A global thermo-mechanical model to mitigate welding residual stress and deformation in production of an aluminum bio-inspired AUV with a curved outside corner joint

Abstract

Welding mechanics of large-scale complex-shaped structures is generally either disregarded or implicitly presumed due to high complexity and time consumption — even in the case of numerical analysis, typically it is limited to local thermo-mechanical models of straight butt or tee welded joints. Nevertheless, not only is this study aimed at presenting a time-saving global thermo-mechanical model of a curved outside corner joint but also at exploiting combined effects of welding parameters to mitigate deformation and residual stress. The global thermo-mechanical model is thereby constructed by combination of shell and solid finite elements providing Thermal-Elastic-Plastic (TEP) analysis for an aluminum Autonomous Underwater Vehicle (AUV) of which novel hull shape inspired by catfish morphology results in a longitudinal curved outside corner welded joint. A suitable polynomial mathematical function enabled the welding heat source to move steadily along the curved path of the joint. Saving up computational time 3.5 times greater than conventional full 3D method, the global shell/3D TEP FEM is validated well against experimental temperature, distortion and residual stress distributions when locating the boundary between shell and solid elements with the size of solid zone up to the 3 times thickness of base metal based on accuracy of molten metal penetration, deformation and residual stress prediction. A stark difference of about 120% in maximum amount of longitudinal residual stress is observed between global and local models. Finally, optimal outcomes are employed in production of the AUV so that 33% reduction in welding speed mitigated residual stress by 22% whereas welding length and sequence were more effective on distortion.