2. Experimental procedures
Two stages of experiments are involved in the study. First are fundamental trials with an objective of establishing whether the C-scan technology is feasible for NDT of resistance spot welds in aluminium. During fundamental trials, spot welds were initially examined in the as welded condition; then the same samples were re-examined after removal of the surface indentation by milling the surface with a 15 mm cutter. The spot weld locations were easily discernable in first instance by the surface indentations commensurate with the 50 mm spherical radius of electrodes; and subsequently by the concentrically surface milled area, which allowed the ultrasonic scanner to be positioned symmetrically about the weld. Upon success of the fundamental trials, advanced trials were carried out to validate the NDT technique on resistance spot welds in real assemblies. A conventional rechargeable hand tool with a 20 mm abrasive disc attachment was used to provide a flat ground sheet surface. Following NDT, all welds were either destructively peeled to reveal the weld plug diameters, or sectioned for metallographic examination for comparison with the ultrasonic test results.