in a loading condition beyond small scale yielding. In this study, the crack growth behaviors for piping materials were investigated based on an elastic-plastic fracture mechanics parameter, J-integral. It was indicated that the crack growth due to the cyclic overload beyond small scale yielding could be the sum of fatigue and ductile crack growth. The retardation effect on the crack growth was observed after excessive loading. The modified Wheeler model using J-integral has been proposed for the prediction of retardation effect. Finally, an evaluation method for crack growth behaviors due to the cyclic overload was suggested.