NDT technologies for ceramic matrix composites: Oxide and nonoxide

Ceramic matrix composites are usually classified into two materials systems: oxide based and nonoxide based. Oxide based systems consist of an oxide fiber and an oxide matrix, whereas nonoxide systems can consist Of carbon fibers with a carbon matrix (C/C), carbon fibers with a silicon carbide matrix (C/SiC), as well as silicon carbide fibers with a silicon carbide matrix (SiC/SiC). In addition, several processing techniques affect the mechanical and thermal properties of these materials and thus affect the nondestructive testing (NDT) applications. Furthermore, most of these materials utilize an environmental barrier coating that protects the base material. This added layer also complicates the NDT applications. NDT technologies have been developed for characterizing these advanced material systems during manufacture so that process improvements can be assessed and health monitored during service. Also, initial work has been done to estimate remaining useful life. NDT technologies that have been demonstrated to be applicable include thermal imaging that uses high frame rate, focal plane array infrared imagers with special software; air coupled ultrasonics in through transmission mode; X-ray computed tomographic imaging with large area, small pixel size detectors; guided plate waves; and impact excitation resonance to measure internal friction. This paper discusses these NDT technologies and the protocols to be used for these materials.