New methods for structural health monitoring are being assessed, especially in high-performance, extreme environment, safety-critical applications. One such application is for composite cryogenic fuel tanks. The work presented here attempts to characterize and investigate the feasibility of using imbedded piezoelectric sensors to detect cracks and delaminations under cryogenic and ambient conditions. A variety of damage detection methods and different sensors are employed in the different composite plate samples to aid in determining an optimal algorithm, sensor placement strategy, and type of imbedded sensor to use. Variations of frequency, impedance measurements, and pulse echoing techniques of the sensors are employed and compared. Statistical and analytic techniques are then used to determine which method is most desirable for a specific type of damage. These results are furthermore compared with previous work using externally mounted sensors. Results and optimized methods from this work can then be incorporated into a larger composite structure to validate and assess its structural health. This could prove to be important in the development and qualification of any 2nd generation reusable launch vehicle using composites as a structural element.
Marshall Space Flight Center (MSFC) has been performing optical wavefront testing at cryogenic temperatures since 1999 in the Space Optics Manufacturing Technology Center's (SOMTC's) X-ray / Cryogenic Facility (XRCF). Recently the cryogenic optical testing capability has been extended to a smaller chamber. This smaller horizontal cylindrical vacuum chamber has been outfitted with a helium-cooled liner that can be connected to the existing helium refrigeration system bringing the kilowatt of refrigeration capacity to bear on a 1 x 2 meter test envelope. Cryogenic cycles to 20 Kelvin, including set-up and chamber evacuation/backfill, are now possible in only a few days. Since activation and chamber characterization tests in September 2001, the new chamber has been used to perform a number of proprietary cryogenic tests on mirrors, adhesives, and actuators. A vibration survey has also been performed on the test chamber. Chamber specifications and performance data, vibration environment data, and optical test capability will be discussed.