Effect of tool geometry on mechanical behavior of friction stir spot welds of polycarbonate sheets

This study investigates the influence of the tool dimensions on the mechanical behavior of friction stir spot welds performed on polycarbonate sheets. Different tools were used by varying the pin geometry (cylindrical and tapered) and the diameters of the tool pin and that of the tool shoulder. Morphological analysis was conducted to determine the extension of the welded zone and main defects of the welds. Single lap shear tests were carried out to determine the influence of the tool dimension on the mechanical behavior of the welds. The onset and evolution of failure during the shear tests was analyzed. Five different failure modes were identified which showed both a brittle and ductile behavior. According to the achieved results, the strength of the welds reduced with increasing the pin diameter and taper angle. On the other hand, the strength increased with increasing the tool shoulder diameter. However, the highest specific strength, calculated as the ratio of the shear strength by the tool area, reduced with increasing the shoulder diameter. Under the optimal processing conditions, the strength of the joints reached up to 88 % of the shear strength of the base material.