Thermal imaging measurement and correlation of thermal diffusivity in continuous fiber ceramic composites

Abstract

Continuous fiber ceramic matrix composites (CFCCs) are currently being developed for a variety of high-temperature applications, including use in advanced heat engines. For such composites, knowledge of porosity distribution and presence of defects is important for optimizing mechanical and thermal behavior of the components. The assessment of porosity and its distribution is also necessary during composite processing to ensure component unifo4ty. To determine the thermal properties of CFCC materials, and particularly for detecting defects and nonuniformities, we have developed an infrared thermal imaging method to provide a "single-shot'' full-field measurement of thermal diffusivity distributions in large components. This method requires that the back surface of a specimen receives a thermal pulse of short duration and that the temperature of the front surface is monitored as a function of time. The system has been used to measure thermal diffusivities of several CFCC materials with known porosity or density values, including SYT.,RAMICm SiC/SiNC composite samples from Dow Corning and SiUSiC and enhanced SiC/SiC samples from DuPont Lanxide Composites, to determine the relationship of thermal diffusivity to component porosity or density.

Front-Flash Thermal Imaging Characterization of Continuous Fiber Ceramic Composites

“…The results showed that both plates were relatively homogeneous, with a thermal diffusivity of 0.97 mm2/s for the DCC specimen and 2.8 mm2/s for the DLC specimen. These values are consistent with those obtained for similar materials by Sun et al (1997 Fig. 7.…”

Fracture Behavior of a Si3N4-BN Fibrous Monolith Ceramic

“…The thermal imaging apparatus is comprised of a flash lamp system, an infrared camera, and a computer for data acquisition and processing. More information on this system can be found elsewhere 38 . The flash lamp system uses two standard photographic xenon flash-lamps to generate the thermal pulse.…”

Nondestructive Evaluation of Defects and Operating Damage in CFCC Combustor Liners

“…The NDE data were presented as thermal diffusivity and ultrasonic transmission (UT) images mapping the entire liners (100% inspection). The data indicated that thermal diffusivity was affected slightly by local thickness variations, as an average thickness was used for each liner to derive the local thermal diffusivity (Sun et al, 1999). The outer liner was found to be generally uniform and free of defects from both thermal diffusivity and air UT tests.…”

“…To determine their condition and assess operating damage, the liners were subjected to NDE at Argonne National Laboratory (ANL) during various processing stages, as well as before and after the engine test. The NDE techniques included pulsed infrared thermal imaging, aircoupled ultrasonic scanning, and X-ray CT (Sun et al, 1998(Sun et al, , 1999Sun, 2001). This paper presents the NDE results for the CFCC liners before and after the EBC application and after the engine test.…”