Experimental investigation and numerical modeling of the fatigue crack growth in friction stir spot welding of lap-shear specimen

In this research, the fatigue behavior of the friction stir spot welding (FSSW) is analyzed experimentally and numerically in the lap-shear specimens of Al 6061-T6 alloy. The micro-hardness, static and fatigue experiments are performed to investigate the mechanical behavior of the FSSW. Two fatigue failure modes are observed at different load levels, including shear fracture at high load levels and transverse crack growth at low load levels. The welding process is modeled using the coupled Eulerian-Lagrangian thermo-mechanical technique in order to predict the residual stresses. The fatigue life of FSSW is evaluated by a three-dimensional finite element re-meshing model using Zencrack software, which considers the evaluated residual stresses. Three-dimensional determined crack profile shows good agreement with the experimental fractured surface. The results of this investigation are compared with the available numerical and theoretical models and reveal better agreement with the experimental results due to the three-dimensional re-meshing modeling of crack growth and considering the residual stresses. The most previous models have considered constant kink angle and stress intensity factors during the crack growth. The results of this study approved that these assumptions are not appropriate.