Effect of Weld Pass Sequencing On Temperature Distribution and Residual Stresses in Gmaw

Abstract

The intense localized heating and cooling in the fabrication of welded joints leads to residual stresses and distortion and this reduces the service life of the joint. Prediction of levels of residual stresses before actual fabrication of the joint is necessary to avoid problems associated with residual stresses after fabrication. Weld pass sequencing is one of the methods to reduce residual stresses in the welded fabrication. Finite element method is an alternative method in preference to costly experimental procedures like strain gauging and X-ray diffraction in the estimation of residual stresses. Sequential thermo-mechanical analyses have to be carried out for the prediction of residual stresses using FEM. In this work a thermo-elasto-plastic analyses are carried out to determine the levels of residual stresses in normal welding and skip step welding for various welding conditions of bead on plate welding of mild steel plates. Goldak’s double ellipsoidal heat flux density distribution to model the moving heat source. Non-linear thermo-mechanical properties have been used to compute temperature distribution and residual stresses. Filler element addition is accomplished by element birth-death technique. Kinematic hardening is used to model post elastic behaviour of mild steel. Online thermal cycles of a point on the base metal are captured by thermocouple measurements. The comparison of experimental and numerical thermal cycles yielded good agreements. Longitudinal residual stresses are dominant in normal welding and skip step welding. The comparison of longitudinal residual stresses in normal welding and skip step welding indicated that peak values of these stresses reduced with skip step welding.