Modeling and experimental evaluation of eddy-current probes for prepreg fiber waviness inspection

Despite numerous efforts to achieve in-line inspection of uncured carbon fiber during manufacturing, standard non-destructive testing methods have yet to meet this challenge. High-intensity eddy currents generated by a figure-8 shaped elongated transmitter coil follow the paths of carbon fibers, enabling visualization of fiber waviness. An innovative finite element modeling (FEM) approach was implemented for precise simulation of current density distortions caused by surface waviness. To validate the proposed FEM method, this paper presents experimental findings on optimizing a directional eddy current testing (ECT) probe to detect in-plane waviness at the top surface of carbon fiber prepreg, along with a discussion of application challenges. This study explores the creation of six ECT probes by adjusting the angle between receiver coils of varying aspect ratios. Sensitivity assessments were conducted to examine the probe's capabilities in detecting fiber features of interest. The results indicate that the selected probe design, featuring rectangular receivers and a 10-degree relative angle between receivers, is capable of in-line inspection of targeted defects with a signal-to-noise ratio (SNR) exceeding 70. The effects of varying lift-off distance up to 1 mm on the selected probe's sensitivity to targeted defects were examined, with optimal sensitivity observed at approximately 0.6 mm and a SNR exceeding 6.