Fiber Orientation Assessment on Laminated Carbon Fiber Composites using Eddy Current Probe

Abstract

Fiber orientation is a crucial feature of carbon fiber reinforced composite materials, with fiber layup chosen to achieve optimum part performance in the load environment for which the part is designed. This is especially important for compression molded composite parts, where fiber orientation can change during the molding process. Therefore, good quality control requires verification that the manufactured part meets design specifications, and a rapid technique to verify orientation of carbon fiber plies is needed. In this paper, a technique using a flexible eddy current sensor is proposed to assess the fiber orientation. The directional eddy current sensor is configured to measure part conductivity as a function of applied current direction. Experimental results show a correlation between the peaks in the measured conductivity as a function of angle and the fiber orientations in the part. This nondestructive evaluation (NDE) technique has a fast inspection rate and is relatively cost effective. A four-layer quasi-isotropic carbon fiber composite made by compression molding was used to calibrate the system in this study. Several specimens were fabricated with nonsymmetric ply layups using unidirectional preimpregnated carbon fiber with varying orientations. These specimens were tested using the calibrated system. The final fiber orientations in the specimens were confirmed by cross sectional microscopy and microfocus X-ray computed tomography analyses.