Study On Calculation Methods Of Stress Intensity Factor For Cracks In Typical Joints Of Ship Hull

Semi-elliptical surface cracks always occur in the welded structures such as ships,and the stress intensity factor analysis for such cracks is of major importance in damage tolerance design.The weight function method is useful to determine stress intensity factors under complex stress field.In this paper,practical formula of general point load weight function for surface crack is developed based on the expression initially proposed by Wang et al.In order to overcome the limitation of applicable range on crack shape,three-dimensional finite element analyses have been performed to calculate the stress intensity factors for surface cracks with aspect ratio a/c=0.05~1.0 and crack depth-to-thickness ratio a/T = 0.01~0.8.The unknown parameters in general form can be determined from reference stress intensity factor solutions.The derived weight functions are then validated against available stress intensity factors at surface and deepest points under several two-dimensional stress distributions up to sixth order,and the differences between weight function and FEM are mainly less than 10%,showing a fairly good accuracy.The proposed weight function may also provide an efficient approach to evaluate the surface fatigue crack growth in welded structures subjected to complicated stress fields due to stress concentration and welding.In addition,the proposed weight function is applied to calculate the stress intensity factors for typical welded joints in ship structures.The results show that the proposed weight function may also provide an efficient approach to evaluate the surface fatigue crack growth subjected to complicated stress fields such as residual stresses due to welding and post-weld improvement.