Experimental investigation of the resistance welding for thermoplastic-matrix composites. Part I: heating element and heat transfer

A comprehensive experimental investigation of the resistance welding of car bon-fibre and glass-fibre reinforced polyetherimide (PEI) laminates is pres ented. Lap-shear and double-cantilever-beam specimens were resistance welde d by using fabric and unidirectional heating elements. The statistical dist ribution of the resistance of the heating elements was characterised, and t he effects of the temperature on the heating element resistance were evalua ted. The influence of the mechanical contact pressure on the contact resist ance was also investigated. One of the main process parameters in resistanc e welding, i.e. the power density, was studied in detail. Heating uniformit y in the heating elements was assessed through thermal imaging, allowing fo r a comparison between fabric and unidirectional heating elements. Temperat ure histories were measured and compared to those simulated by a three-dime nsional transient heat transfer finite-element model. Factors limiting the size of the welded joint, i.e. temperature non-uniformity within the weldin g area and current leaking to the laminate, were investigated. Proper elect rical insulation using a glass-fibre/PEI interlayer between the heating ele ment and the laminate when joining carbon-fibre/PEI laminates effectively e liminated current leaking and enabled large-scale resistance welding. (C) 2 000 Elsevier Science Ltd. All rights reserved.