Current leakage prevention in resistance welding of carbon fibre reinforced thermoplastics

Current leakage is a concern with resistance welding of carbon fibre reinforced thermoplastic composites. This phenomenon is particularly important when unidirectional adherends, with the carbon fibres parallel to the electrical current direction, are welded. In this investigation, a new electrically-insulated heating element consisting of a ceramic-coated (TiO2) stainless steel mesh was developed to prevent current leakage. Special specimen geometry, called a skin/stringer configuration, was welded with this newly developed heating element to represent typical reinforced aerospace structures. The adherends were made of APC-2/AS4 (carbon fibre/PEEK) composites. Unidirectional specimens, which represent the most critical case, were first welded using the new heating element. The insulated heating element successfully prevented current leakage and showed great improvement in temperature homogeneity over the weld area. The impact of the new heating element on the mechanical performance of the welds was then assessed by welding quasi-isotropic specimens. The mechanical performances of quasi-isotropic specimens welded using the new insulated heating elements and conventional (non-insulated) ones were compared under short beam and three-point bending tests. No mechanical performance drawback was observed with the new heating element; however, the failure mode of the welded quasi-isotropic specimens was changed from a delamination in the skin laminate failure to a weld interface debonding failure. (C) 2007 Elsevier Ltd. All rights reserved.