A CONSIDERATION OF EVALUATION OF FATIGUE-CRACK PROPAGATION RATE FROM EFFECTIVE STRESS INTENSITY FACTOR RANGE

The fatigue crack propagation law was investigated for the two cases of crack propagation in a region of welding residual stress and after overloading. In the former case, the crack propagation rate da/dN was found to depend on the stress ratio R defined by sigma(min)/sigma(max) where sigma(min), sigma(max) , are the minimum and maximum cyclic stresses. Due to the tensile residual stress, the crack propagation rate increased as the stress ratio decreased in the range -2 less than or equal to R less than or equal to 0. In the latter case, the crack propagation rate da/dN after overloading was higher than that for the constant stress amplitude test at first and then became lower. The crack propagation rate was thus affected by both the residual stress and the overloading. However, the crack propagation behavior correlated well with the crack closure behavior. Therefore, in the cases considered here, the crack propagation law can be reasonably evaluated from the effective stress intensity factor range Delta K-eff.