Abstract: At present, the errors between welding residual stress simulation results and experimental measurements are large for high strength low alloy steel when adopting coupled temperature-displacement analysis and omitting solid-state phase transformation effect. Based on the multi-physical coupling relationships, a multi-physical coupling constitute equation is established by using heat transfer, solid-state phase transformation theory and continuum mechanics to improve welding numerical simulation accuracy and then the equation is implemented into the general purpose implicit finite element program via user material subroutine. The evolution of stress and strain components of free dilation test, transformation induced plasticity test and flat plate welding test are investigated by means of both numerical simulations and experiments. The results suggest that transformation strain caused by volume change has significant effect on welding residual stress, which not only changes the magnitude of residual stress and even changes the sign of residual stress. Transformation induced plasticity strain lowers the magnitude of residual stress. The extent of welding residual stress change has a close relationship with the degree of phase transformation, fully-transformed region is larger than partially-transformed region, and partially-transformed region is larger than untransformed region. The final transformation strain is approximate to transformation induced plasticity strain. The presented research method provides a theoretical basis for deeper understanding of welding process and optimization of welding technology.

Key words: multi-physical coupling constitute equation, fully implicit integration algorithm, numerical simulation, residual stress, strain component