XFEM-based Numerical Analysis of Residual Stresses and Defect Nocivity in FSWeld AA6082-T6 Aluminum Alloy

Abstract

This work introduces a sequential framework integrating explicit thermomechanical finite element analysis with the eXtended Finite Element Method (XFEM) to evaluate the severity of residual stresses and defects in friction stir welded (FSW) AA6082-T6 aluminum joints. The thermal evolution and residual stress distributions are first computed in Abaqus/Explicit using a moving heat source model, validated against thermocouple measurements from the literature, with an average temperature deviation below 3%. A mesh convergence study confirms the reliability of the solution, showing less than 3% variation in the stress intensity factor (KI) between consecutive refinements. Subsequently, XFEM coupled with the Level Set method is employed to simulate crack growth under thermo-mechanical loading, following the maximum energy release rate (MER) criterion. Findings indicate that a rotational speed of 800 rpm lowers peak temperatures by 10% and longitudinal residual stresses (S11) by 30% relative to 1100 rpm. At elevated temperatures (~700 K), a significant increase in KI is observed due to pronounced thermal softening and degradation of material properties, highlighting the critical role of thermal effects on crack driving forces. This integrated approach enables a mesh-independent and accurate assessment of defect severity, providing a reliable tool for optimizing FSW parameters to enhance the structural integrity of aerospace-grade aluminum joints.