Visualization and size estimation of fiber waviness in multidirectional CFRP laminates using eddy current imaging

This paper presents an eddy current method to visualize fiber waviness in multidirectional carbon fiber reinforced plastics. Since eddy currents induced by a driver coil flow along carbon fibers, waviness can be visualized if the eddy current path is visualized. We proposed a new complex plane analysis method to visualize an eddy current path from magnetic field measurements. The validity of the method was verified by finite element method analyses. Experiments were performed for multidirectional carbon fiber reinforced plastic specimens. In-plane waviness with misalignment angle from 6.9° to 24.9° were artificially induced in the specimens. An eddy current path was visualized from magnetic field data and it corresponded to the shape of induced waviness. The sizes of the wavy eddy current path were compared with waviness sizes measured by X-ray computed tomography and from optical images. Experimental results indicate that the surface waviness size can be estimated accurately, whereas the subsurface waviness size is underestimated.