Study on Fe-SMA-steel TIG welded lap joints for structural reinforcements

Iron-based shape memory alloy (Fe-SMA) is a promising reinforcement material due to its unique shape memory effect (SME) and weldability. By pre-stretching and thermally activating Fe-SMA attached to steel structures, prestress can be effectively achieved. This study employed ABAQUS to evaluate temperature distribution, residual stress, and mechanical performance of the Fe-SMA-steel TIG welded lap joints, considering potential mechanical performance alterations of the joint induced by the TIG welding process. The heat source model, heat transfer model, failure modes, load-displacement relationship, and stress-strain relationship were validated against experimental results, showing good agreements. The validated numerical model was then used to investigate the temperature field, residual stress, and joint mechanical properties considering corresponding parameters. Increasing the thickness of Fe-SMA and steel plates significantly enhanced the ultimate load and initial stiffness of the joints, although the growth rate slowed when the steel plate thickness exceeded 6 mm. Compared with altering the thickness, improving steel strength had a less pronounced impact, while the Q235 plate exhibited premature failure due to its low strength. In the present study, a weld length of 30 mm was recommended to achieve sufficient ductility and loading-bearing capacity for structural reinforcement applications. Based on the results above, the formulas in Chinese standard GB 50017–2017 for steel structures were modified, which demonstrates errors within 10 % compared to experimental and numerical results. In summary, this study provides design references and practical tools for the application of Fe-SMA plates in reinforcing steel structures via TIG welding.