Induction Heating of UD C/PAEK: What Thermography Can Teach Us about Eddy Currents

Induction welding is an attractive technology for fusion bonding of carbon fibre reinforced thermoplastic composites. In this process, eddy currents are induced in the conductive carbon fibre network by an alternating electromagnetic field, heating up the parts. In unidirectional ply-based composites, formation of eddy currents relies on the ply interfaces where changes in the fibre orientation facilitate closed-loop conductive paths. Improved control of the welding process therefore requires a deeper understanding of how the fibrous architecture relates to the physical mechanisms governing heat generation, which is the focus of this work. It comprises induction heating experiments on thin laminates and a series of tests performed on ply-scale specimens subjected to a strong electric current. Resultant heating has been monitored using an infrared camera. Combined, the recorded thermograms highlight that eddy currents are dominantly induced along the different fibre directions present in the lay-up and that the varying quality of fibre contacts at the ply interfaces affects the homogeneity of the current density within the plies

1D squeeze flow analysis of chopped long fibre thermoplastic composite

Long fibre thermoplastic (LFTs) in the form of chopped tapes are well known as they combine relatively high mechanical performance and good formability compared to respectively short and continuous fibre reinforced composites. Complex shapes can be manufactured with high fibre content with compression moulding [1], which makes these thermoplastic composite chopped tapes a good candidate for industrial applications. During moulding, the flow of fibre reinforced polymer leads to an altered fibre orientation distribution which affects the final mechanical properties of the part [1-4]. In order to predict the mechanical performance, it is therefore important to understand the mould filling behaviour of the LFTs. In spite of being used in the industry for quite a long time, the complex flow behaviour of LFTs in processes like compression moulding is still a challenge to predict. Although the flow in the compression moulding process is usually limited, it is critical for the final part quality. In flat geometries, it is not known whether flow during mould filling is affine/single-phase where polymer and fibres move together or dual-phase where they move separately, which can result in fibre-matrix separation. In order to model the compression moulding process, one needs to know either single- or dual-phase flow is applicable. The objective of this work is to investigate the separation of the resin from fibres and to realize this objective, 1D squeeze flow experiments are performed in a flat geometry. Chopped unidirectional tapes of carbon/polyethersulfone were used for the experiments. Different processing conditions were used in experiments with a mould which was filled only partially. A burn-off method was used to analyze the fibre mass fraction. The samples for the burn-off test were taken along the flow direction. Results of polymer burn-off did not show significant changes in the fibre mass fraction along the flow direction and therefore the flow can be assumed to behave as a single-phase flow