Studies on Transient Stresses and Deformation Behavior of Groove due to Butt-Welds of Thin Mild Steel Plates (2 nd Report)

Abstract

In order to prevent cracking and to predict thermal stresses and distortions developed as a results of welding, it is necessary to know the details of thermal and mechanical response of weldments. While experimental measurements of the stresses and strains surrounding a weld heat source are very difficult due to high temperatures caused by welding, it has now become possible to analyse the transient stresses and strains in the immediate vicinity of the welded joints with an aid of the recent progress in analytical technique of the nonlinear problems by the finite element method.Most of the former works in this field are concerned with the analyses of bead-on-plate welds. In an attempt to refine our knowledge and improve the degree of correlation with reality, more realistic analytical models are developed for calculating temperatures, stresses and strains resulting from butt-welds of mild steel plates by use of the finite element method taking changes of the thermal and mechanical properties of the material with temperatures into account. We solved the unstationary heat conduction problems first and based on the calculated temperature distributions, we analysed the uncoupled thermal stress problems with time depending varying boundary conditions. The material subjected to the welding thermal cycle is postulated to behave mechanically as an isotropic, elastoplastic and strain-hardening continuum obeying the Mises yield condition and the Prandtl-Reuss flow rule.The elastoplastic stress distributions around a moving weld heat source, metal movements during welding and variation of forces and moments acting on tack welds are clearly presented. It has been shown that presence of root gaps play an important role in opening or closing behavior of groove and the magnitude of forces and moments acting on the tack welds ahead of the moving weld heat source. Some of the obtained results agree fairly well with experimental values.