Advanced mechanical characterization of friction stir welds made on polycarbonate

The influence of the welding and tool rotation speed on morphology and mechanical behavior of friction spot stir welds made on polycarbonate is investigated. The welds were performed in butt configuration. The mechanical behavior of the welds was assessed by means of tensile tests. Digital image correlation (DIC) analysis was performed to determine the strain distribution (over the cross section) during the tests. This enabled to determine the precise position of crack onset and simplified the determination of the welds' failure. These data were crossed with observation of the welds morphology to better understand the mutual relation among process conditions-morphology and mechanical behavior. The results indicated that the welds produced under low welding speed were characterized by adhesive failure between the stirred region and the substrate. The welds produced under higher speed were affected by excessive thinning. This led to failure in the stirred region or in some cases within the base material due to localized thinning. The mechanical characteristics of the welds were highly correlated to the temperature of the stirred region. This suggests the possibility to use IR thermography for online control and qualitative assessment of the mechanical behavior of the FSW welds made on amorphous thermoplastics.