Fracture Mechanical Estimation for the Maximum Defect Size Rendered Harmless by Peening for High Tensile Steel Welded Joint Containing a Surface Defect at the Weld Toe

Abstract

The purpose of this study is to estimate the acceptable defect size α_max after needle peening (NP) and laser peening (LP) for a high tensile steel welded joint containing a surface defect on a weld toe. The magnitude of the relationship between the positive value of the stress intensity factor range ΔK_T and the threshold stress intensity factor range ΔK_th was compared to determine whether the semi-circular crack propagated or not. The value of ΔK_T was evaluated from the applied stress distribution and residual stress distribution using the finite element analysis method. The value of ΔK_th was evaluated considering a local stress ratio in addition to a crack size. The estimation results of α_max of post NP and LP treatment were both consistent with experimental results. The new estimation method could provide safer α_max than that of former method.