Carbon fibre reinforced polymer (CFRP) composite materials are widely used in many applications, such as aerospace, automotive, shipbuilding and civil engineering, due to their relatively low density, high mechanical strength, and flexibility. These characteristics are determined by the proper stacking of various layers of carbon fibres oriented at different angles and by the curing process. In these multi-layer structures, fibre misorientation (off-axis) and fibre waviness can happen during the manufacturing process, leading to reduced performance and structural failures during operation. The high-frequency ECT has demonstrated its capability for detecting in-plane waviness by using a transmitter-receiver (Tx-Rx) probe in previous work. However, the electromagnetic modelling of waviness was not fully explored in the community, which hinders the optimisation of the ECT configuration for achieving high detectability and sensitivity. In this paper, firstly, the electromagnetic behaviour of in-plane waviness was modelled as the interpolation function of maximum waviness angles, wavelength and location. Secondly, the crucial experimental parameters of operation frequency and scanning orientation are quantitively investigated and optimised. Thirdly, a new configuration consisting of a ferrite core rectangular Tx coil and two differential Rx coils is investigated to demonstrate its improved waviness detectability and sensibility by generating uniform eddy current density along with fibre direction. The current results demonstrate indicate that: 1). waviness increases the electrical response of the CFRP using the Tx-Rx coil, which is due to the increased current density J; 2). The phase information of the Rx coil can characterise the maximum waviness angles and wavelength; 3) The ferrite core rectangular Tx-Rx setup shows a 40% increase in terms of the eddy current density, and the uniform distribution of the eddy current allows the enhanced capability of the location and characterisation of the defect.

Investigation of the Modelling of Fibre Waviness Using High-Frequency Tx-Rx Eddy Current Technique

Paper Proceedings: https://asmedigitalcollection.asme.org/qnde/QNDE2021/volume/85529

ASME 2021 48th Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE2021)

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