Numerical modelling of residual stress redistribution induced by TIG-dressing

Paolo Ferro,Franco Bonollo,Filippo Berto,Roberto Montanari

doi:10.3221/igf-esis.47.17

Abstract

TIG-dressing is a technique used to improve the fatigue strength of welded joints by a remelting of the weld toe region that promotes both a smoother transition between the plate and the weld crown and a residual stress redistribution. These effects are very hard to be quantified by numerical simulation since a highly coupled thermo-fluid-mechanical analysis is required. However, if the final weld toe geometry is supposed to be known or a-posteriori measured, a simplified numerical method can be used to simulate the residual tress redistribution that uses the activation-deactivation function of elements. This technique is applied to a real steel weldment and results, in terms of phases proportions and residual stress redistribution, were found in good agreement both with data coming from metallurgical analysis and the improved fatigue strength observed on welded joints after the TIG-dressing operation.

Highlights

S everal studies have demonstrated that unwelded plain material shows a linear relation between static strength and fatigue strength, but that the presence of notches results in a reduction of the fatigue strength
Dahle [5] found an increase in fatigue strength at two millions cycles ranging from 10% to 90% according to the steel grade and being the largest increment obtained with high strength steels
Compared to the numerical models of welding processes developed in the last years [8,9,10,11,12,13,14], the numerical simulation of TIG-dressing process is complex because it requires a high coupling between thermometallurgical-fluid analysis and mechanical analysis

Summary

INTRODUCTION

S everal studies have demonstrated that unwelded plain material shows a linear relation between static strength and fatigue strength, but that the presence of notches results in a reduction of the fatigue strength. Some techniques, aimed to improve the fatigue strength of welded joints, were developed [1] They act mainly on two aspects: 1) the geometrical variation of the weld bead and 2) the reduction of the stress concentration factors. The weld bead geometrical variation induced by re-melting is influenced by the weldment distortions during TIG-dressing and vice-versa For this reason, it was recently published in literature a numerical model of the TIG-dressing process that simplifies a lot the computation by using the activationdeactivation function of elements [15]. It was recently published in literature a numerical model of the TIG-dressing process that simplifies a lot the computation by using the activationdeactivation function of elements [15] In this way, it is possible to avoid the fluid analysis, but the weld toe geometrical variation has to be ‘a priori’ known by means of welding and TIG-dressing trials. Such model is applied in this work to a real weldment and the results in terms of metallurgical and mechanical properties are compared and discussed

MATERIALS AND METHODS

RESULTS AND DISCUSSION

CONCLUSIONS