NDE of Structural and Functional Carbon‐Carbon Composites after First Carbonization

In the processing cycle of carbon-carbon (C/C) composites, transition of the precursor polymer matrix to a carbon matrix takes place at the stage of first carbonization. Matrix microcracking, interfacial debonding, and development of distributed porosity are some consequences of first carbonization. A key to assessing and optimizing these properties of the final material is to successfully define nondestructive evaluation (NDE) microstructure-process relationships for different material precursor systems at the stage of first carbonization. Here such a study is undertaken through a systematic consideration of structural and functional fiber reinforced phenolic matrix precursor material systems. Structural composite precursor systems consisted of woven fabric architectures, such as plain, satin, and stretch broken, while the functional systems included nonwoven thermal bonded carbon fiber. These materials were subjected to ultrasonic, acoustic, and vibration NDE at their polymer and carbonized matrix stages. NDE parameters from these methods were studied in light of various mechanisms ensuing first carbonization