Virtually all NASA spacecraft use composite overwrapped pressure vessels (COPVs) to reduce the weight disadvantage of metal pressure vessels. However, these composite structures are more susceptible to damage than metal PVs, are difficult to inspect, have large burst pressure variability, and are susceptible to stress rupture when maintained at pressure. Over the past few years, NASA's Johnson Space Center (JSC) White Sands Test Facility (WSTF) has developed novel analysis methods that show promise for assessing the structural health of composite overwrapped pressure vessels. These methods and industry standard methods have been integrated into specialized software for automated analysis, thus significantly increasing throughput to the point where real-time assessments of structural health may be determined. Adaptive analysis methods have also been developed to provide modal analyses at specified points in a structure's life, including loading, unloading, and dwells. Together, these enhancements increase the utility and ease of use for acoustic emission testing.
Supporting the development of smart structures, including the “Smart COPV” project, this software is being phased through its current post-test analysis function into an in-situ structural health monitoring (SHM) tool. In simple terms, the adaptation transforms the technology from a difficult-to-understand measurement into the equivalent of a “check engine” light for a structure. If hazardous conditions are identified, crew will be alerted with instructions. Data may then be streamed to NASA JSC WSTF via the Tracking and Data Relay Satellite System (TDRSS) ground terminal adjacent to the facility for expert evaluation. If imminently hazardous conditions exist, the system may be configured to relieve a small amount of pressure for hazard mitigation.
Adaptive methods allow the software to analyze data per standard and proprietary methods automatically with little initial tuning. Pressure profiles are composed of load, unload, and dwell segments. This feature allows the software to perform segment-dependent modal acoustic emission analysis techniques automatically. Additionally, burst pressures may be predicted with good accuracy using proprietary methods developed at WSTF. Data from representative COPVs and tensile specimens were analyzed, producing trends that are advantageous to project burst pressures that are unique to each test article evaluated.
This work was done by Regor L. Saulsberry, Charles Nichols, Douglas Weathers, Jonathan M. Tylka, Kenneth L. Johnson, and Donald J. Roth of Johnson Space Center; and Jess M. Waller and Joshua Simmons of Jacobs Technology Inc. This software is available for use. To request a copy, please visit here.