Constitutive model coupled with mechanical effect of volume change and transformation induced plasticity during solid phase transformation for TA15 alloy welding

In this paper, the elastic-plastic constitutive model for TA15 titanium alloy welding which describes the mechanical effect of volume change during diffusional solid phase transformation and transformation induced plasticity (Trp) during diffusionless solid phase transformation has been established. The model in combination of mixed strain hardening and mechanical effect of solid phase transformation is coupled in MSC. Marc software by secondary development and applied for finite element numerical simulation of the welding process. Firstly, the simulation results with and without consideration of Trp strain are compared. It is indicated that Trp strain can moderate the stress distribution, make the high tensile stress and high compressive stress converge to zero and finally lower the residual equivalent stress. Meanwhile, the simulation results with consideration of volume expansion and volume shrinkage are compared. Volume expansion produced in the cooling stage can offset the volume shrinkage due to temperature dropping that lower the residual equivalent stress. Volume expansion accompanied by phase transformation which proceeds at low temperature is better than that at high temperature, while volume shrinkage at high temperature is better than that at low temperature at lowering the residual equivalent stress. The influences of Trp strain and volume change strain are reasonable both in spatial distribution and histrionic evolution. Using the established constitutive model, welding residual stress and strain are in good agreement with the theoretical results.