Managing distortion in welded structures using FEM

Sammanfattning: Welding as high productive joining method is widely employed in automotive, aerospace and shipbuilding industries. In practice, welding distortion brings about undesirable effects on production accuracy, appearance and strength of welded components. Thus, in order to increase the productivity and decrease the cost of the product, prediction and analysis of welding deformation are key factors in industrial context. Distortion of a structure can be measured experimentally; whilst in case of large or complex structures it is expensive and also time consuming. Numerical analysis is then performed using finite element method (FEM) that reduces the cost; however, in case of large welded structure and considering extremely nonlinear mechanical behavior of welding the computational expense incurred which must be cut through elastic analysis. In this sense, the residual plastic strain, namely inherent strain as a source of residual stress and welding distortion should be analyzed. The purpose of this study is to detail the prediction procedure of deformation in welded structure by elastic finite element modeling using inherent strain method. As a matter of fact inherent strain as an inelastic permanent strain or residual plastic strain, which exists in vicinity of fusion zone, is responsible for welding deformation and residual stresses. Comparing with elastic plastic analysis, inherent strain method has less computing time however the state of welding may be not investigated in detail; Furthermore, appropriate assumption of inherent strain region and determining the accurate values of inherent deformations in each typical joint bring about some limitations. On the other hand, just the elastic modulus and Poisson’s ratio at room temperature is used in elastic FEM, and there is no need for temperature material properties. So, at the present time, thermal elastic plastic finite element method can be used to predict residual stresses and welding deformations in small or medium structures but for large components elastic FEM is promising method.