Characteristics of resistance welding of lap shear coupons. III. Crystallinity

A transient three-dimensional heat-transfer, consolidation and crystallinity model for the resistance welding of thermoplastic-matrix composite lap-shear specimens is established. The heat-transfer model assumes orthotropic heat conduction in the composite parts and includes heat losses by radiation and natural convection. For the APC-2 laminate/PEEK film welding configuration, three crystallisation kinetics models are compared during the cooling stage of the resistance welding process. Cooling rates are predicted for natural cooling and the total processing time is determined. A coupled crystallisation kinetics /crystal-melting model is developed to predict the final crystallinity level in the welded joint. The effect of power level on the final crystallinity in the joint is investigated. Latent heat due to crystallisation and crystal-melting events is predicted and taken into account in the heat-transfer model. The influence of the environmental temperature on cooling rates and on the final crystallinity level in the joint is discussed. For the CF-PP laminate/PP film welding configuration, final crystallinity levels are predicted and compared with experimental data.