Microcrack Investigation and Mitigation for Cryogenic Systems

"This program explores the entire concept of microcracking of composite materials with liquid hydrogen and liquid helium where the differential from room temperature is 500¿ or more. The program reviews microcracking on an empirical basis using resinsystems with and without fiber content. The concept of using chopped and continuous random fiber mat for preventing the penetration of microcracks through a composite material is explored using a comprehensive test program. Testing of material systems isperformed at Kirtland Air Force Base using flat panels with six-inch diameter specimens exposed to cryogenic fluid on one side with a leakage detection sensor down stream from the panel. The worst condition is a non-toughened thermoset set resin with nofiber content, which cracks rapidly and the cracks should move through the specimen with leakage recorded. This is used as the baseline test system for comparison with other resin systems. Test specimens are designed with variations in thickness andfiber content to provide a full range of empirical data. Detailed test procedures are provided. Following test, the composite specimen is mounted as a metallurgical test specimen and polished to provide measurement of microcrack and penetration. Theprincipal benefit to the government from this program will be a full, detailed exploration of the concept of microcracking when materials are exposed to a 500¿F temperature differential in the c