Foreign Object Identification within a Laminated Carbon Fiber Composite Using Pulse-Echo Ultrasonics

Carbon fiber composites are becoming increasingly popular in a wide variety of industries including aerospace, automotive, and athletics. During manufacturing, foreign objects such as loose peel ply, bagging materials, etc. may embed themselves between laminae causing localized weaknesses, crack initiators, and stress risers. This has created a need to characterize these composite parts and identify these defects in a nondestructive manner. This research improves upon existing technologies for identifying foreign objects within carbon fiber composites. To simulate embedded foreign objects within a composite structure, Polytetraflouride (PTFE) inclusions were placed between laminae during manufacturing to simulate a manufacturing induced foreign object. The embedded inclusions measure 0.002 in. (0.05 mm) in thickness. Making use of a custom in‐house ultrasonic immersion scanner, several techniques are presented in this work to identify PTFE inclusions based off of the resulting c‐scan data using custom MATLAB code. Results show that circular inclusions with a radius as small as 0.07 in. (1.9 mm) in can be identified, with the highest contrast for identification coming from the presented spatial averaging technique. In addition, the location of the object within the laminate stack can be determined, and results are presented for a 10 lamina composite with a successful identification of foreign objects throughout the entire part.

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