Simplified distortion analysis for multi-pass welding using layered shell elements based on inherent strain

Abstract

Welding simulation is one of the most commonly used methods among all the types of simulations used in a shipyard. This is because the cost of reworking welding distortions significantly increases the construction cost of ships. In order to reduce the cost of the mitigation process, it is desirable to predict and subsequently avoid welding distortion. Currently, there are several methods that can predict the distortion of the welding, such as the equivalent load method based on the inherent strain, the strain as boundary condition (SDB) and composite shell method. However, those methods cannot be used for fillet welding used in multi-pass welding. Therefore, a new method to predict the welding distortion using layered shell elements for fillet joints, as well for butt joint has been developed. Based on the composite shell method, a solution was developed where the heat affected zone is divided into multiple layers in order to properly distribute the inherent strain throughout the thickness of the weld. In this research, a simplified method using shell elements that can predict the multi-pass welding deformation for the butt and fillet welding process is presented. This new approach can analyze the effects of geometric factors, such as groove shape, number of passes and plate thickness for multi-pass welding, especially for large structures used in offshore systems. To calculate the distortion of the multi-pass welding, increase the productivity and reduce the computation time, the thickness of the part is divided into multiple layers. For each layer, a different thermal expansion coefficient is applied according to the circumstances of each welding pass. This approach makes it possible to calculate for both members of fillet joint simultaneously. The method is compared with 3D thermal elastic plastic analysis, existing methods, as well as with experimental results.