A thermomechanical‐phase‐field approach for modeling of residual stresses in fusion welding

Abstract

The welding process of metallic components, such as using gas tungsten arc welding (GTAW), is often accompanied by detrimental deformations and residual stresses, which affect the strength and functionality of these welded components. In this work, a phase-field model, usually used to track the state of the phase-change materials, is embedded in a thermo-elastoplastic finite element model in order to simulate the welding process and the residual stresses. The phase-field method (PFM) enables us to track the melting front of the metal, due to the welding heat source, and to split the analysis domain into soft and solid regions. In this way, temperature and phase-field-dependent material properties can properly be assigned to different regions in the domain. The phase-field evolution is governed by Allen-Cahn equation and relies on specification of the free energy density function as the main driving force for the phase change. Having a coupled thermomechanical process during the welding heating-cooling cycle, the onset of residual stresses is associated with plastic deformations and can be observed after cooling to the ambient temperature. The plasticity model considers J2 plasticity with isotropic hardening. The coupled nonlinear system of equations is solved in the open-source FE package, FEniCS, with time discretization based on the finite difference method.