抄録
In recent years, Japanese nuclear power plants experienced multiple large earthquakes. It is very important to assess the seismic safety of piping taken the occurrence of such a large earthquake into account, when a crack exists in pipe welding joint. One of the key issues is the effect of excessive loading in the seismic response wave on the fatigue crack growth behaviour. We performed fatigue crack growth tests under constant amplitude cyclic loading with a single excessive tensile/compressive load for Ni-based alloy weld metal. Acceleration and retardation was confirmed in crack growth due to the excessive loading. The stress distribution in front of crack tip and the shape of crack tip were investigated to clarify the cause of changes of crack growth rate. A crack growth evaluation method has been proposed considering the effects of the excessive loading based on the variation of the stress distribution in front of crack tip and the crack blunting. The predicted crack growth rate by the proposed method was in good agreement with the experimental ones.
