Experimental and numerical analysis of eddy current sensor signal induced by out-of-plane fiber waviness in carbon fiber composites

Eddy current sensor signals induced by out-of-plane waviness in carbon fiber composites were investigated. Cross-ply laminates with artificial out-of-plane waviness were fabricated. The samples were scanned using an eddy current probe to measure the in-phase and quadrature phase components of the pickup coil voltage with respect to the excitation. A two-dimensional map of the pickup coil voltage amplitude indicated that it was difficult to distinguish signal changes in the waviness zone from signal changes caused by inhomogeneous electrical properties. By selecting the optimum image phase and probe rotation angle, the signal-to-noise ratio was improved greatly and the waviness was visualized without being masked by signal changes in the non -defective zone. Finite element analysis of eddy current testing was performed for various waviness amplitudes and wavelengths to obtain the relationship between the waviness dimension and the pickup coil voltage. The finite element analysis validated the enhanced sensitivity to waviness observed experimentally.