Automated Foreign Object Detection for Carbon Fiber Laminates Using High-Resolution Ultrasound Testing

Abstract

Carbon fiber laminates are becoming popular in the manufacturing industry for their many desirable properties; like good vibration damping, high strength to weight ratio, toughness, high dimensional stability, low coefficient of thermal expansion, etc. During the manufacturing process, undesirable foreign objects, such as peel-ply strips, gloving material, Kapton film, etc. can be introduced into the part which can lead to a localized weakness that is a function of the FOD material and geometry. These manufacturing defects can act as stress concentration points and sometimes cause catastrophic failure. In this study, a method using pulse-echo ultrasound testing is used for the detection and quantification of the dimensions of foreign object debris (FOD) within carbon fiber laminates. This study presents a method to create high-resolution c-scans, and from the full-waveform dataset extract the FOD depth and planar dimensions with an automatic edge detection technique. Results from three carbon fiber laminates are investigated with embedded foreign objects ranging from 1.5 mm to 12.7 mm in the effective diameter, with error in quantification from the ultrasound data of 0.2 mm to 0.36 mm. CT imaging is used to confirm the FOD was not altered during manufacturing, and the as manufactured FOD dimensions were equal to the as designed FOD dimensions to within the resolution of the CT configuration utilized in the study. Of importance for the ultrasound inspection, in every case the FOD is detected, the layer depth is properly identified, and the spatial dimensions of the FOD are quantified to within 0.36 mm. This work is the first stage of a larger project leading to an FAA 8110-9 for FOD identification within a laminated composite.