Test methods for thin carbon-carbon composite laminates

The Solar Probe spacecraft, currently underdevelopment by the Johns Hopkins University Applied Physics Laboratory (JHU/APL), will include a large 2.7 m diameter by 5.1 m long carbon-carbon (C/C) conical Thermal Protection System (TPS) which protects the spacecraft bus and instruments during the solar encounter. Operational temperatures of up to 1600 degrees C along with system thermal, mass, and stiffness requirements dictate that the TPS structure be fabricated from a high modulus C/C composite material. A development program was conducted by JHU/APL to measure the physical and mechanical properties of candidate C/C materials for application to the TPS. Though standardized methods for testing C/C do not exist, American Society for Testing and Materials (ASTM) methods for advanced ceramics, plastics and composite materials have guided successful testing of similar but thicker C/C materials. Since the carbonization process is thickness dependent, it was critical that test coupons be of the same thickness as those of the actual structure. Special test configurations had to be developed to properly measure the properties of these thin laminates.