J-Q-M Approach for Failure Assessment of Fusion Line Cracks: Two-Material and Three-Material Models

The theoretical background for the J-Q-M approach for quantifying the constraint in weldments for fusion line cracks is presented. In this model, Q quantifies the geometry effects and M the material mismatch effects. Initially the approach was developed for a two-material modified boundary level (MBL) model, but later was extended to include three materials: weld metal, heat-affected zone and base material, and more realistic specimen geometries. The analysis with MBL models showed that the effect of mismatch was rather independent of the T-stress for both bi- and tri-material models, indicating that Q and M could be treated independently. However, analysis of fracture mechanics tension specimens made of three materials revealed that the mismatch effect in some cases could depend on the geometry effects. New calculations have demonstrated that the dependence/independence is related to load level, ratio of mismatch, and the local geometry.