Inspection on SiC coated carbon-carbon composite with subsurface defects using pulsed thermography

An investigation on SiC coated carbon-carbon (C/C) composite plates has been undertaken by pulsed thermography. The heat transfer model has been built and the finite element method (FEM) is applied to solve the thermal model. The simulation results show that defects with DA/DP smaller than one can hardly be detected by an infrared camera with the sensitivity of 0.02 C. Certificated experiments were performed on the built pulsed thermography system. The thermal wave signals have been processed by subtracting background image method (SBIM), pulsed phase thermography (PPT), and temperature-time logarithm fitting method (TtLFM). The limit DA/DP of defects in SiC coated C/C composite plates with the thickness of 6 mm that can be detected by pulsed thermography with the presented signal analysis algorithms has been obtained.