COMPUTATIONAL MODELING OF RESIDUAL STRESS IN WELDS S. Yushanov* and K. C. Koppenhoefer* ABSTRACT Accurate prediction of stresses, strains, and residual stresses that are generated as a result of welding is important for a number of practical issues. Hydrogen-induced cracking, stresscorrosion cracking, distortion, as well as fatigue strength of welded structures can all be affected significantly by the residual stresses that are generated around welds. Due to the complexity involved in the experimental measurement of residual stresses, numerical simulation procedures are increasingly used for estimating the residual stresses that arise from welding. Commercially available simulation software readily allows one to account for the non-linearities due to variation of material properties and heat transfer coefficients with temperature. However, the material constitutive models available in most commercial packages do not account for some of the unique features associated with the welding process, e.g., material melting/remelting as different weld passes are deposited, solid phase transformation effects, etc. These features of the welding process influence the prediction of residual stress and distortion. However, the open literature does not include a systematic study of these factors. The work reported here uses a multiple-pass butt weld in a cylindrical pipe to study in detail the effects of advanced material modeling methods on residual stress. Deposition of material during the welding is carried out in multiple weld passes. At the melting temperature, all accumulated elastic and plastic strains are set to zero. The interaction of this strain zeroing with the isotropic and kinematic hardening is examined in terms of the effect on the distribution of residual stress and welding-induced distortion. KEYWORDS Residual stress, kinematic hardening, isotropic hardening, strain accumulation, welding, finiteelement analysis. INTRODUCTION Accurate modeling of the material response to welding represents a significant challenge in welding simulations ([1] and [2]). The large temperature change associated with welding generates a complex material response. These temperature changes produce difficulties in both the thermal and mechanical analysis in a welding simulation. However, the material response in a mechanical analysis represents a greater challenge than the thermal response to the numerical analyst. The mechanisms of plastic deformation and evolution of the yield surface during welding continues to be a point of discussion among organizations conducting welding simulations. To determine the influence of different techniques for modeling plastic deformation during welding, the International Institute of Welding (IIW) conducted a round robin of residual stress Edison Welding Institute, 1250 Arthur E. Adams Drive, Columbus, OH 43221 |