Detection of in-plane and out-of-plane fiber waviness in unidirectional carbon fiber reinforced composites using eddy current testing

In this paper, we propose a specialized probe to detect in-plane and out-of-plane fiber waviness in unidirectional carbon fiber-reinforced plastics and to characterize fiber orientations by an eddy current-based nondestructive technique. Experimental studies show that the proposed probe can detect in-plane fiber waviness with amplitude of 1.1 mm and length of 15.9 mm in a thin unidirectional carbon fiber reinforced plastic at sufficiently high drive frequency. The validity of the proposed method is verified through three-dimensional finite element method analysis. Variation in amplitude and phase of output signal obtained in numerical analyses qualitatively agreed with experimental results. Out-of-plane fiber waviness induced in a thick unidirectional carbon fiber-reinforced plastic can also be detected using the proposed probe. It is found that output signals in complex plane obtained during scanning a material with out-of-plane waviness become ring-shaped plots. Those plots in complex plane are used to identify the presence and location of out-of-plane fiber waviness.