Evaluation of carbon fiber laminates via the use of pulse-echo ultrasound to quantify ply-stack orientation and manufacturing defects.

The use of carbon fiber composites have become more prevalent. Laminated composites provide advantages over traditional materials as the final properties of the part can be tuned. These materials also provide new challenges relating to testing and validation. Traditional testing methods are destructive in nature, creating additional costs. Non-destructive testing can be used to verify the safety of composite parts. This research addresses challenges in the quantification of the ply stack of laminated plain-weave carbon fiber composites and the detection and sizing of foreign objects within carbon fiber laminates via the use of pulse-echo ultrasound. The first scientific contribution of this work is a method to determine the number of lamina and orientation of each lamina for plain weave carbon fiber laminates. Current methods to verify the ply stack are destructive, increasing product waste and costs. The method developed uses pulse-echo ultrasound causing no damage to the inspected part. The method is demonstrated by analyzing 12 unique laminates ranging from 3 lamina to 18 lamina in thickness. The ply stacks represented are also varied. The technique accurately determines the number of lamina and correctly predicted the orientation of 115 out of 117 plies within ±3° of the true orientation. The second scientific contribution of this work is the development of a method to detect and quantify foreign objects in carbon fiber composites. Foreign objects create localized weakness within the composite leading to safety concerns. The method presented can detect various materials of concern common to a manufacturing environment and likely to be foreign objects. In addition, the technique provides an advancement in the quantification of foreign objects with an average error in determining the area of foreign objects of 2.5% in one study presented. The final contribution of this work is the presentation of a portable ultrasonic housing that allows for the acquisition of ultrasound scans with comparable resolution to those taken from an immersion system. Foreign object detection and quantification is demonstrated using this housing and compared with scans taken from an immersion system. The housing allows for additional real-world applications of the developed techniques presented in this dissertation.