Induction heating of unidirectional C/PAEK – A thermographic study on eddy current formation

Induction welding is an attractive assembly method for carbon fibre reinforced thermoplastic composites. Parts are heated through the electromagnetic induction of eddy currents in the electrically conductive network of carbon fibres. Such networks rely (partly) on interlaminar contact incidence between the carbon fibres for unidirectional ply-based composites, rendering eddy current formation stochastic. The present study aims to visualise this stochastic behaviour in order to gain deeper insights into the formation of eddy currents. To this end, various laminates were induction heated using a stationary coil while monitoring the heating patterns using a thermal camera. Similar behaviour was then replicated on ply-scale specimens using a strong direct current. The recorded thermograms highlight that eddy currents are predominantly induced along the different fibre directions present in the lay-up. Moreover, it was demonstrated that ply interfaces have a substantial impact on the (re)distribution of current density within the plies.