The influence of phase transformations on residual stresses induced by the welding process—3D and 2D numerical models

Abstract

In this work, a numerical study of laser beam welding of steel was performed. In particular, phase transformation effects were considered, which consist mainly of volume change and transformation plasticity. Thanks to the possibilities of numerical modelling, additional analyses were performed (a) without taking into account phase transformations and (b) considering only the transformation plasticity phenomenon.The aim of this study was to examine the influence of phase transformation on the residual stress induced by the welding process, by comparing the results obtained with the described differences in the analyses. Finally, the residual stress field computed by the three-dimensional (3D) model was compared with the one computed by a two-dimensional (2D) model in order to estimate the grade of reliability of the more efficient 2D analyses, also in the presence of phase transformations. It was found that both volume changes due to phase transformations and transformation plasticity have a great influence on the residual stress induced by the welding process. 2D numerical models can be used with good accuracy instead of 3D models, if the in-plane stresses are of primary interest. All analyses in this investigation were performed with the finite element code SYSWELD®.

A 3D dynamic analysis of thermal behavior during single-pass multi-layer weld-based rapid prototyping

“…The thermal conductivity is artificially increased for the compensation of convection stirring effect in the molten pool (Lindgren, 2001). Furthermore, the latent heat of phase change is considered by modifying the specific heat curve with the change of temperature (Ferro et al, 2006).…”

Numerical sensitivity analysis of welding-induced residual stress depending on variations in continuous cooling transformation behavior

“…5(a), exhibit essentially the same residual stress level at the weld centerline, but while approaching the fusion line there is a discrepancy between a constant level for the case neglecting large deformations and the decreasing residual stress level for the case of large deformations. The behavior represented by the large deformations calculation does not correspond to usual residual stress evolution in plain carbon steels [6,[33][34][35]. A higher stress level in the weld would assume a strain hardening effect that is larger in the weld than in the HAZ.…”

“…In recent years, the on-cooling phase transformation behavior has been integrated in finite element simulations of steel [4][5][6][7][8]. These studies have all shown the strong effect of the austenite to martensite transformation on the final residual stress state.…”

The fatigue behavior of V-notches in presence of residual stresses: recent developments and future outcomes

“…During solidification and cooling of a multi-phase material, the variation of the specific volume and the 'transformation plasticity' [22] associated to phase transformation, influence the thermal and residual stresses induced by thermal loads. It was shown that such effects are so high that any numerical model of welding process that doesn't take into account phase transformation effects fails in calculating the thermal and residual stress filed [26]. When the scale of observation is focused on about one tenth of the notch depth, it was observed that phase transformation changes the sign of residual stresses if compared to the results obtained in a simplified mono-phase material [20].…”