Refining Welding Modelling for Prediction of Distortion Incorporating Mechanical Effects of Annealing

Finite Element Analysis (FEA) has become one of the most important engineering tools regarding weld modelling. Within weld modelling techniques, sequentially coupled thermal-mechanical analysis is accepted as the most reliable FEA method for predicting welding induced distortion and stresses. This analysis can incorporate all the thermophysical properties and diverse weld modelling aspects such as: filler metal deposition, phase transformation or material relaxation at high temperatures. In this regard, material relaxation at high temperatures has been reported as a possible cause of the discrepancy between numerical simulations and experimental results.

This study investigates 3 different approaches to model the effect of annealing phenomenon in a welding process and its effects on the mechanical response of a FEM model. In the first approach, relaxation of equivalent plastic strains above the annealing temperature is considered. In the second, equivalent plastic strains as well as plastic strain components are annealed once the critical temperature is reached. In the third and last approach, equivalent plastic strains, all strain components and also stresses are reset to zero above the annealing temperature.

The FEM model is applied to a bead-on-plate weld case conducting a sequentially coupled thermal-mechanical analysis. Abaqus user subroutine UMAT has been developed in order to implement different annealing behaviours in the model.

Finally, FE analysis predictions of welding distortions and residual stresses are compared with experimental results. The third approach appears to be the most suitable technique to model the material relaxation at high temperatures.