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Electromagnetic Interactions with Composite Materials

Khan, Jameel Bradley

[Thesis]. Manchester, UK: The University of Manchester; 2018.

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Abstract

The use of Carbon Fibre Composites (CFCs) in the aircraft industry has increased significantly. Over 50% of the structural material used in modern aircraft design is composite materials because of its weight and tensile strength advantages over the traditional materials used. An area of interest is the repair of damaged CFCs. This thesis investigates the possibility and feasibility to electromagnetically achieve the curing temperature required for repair of CFCs. The properties of CFCs are a key factor in determining if it can be repaired electromagnetically. Due to the lack of publications in this area, this thesis experimentally characterised the electrical and thermal properties of CFCs. The results illustrated that the electrical and thermal conductivities of CFCs are highly anisotropic. The experimental work also illustrated a key factor, i.e. CFCs have a negative temperature coefficient. The modelling methodology taken in this thesis is a combination of analytical and three-dimensional (3-D) finite element (FE) models. This methodology provided the step by step validation required to understand such a complex problem. The final model is a 3-D FE multiphysics model. This model was used to exam the level of eddy currents required to achieve a measureable temperature rise in CFC samples. An empirical equation was derived to simplify the relationship between the input current and frequency, to the maximum temperature in the CFC samples. An electromagnetic (EM) test-rig unit was designed and built successfully. The EM test-rig unit validated the predicted results from the 3-D FE multiphysics models. This thesis illustrated that the curing temperature of CFCs can be achieve electromagnetically without the use of electrically conductive additives added into the resin contrary to the publications. This novel approach removes the hazards created by electrical conductive additives in a repair patch and offers a practical solution for in-situ high quality composite repair of complex engineering structures. Finally, this thesis combines the validated 3-D models with the EM test-rig unit to design a model base approach to EM repair of CFCs.