EVALUATION OF EXCESSIVE LOADING EFFECT ON FATIGUE CRACK GROWTH BEHAVIOR BASED ON CRACK BLUNTING AND STRESS DISTRIBUTION IN FRONT OF THE CRACK TIP

It is very important to establish an evaluation method of the structural integrity Of piping beyond the small scale yielding condition due to large earthquakes. One of the key issues is the effect of excessive loading on the fatigue crack growth behavior. We performed fatigue crack growth tests under constant amplitude cyclic loading with a single excessive tensile/compressive load. The stress distribution in front of crack tip and crack blunting were estimated by FEM analyses. After the crack tip was blunted by the excessive tensile loading, the effect of the excessive loading on crack growth rate varied depending on the magnitude of the subsequent compressive loading. When a compressive load is enough to close the crack, the crack growth rate became higher than that before the excessive tensile loading while increasing the tensile stress in front of crack tip. A crack growth prediction 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 correlated with the experimental ones.