A.R Shahani - Professor, Department of Applied Mechanics, K.N. Toosi University of Technology, Tehran, Iran
A Farrahi - PhD student, Department of Applied Mechanics, K.N. Toosi University of Technology, Tehran, Iran

The effect of sheet thickness on the static strength and fatigue behavior of the friction stir spot welding of Al6061-T6 alloy have been investigated experimentally using the lap shear specimens. Three different sheet thicknesses of2, 3 and 4mm have been studied, whereas the other welding parameters had been kept constant. According to theresults of static experiments, specimens show higher strength by decreasing of sheet thickness. The comparison offatigue behavior of the three different welding conditions, reveals that lower thicknesses endure more cycles in the sameapplied stress. Also the slopes of curves become higher with the decrease of sheet thickness, i.e. at the low load levels,three welding states show more similar behavior than the high load ones. Generally, the fatigue failure of friction stirspot welds is different in the various load levels. At the higher load levels the final failure has been caused by thecircumferential crack growth but at the lower load levels, the kinked crack growth and transverse final rupture is themajor cause of failure. In the present research, this kind of failure just occur in the specimens of 2mm thickness whilein the two other thicknesses the only failure has been observed is the circumferential crack growth.

Friction Stir Spot Welding, Fatigue Failure, Effect of Sheet Thickness