Predicting induction heating of tape-based thermoplastic composites: The role of orthotropic electrical conductivity

Induction welding offers aerospace industry efficient assembly of sub-structures from individual thermoplastic composite (TPC) parts. Despite the commercial success for woven fabric-reinforced TPCs, the adoption of induction welding for unidirectional (UD) ply-based parts significantly lacks behind in comparison. Induction heating is based on the electromagnetic induction of eddy currents in the carbon fibre network. For UD ply-based TPCs, these currents rely, in part, on coincidence of fibre-fibre interactions, resulting in a high sensitivity of the process to small variations in the material and its processing history. This sensitivity does not align well with the present approach to process window development, part, and tool design, which relies on empirical procedures and practical know-how. Predictive induction welding simulations are therefore necessary to greatly enhance process understanding and streamlining the iterative readjustment for optimal process parameters.

The dissertation aims to enable accurate prediction of the induction heating in UD ply-based composites through physics-based numerical simulation. To this purpose, the characterisation of orthotropic electrical conductivity is investigated, focusing on the identification of typical variations in the stochasticity-driven electrical properties. The material data is subsequently implemented in COMSOL Multiphysics for prediction of the stationary induction heating response of various different lay-ups. Simulations are experimentally validated using infrared thermography. Furthermore, the validated numerical modeling framework is used for a sensitivity analysis on these induction heating patterns, thereby greatly improving our understanding of the origin of process sensitivity during induction welding and providing potential paths for improvement of process stability.