A theoretical approach to the residual stress assessment based on thermal field evaluation in laser beam welding

Residual stresses are one of the major issues in welded parts, since they could be detrimental to the integrity of components and structure. Their determination is rather complex and could be an arduous task, both when it is based on experimental methods and on numerical simulations. The proposed work presents a theoretical approach to the prediction of the longitudinal residual stress distribution, based on a parameterized multi-source model for thermal field simulation in laser welding previously introduced. Reference is made to the case of “keyhole” full penetration welding mode obtained by CO2 laser beam single pass on butt-positioned AISI 304L plates. The resolution of the thermal field allows the analytical calculation of the distribution of the longitudinal residual stresses in two ways: one makes use of a simplified formulation of the distribution well-known in the literature; a second modality makes use of a procedure for residual stress generation, which is based on a combined processing of thermal profiles and the corresponding heating–cooling cycles calculated in single points as their distance from the welding axis varies, and provides a complete characterization of the distribution of longitudinal residual tensile stresses. After the introduction of thermal field modeling, both the proposed residual stress calculation procedures are detailed, applied to the analyzed case, and validated, highlighting the differences in the approaches and results.