Experimental electrical characterisation of carbon fibre composites for use in future aircraft applications

Abstract

This paper presents experimental testing of samples from two unidirectional Carbon Fibre Composite (CFC) panels to determine the factors that influence the electrical properties of CFCs and to also determine the temperature coefficient of resistance. The CFC panels were manufactured by two different techniques to compare the impact of the manufacturing process on the electrical properties. Various electrical conductivity measurement methods were evaluated to determine the most consistent and accurate technique. The influence of sample geometry on the measured electrical conductivity was also investigated. Thermal imaging was used to image resistive losses and illustrate the current paths through the fibres within the CFC test samples. Finally, the effects of increasing temperature on the CFC samples are presented, illustrating that CFCs have a negative temperature coefficient .

Three‐dimensional finite‐element analysis multiphysics modelling of electromagnetic Joule heating in carbon fibre composites

“…The percentage error was observed to be below 10% for both the UD and quasi‐isotropic 3D multiphysics FE models, which is considered good given the number of variables that need to be taken into account and the complexity of CFCs such as their anisotropic properties and lay‐ups, as discussed in Section 2. The good correlation between the simulation and experimental results can be attributed to the following reasons: The electrical experimental characterisation work conducted in [24] is complimented by the thermal characterisation work presented in this paper. This ensured the properties specified in the FE models were for the specific CFC samples used in the experimental test‐rig; The design of the test‐rig was based on the 3D modelling work.…”

“…This was evident from the current required to achieve the curing temperature using the UD samples compared to the quasi-isotropic samples. In [24], the authors investigated and presented the current flow through a UD CFC and the role that the interconnection points of the carbon fibre strands in the composite had on the heating pattern. In a UD sample, the return path for the induced eddy currents predominantly occurs at the ends, whereas in the quasi-isotropic samples each layer in the composite has carbon fibres angled at 45°f rom the previous layer; this results in more interconnection points and hence, increases the eddy current paths, resulting in reduced resistance.…”

“…• The electrical experimental characterisation work conducted in [24] is complimented by the thermal characterisation work presented in this paper. This ensured the properties specified in the FE models were for the specific CFC samples used in the experimental test-rig; • The design of the test-rig was based on the 3D modelling work.…”

“…Since the 3D model fidelity level selected was macroscopic, the electrical and thermal material properties inserted into the model could be the 'bulk' properties of the CFC's. The electrical properties such as the electrical conductivities in the fibre, transverse and through-thickness directions, respectively, and electrical temperature co-efficient were taken from the experimental characterisation work published in [24].…”

“…To simulate the temperature rise in a CFC due to induced eddy currents and the resultant power dissipated ( P eddy ), two analyses were required: an EM analysis, to solve the eddy current distribution in a CFC due to an applied external magnetic field; and, a thermal analysis to calculate the temperature rise from the power dissipated in a CFC due to the eddy currents. The electrical conductivities of CFCs are temperature dependent [24] and thus, the developed models also needed to incorporate this parameter. A feedback loop between the thermal model and the EM model was therefore necessary to update the electrical conductivities as the temperature increased.…”