An Approach to Modelling Friction-Stir Welded Joints in Forming

The use of multi-material components in the automotive industry is increasing, driven by the demand for lightweight construction to reduce emissions. Tailor-welded blanks, which adapt material thickness and property locally for strength and weight optimisation, offer a promising approach. Friction-stir welding (FSW) facilitates the joining of different materials with varying thicknesses, addressing weldability challenges. This study focuses on finite element modelling of the formability of friction-stir welded blanks. Formability tests were conducted to evaluate potential failure modes of the welded joints. These tests indicated that the modelling of the joint interface at the border of the stirred volume is a crucial extension to the necessary material models for the base materials and the stirred volume within the welding seam. The cohesive zone model implemented in LS-DYNA was identified as an effective method for representing the joint interface, as it accommodates mixed-mode elastoplastic loading, including shear and normal tractions. Material parameters for plasticity and damage in the base materials, the stirred volume, and the cohesive zone model were calibrated. Validation of the model through deep drawing simulations, compared with experimental results, demonstrated a good correlation, confirming the proposed modelling approach's capability to predict the formability of friction-stir welded blanks.