EXPERIMENTAL AND ANALYTICAL STUDIES ON THE EFFECT OF EXCESSIVE LOADING ON FATIGUE CRACK PROPAGATION IN PIPING MATERIALS

The seismic regulatory guide was revised in September 2006 and the Niigata-ken Chuetsu-oki earthquake, whose magnitude was beyond the design base seismic motion, occurred in July 2007. Due to these events, attention is being drawn to the evaluation of the effects of large scale earthquakes for some piping systems in which SCC and/or fatigue cracks may potentially occur. Many papers have been already published about the retardation effect that excessive loading has on fatigue crack growth. The retardation effect is treated qualitatively in regard to the plastic strain generated by excessive loading. In this work, crack growth after excessive loading is evaluated for carbon steel and austenitic stainless steel. Some cyclic excessive loading patterns such as stepwise increases or decreases were applied to fatigue crack growth experiments. The FEM analyses were conducted to evaluate the plastic region size during these loading conditions. PFM analyses were performed to evaluate the extent to which the retardation of crack growth influences the probability of failure.