Front flash thermal nondestructive evaluation of continuous fiber ceramic composite material

Includes bibliographical references (pages 59-60)The general purpose of the research was to advance the capabilities of nondestructive evaluation on ceramic composite materials through the development of an infrared thermal imaging technology. The research developed theoretical, numerical, and experimental methods for characterization of internal flaws in continuous fiber ceramic matrix composites (CFCC). The first part of the work consisted of optimizing an infrared thermal imaging system and improving data acquisition/analysis accuracy. The second portion of the work explored the development of a correlation between the temperature history on the sample surface and the depth and size of subsurface flaws in Carbon/Carbon and Carbon /Silicon Carbide CFCC test samples. This correlation effort began with an analytical derivation of heat diffusion through one-dimensional homogeneous plates. The analytical solutions were then used to test and optimize numerical simulation code, which in turn was used to characterize of three-dimensional flaws. The numerical simulation code was needed to study the influence of flaw characteristics (depth and size) on heat diffusion. Both numerical and experimental methods were used to determine the surface temperature-time relationship, i.e. cooling curves. Two characteristic times, the time of the peak magnitude and the time of the peak slope of the temperature difference obtained by subtracting the surface temperature over a flawed region from that over a non-flawed region, were used to detect the depth of flaws in the carbon/carbon and carbon/silicon carbide CFCC test samples. The thermal imaging system discriminated between flaws at different depths with the use of these characteristic points.M.S. (Master of Science