Non-contact Visualization of Fiber Waviness Distribution in Carbon Fiber Composites Using Eddy Current Testing

Abstract

Fiber waviness is one of the process-induced defects that causes significant reduction in compressive strength of carbon fiber composites. In this study, eddy current techniques for noncontact visualization of waviness distribution are newly developed. In-plane waviness in a carbon fiber composite is visualized by visualizing the path of the eddy current flowing along the carbon fiber through magnetic field measurements. Finite element analyses show that the shape of in-plane waviness can be visualized in the distribution of the magnetic field from the eddy current. However, it is found that in-plane waviness with a smaller angle than the actual misalignment angle is visualized as the distance between tested material surface and measurement plane increases. To avoid the underestimation of the waviness angle in non-contact measurements, a magnetic imaging method to reconstruct the surface magnetic field is proposed. The magnetic field on the sample surface is reconstructed using the magnetic field data obtained in the area away from the surface. Experiments were performed for a cross-ply laminate with an artificially induced in-plane waviness. The distribution of in-plane waviness can be successfully visualized from the measured magnetic field. The angle of waviness can be measured with an error of 1° using the proposed magnetic imaging method for non-contact measurements.