# Modelling Eddy Current Testing of Gaps in Carbon Fibre Structures Based on Spline Approximation

## TL;DR

This paper introduces a new modeling approach for detecting gaps in carbon fiber structures using eddy current testing and spline approximation.

## Contribution

A novel finite element modeling approach using spline approximation to better account for fiber heterogeneity and inter-laminar current paths.

## Key findings

- The electromagnetic properties of carbon fiber structures with gaps can be successfully modeled using the proposed approach.
- Simulation results are validated by comparing virtual scans with actual eddy current scans of carbon fiber fabric with and without gaps.

## Abstract

Defects such as gaps, delamination, and the misalignment of fibres impair the performance of carbon fibre-reinforced composites and can lead to structural failure during operation. Eddy current testing has proven to be a suitable method for detecting these defects early in the manufacturing process. However, validated electromagnetic modelling techniques are required to develop new eddy current sensors and gain a better understanding of the eddy current signals caused by different defect sizes. This paper proposes a novel finite element modelling approach to better account for fibre heterogeneity using spline approximation. Further, adaptive mesh refinement is used to reduce FEM solution errors. A defect in the form of a gap is modelled by adjusting the spline approximation accordingly. Finally, the model also accounts for inter-laminar current paths between carbon fibre layers, which are determined by four-terminal resistance measurement. The results show that the electromagnetic properties of the structure can be successfully modelled. The simulation is validated by comparing the virtual scans with eddy current scans of dry carbon fibre fabric with and without artificially manufactured gaps.