Virtual field method for identifying elastic-plastic constitutive parameters of aluminum alloy laser welding considering kinematic hardening

The local high temperature of laser welding affects the mechanical properties of aluminum alloys. In this paper, a three-dimensional digital image correlation system was used to measure the displacement field of the aluminum alloy-laser welding joint under a uniaxial tensile load. By taking into consideration the metal properties of welded joints, an estimation correction scheme for updating stress was designed for anisotropic materials based on the kinematic hardening process, and the proposed method was then applied to the nonlinear virtual field method, the validity of which was verified by a finite element simulation. The elastic-plastic constitutive parameters of various local regions of the welding joint (fusion zone, heat-affected zone, transition base zone, and base zone) were then retrieved from the measured field data, and the stress-strain relationship of each sub-region was established. The results show that the mechanical properties of the laser-welded joint are weakened while the Poisson's ratio decreases with the increase of the weld distance. Furthermore, the elastic modulus of the heat-affected zone is evidently lower than that of the other sub-regions, while it also has the lowest yield strength and the highest plastic strain rate. All these results are consistent with the trend of the hardness measurements.