Brittle fracture revisited for a butt weld under a residual stress field

The role of crack tip plasticity is explored for crack advance in a plate containing a full-penetration butt weld. The main loading is taken to be the residual stress field as a result of the welding process. Assessments are made using a strip-yield model and a range of residual stress fields, with an emphasis on a self-balancing field with vanishing membrane and bending loads. The residual stress field includes those suggested by the British Standard ‘Guide to methods for assessing the acceptability of flaws in metallic structures’ BS 7910 (2019). The degree to which an elastic stress analysis suffices to give an accurate estimate of the crack tip driving force is determined by making comparison to the more accurate strip-yield model. It is found that a self-balancing residual stress field is unable to drive crack growth across the full cross-section: a mean tensile component and/or bending component of stress is needed to achieve this. The level of mean stress and bending stress in the residual stress field is dictated by the degree of constraint imposed by the surrounding structure during weld shrinkage.