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Bayes Analysis and Reliability Implications of Stress-Rupture Testing a Kevlar/Epoxy COPV using Temperature and Pressure AccelerationComposite Overwrapped Pressure Vessel (COPVs) that have survived a long service time under pressure generally must be recertified before service is extended. Sometimes lifetime testing is performed on an actual COPV in service in an effort to validate the reliability model that is the basis for certifying the continued flight worthiness of its sisters. Currently, testing of such a Kevlar49(registered TradeMark)/epoxy COPV is nearing completion. The present paper focuses on a Bayesian statistical approach to analyze the possible failure time results of this test and to assess the implications in choosing between possible model parameter values that in the past have had significant uncertainty. The key uncertain parameters in this case are the actual fiber stress ratio at operating pressure, and the Weibull shape parameter for lifetime; the former has been uncertain due to ambiguities in interpreting the original and a duplicate burst test. The latter has been uncertain due to major differences between COPVs in the data base and the actual COPVs in service. Any information obtained that clarifies and eliminates uncertainty in these parameters will have a major effect on the predicted reliability of the service COPVs going forward. The key result is that the longer the vessel survives, the more likely the more optimistic stress ratio is correct. At the time of writing, the resulting effect on predicted future reliability is dramatic, increasing it by about one nine , that is, reducing the probability of failure by an order of magnitude. However, testing one vessel does not change the uncertainty on the Weibull shape parameter for lifetime since testing several would be necessary.
Document ID
20090016744
Acquisition Source
Johnson Space Center
Document Type
Preprint (Draft being sent to journal)
Authors
Phoenix, S. Leigh (Cornell Univ. Ithaca, NY, United States)
Kezirian, Michael T. (Boeing Co. Houston, TX, United States)
Murthy, Pappu L. N. (NASA Glenn Research Center Cleveland, OH, United States)
Date Acquired
August 24, 2013
Publication Date
January 1, 2009
Subject Category
Composite Materials
Report/Patent Number
JSC-18131
Meeting Information
Meeting: 50th AIAA/ASME/ASCE/AHS/ASC Structures Conference
Location: Palm Springs, CA
Country: United States
Start Date: May 4, 2009
End Date: May 7, 2009
Sponsors: American Helicopter Society, Inc., American Society of Civil Engineers, American Society of Mechanical Engineers, American Inst. of Aeronautics and Astronautics, American Society for Composites
Funding Number(s)
CONTRACT_GRANT: USA-60000132079
Distribution Limits
Public
Copyright
Public Use Permitted.

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