Interaction of surface cracks subjected to non-uniform distributions of stress

Closely-spaced surface cracks in structures interact with each other when subjected to load. The degree of interaction depends strongly on the distribution of stress that is applied. In pressure boundary components, thermal shock, residual stress and global bending can all cause load distributions that are non-uniform through the wall thickness. A wide range of crack pairs subject to various non-uniform stress distributions have been modelled using finite element analysis. Cracks sometimes interact more strongly under non-uniform loading than when loaded in uniform tension. Consequently, interaction criteria developed by considering uniform tension may not be inherently conservative for all loading conditions. A simple weight function method for determining the interaction of twin cracks under an arbitrary through-wall stress is presented, and weight function coefficients for a wide range of crack sizes and aspect ratios are given.