Colloquia

Summary

In recent years, composite material is adopted in the aerospace industry as a lightweight, high strength and stiffness, alternative to conventional materials for structural applications. Early adoption of composites in the aerospace industry has been primarily focused on thermoset composites. Thermoplastic composites offer advantages over these thermoset composites. One of these advantages is the ability to assemble parts in a larger structure using fusion bonding processes, which are generally more cost-effective than the alternative assembly methods. Induction welding is one of the available fusion bonding methods. Here, heat is generated in a workpiece by means of eddy currents induced by an alternating magnetic field. The generation of these eddy currents depends on the conductive network of fibres within the composite material to form conductive loops.

To predict the heating behaviour of a thermoplastic composite workpiece, simulations need to be carried out. These simulations can subsequently be used for the optimisation of the induction welding process settings or the welding setup. One of the input parameters for the simulation is the anisotropic electrical conductivity of the composite material. These can be obtained experimentally.

However, currently no standardised method exists for the characterisation of the electrical through-thickness conductivity of uni-directional thermoplastic composite plies or laminates. Additionally, existing data on the through-thickness electrical conductivity of uni-directional thermoplastic composites is scarce. Therefore, within this graduation assignment, methods obtained from literature have been implemented and evaluated based on a list of wishes and demands. A six probe method with transverse samples has been proposed to characterise the electrical through-thickness conductivity of uni-directional thermoplastic composites. Additionally, two probe characterisations have been performed for verification. A characterisation of the through-thickness conductivity of the material from three material suppliers could be established. Furthermore, the sample morphology has been pointed out to strongly affect the through-thickness electrical conductivity of the uni-directional thermoplastic composite laminates.