NDE OF STRUCTURAL AND FUNCTIONAL CARBON-CARBON COMPOSITES AFTER FIRSTCARBONIZATION

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 debond ing, and development of distributed porosity are some consequences of first carbonization. A key to assessing and optimizing these propertie s of the final material is to successfully define nondestructive evalu ation (NDE) microstructure-process relationships for different materia l precursor systems at the stage of first carbonization. Here such a s tudy is undertaken through a systematic consideration of structural an d functional fiber reinforced phenolic matrix precursor material syste ms. Structural composite precursor systems consisted of woven fabric a rchitectures, such as plain, satin, and stretch broken, while the func tional systems included nonwoven thermal bonded carbon fiber. These ma terials were subjected to ultrasonic, acoustic, and vibration NDE at t heir polymer and carbonized matrix stages. NDE parameters from these m ethods were studied in light of various mechanisms ensuing first carbo nization.