Numerical study of strength mismatch in cross-weld tensile testing

The strength mismatch effect on the deformation behaviour of defect-free cross-weld tensile specimens, where there is a variation in strength along the length of the specimen, was investigated through 2D finite element analysis. A simple bi-material model, which is generally used in current engineering assessments (e.g. R6 “Assessment of the integrity of structures containing defects”) to examine the strength mismatch effect on the deformation and fracture behaviour of a weld which actually includes a heat-affected-zone, could lead to nonconservative or overly conservative predictions. In fusion welded components, one would generally observe that there is a heat-affected zone where the material properties are different from the weld and base material, and there is a continuous gradient of properties between the two. The material properties in HAZ are generally assigned discretely; however, in our multi-material model these properties are successfully assigned continuously by embedding subroutines into finite element model. This multi-material approach was used to examine the effect of strength mismatch on the local and global deformation behavior of fusion welds. It has been found that the bi-material modeling, by ignoring the HAZ, and multi-material discrete HAZ modeling of the cross-weld specimens leads to unrealistically biaxial stresses at the interfaces where there is an abrupt variation of the material properties. However, multimaterial continuous HAZ modeling eliminates unrealistic stress biaxiality and enables to examine the local deformation more accurately. It was also found that the global stress-strain behaviour obtained using the bimaterial and multi-material modeling is different.