Resistance welding of thermoplastic composites skin/stringer joints

An experimental investigation of resistance welding of APC-2/AS4 PEEK/carbon fibre composite using a stainless steel mesh heating element is presented. A special specimen geometry, the skin/stringer configuration, was used to represent a typical reinforced aerospace structural joint. The specimens consisted of a flange, representing a stringer or frame, welded onto a skin laminate. The effects of the welding parameters such as the input power level and clamping distance on the weld quality and performance were investigated. The welding parameters were optimised using short beam shear tests, ultrasonic C-scan inspection and optical microscopy. The mechanical performance of the resistance-welded skin/stringer configuration was investigated using three- and four-point bending tests and the failure mechanisms were characterised by optical and scanning electron microscopy. Two methods were used to reduce the stress concentration at the flange tip. The first method was to machine a 20° taper angle at the edge of the flange and the second one was to create a resin fillet at the flange tip. No mechanical performance improvement was obtained with the resin fillet method but the taper angle method showed 25% mechanical performance improvement when the taper angles were machined after the welding operation.