Investigation on Evaluation Method Based on J Integral for Retardation of Crack Growth Due to Excessive Loading Beyond Small Scale Yielding Condition

Niigata-ken Chuetsu-Oki earthquake occurred in July 2007, whose magnitude was beyond the assumed one provided in seismic design. Therefore it becomes an important issue to evaluate the effect of excessive loading, in particular, for the components with existing crack. Fatigue crack growth rate is usually expressed by Paris’s law using the range of stress intensity factor (ΔK). However, applicability of the model to loading conditions beyond the small scale yielding remains as an issue since ΔK is inappropriate in such a high loading level. In this study, the fatigue crack growth behaviors after applying the excessive loads were investigated using austenitic stainless steel and carbon steel. Instead of ΔK, J-integral value for crack growth evaluation due to cyclic loading has been applied based on the experimental data to treat the excessive loading beyond small scale yielding. The finite element method (FEM) analyses were conducted to evaluate the stress distribution and plastic zone size for the excessive loading condition. The modified Wheeler model using J-integral range, ΔJ, has been proposed for the prediction of retardation effect on crack growth after excessive loading. It was indicated that retardation effect by excessive loading beyond small-scale yielding could be quantitatively evaluated using the J-Wheeler model.