Modelling the Effect of Residual Stresses on Damage Accumulation Using a Coupled Crystal Plasticity Phase Field Fracture Approach

Residual stresses are a crucial factor in assessing the integrity of welded joints. These stresses are known to influence the joint’s strength under additional loading, with the altered grain structure at and near the joint a complicating factor. Consequently, a mesoscale model is essential to understand the accumulation of damage in components subjected to external loading, as well as the impact of prior loads on failure. This study addresses the interplay between loading direction and grain morphology, explicitly investigating damage accumulation. The mesoscale model includes a coupled crystal plasticity and a phase field fracture model to estimate the deformation induced during a laser beam weld of 316H stainless steel. The displacement boundary condition was derived from a mechanical model of the weld, with the application of a Chaboche model. The temperature field required for the grain growth and mechanical models were obtained through a thermal fluid dynamics framework. Investigation of crack initiation and propagation was carried using a phase-field fracture model, which allowed the consideration of prior loading. This study indicated that the direction of loading plays an important role in damage susceptibility. The modified grain structure based on the welding simulation showed a different strain at failure compared to the 316H stainless steel parent material. The achieved strain at failure was found to be lower in normal loading compared to the transverse direction. Presently, the crystal plasticity model fails to estimate the macroscopic residual stresses, illustrated by damage propagation resulting in earlier than expected ductile failure upon reloading. The potential causes are addressed and discussed in detail.