Non-contact visualization of fiber waviness distribution in carbon fiber composites using eddy current testing

Abstract

Fiber waviness is a process-induced defect that greatly decreases the compressive strength of carbon fiber composites. In this study, we developed eddy current techniques that enable non-contact visualization of waviness distribution. To visualize in-plane waviness in a carbon fiber composite, we visualized the path of eddy current flowing along the carbon fiber by measuring the magnetic field. Finite element analyses show that the shape of the in-plane waviness can be visualized in the distribution of the magnetic field from the eddy current. However, with increasing distance between the surface of the tested material and measurement plane, the visualization increasingly underestimates the in-plane waviness angle. To avoid this underestimation, we propose a magnetic imaging method that can reconstruct the magnetic field at the surface. The surface magnetic field was reconstructed by using the magnetic field data measured away from the surface. Experiments were performed on a cross-ply laminate with artificially induced in-plane waviness. The distribution of in-plane waviness can be successfully visualized from the measured magnetic field. Using this magnetic field imaging method to enable non-contact measurements, the angle of waviness can be measured with an error of only 1°.

Keywords:

• carbon fiber composite
• non-destructive testing
• waviness
• eddy current