Fracture behaviour of friction stir spot welded joint

The fracture behaviour of lap-shear joints manufactured by friction stir spot welding (FSSW) technique is examined in this paper. Two aluminium sheets of 2.8 mm thickness were welded using different process parameters to form a lap-shear joint. Special tool was designed and fabricated for the stir-spot welding process. Tensile-shear tests were performed to determine the tensile-shear load bearing capacity and toughness of the weld. the stress intensity factor and the J- integral around a weld are determined in order to characterize the fracture behavior. the effect of different main process controlling parameters, e.g., the tool prop pin rotating speed, duration action time and sinking/penetration depth into the lower welded sheet on the weld fracture behaviour has been investigated through an intensive experimental program. Optical and scanning electron microscopes fractographes were obtained to examine the weld fracture modes. the results show that higher frictional heat due to relatively higher tool probe pin rotational speed and penetration depth into the lower sheet produces improved joint static strength and toughness.