NASA LogoNTRSNTRS - NASA Technical Reports ServerSearchmore_vertCollectionsAboutNewsHelpLogin Back to ResultsPreload Loss in a Spacecraft Fastener via Vibration-Induced UnwindingSound engineering practice requires that fasteners and bolted joints maintain preload in service. NASA recently concluded a series of vibration tests of a multicomponent structure intended to simulate an upper stage section of a launch vehicle. The stacked components were joined through six circumferentially placed bolted cup-cone-style pyrotechnic joint mechanisms designed to share spacecraft structural loads and then enable separation during ascent. Over the course of the vibration test campaign, all six bolted cup-cone mechanisms experienced some degree of preload loss with two mechanisms losing half of their original bolt preload. A subsequent forensic anomaly investigation concluded that vibration-induced unwinding of the preload nut-and-bolt assemblies occurred despite the use of safety wire and high levels of thread friction. A series of experiments were done to better understand how large, heavily preloaded fasteners could unwind. Additionally, thread friction torque was measured and the fastener locking capability of safety wire was evaluated. The friction coefficient between the clamped cup-cone components was characterized and finally a highly instrumented mechanism-level vibration test was done to reproduce the unwinding phenomenon to better understand the mechanism's behavior. The conclusion drawn was that vibration and structural forces led to relative motion (sliding) of the clamped components, resulting in self-loosening and unwinding effects on the nut-and-bolt assembly. To counter this phenomenon, more effective fastener locking methodologies were recommended and a follow-on effort was initiated to quantify the relationship between preload, component motion, and resulting unwinding forces. It is hoped that elucidation of these effects can be used to design more effective fastener locking features.Document ID20180002978Acquisition SourceGlenn Research CenterDocument TypeTechnical Publication (TP)AuthorsDellaCorte, Christopher*(NASA Glenn Research Center Cleveland, OH, United States)*Howard, S. Adam*(NASA Glenn Research Center Cleveland, OH, United States)*Hess, Daniel P.*(University of South Florida Tampa, FL, United States)*Date AcquiredMay 21, 2018Publication DateApril 1, 2018Subject CategorySpacecraft Design, Testing And PerformanceReport/Patent NumberGRC-E-DAA-TN51642E-19490NASA/TP-2018-219787Funding Number(s)CONTRACT_GRANT: NNL12AA09WBS: WBS 747797.06.13.06.20.03Distribution LimitsPublicCopyrightPublic Use Permitted.KeywordsfastenersmechanismsvibrationAvailable DownloadsNameType20180002978.pdfSTIcloud_downloadcontent_copyvisibilityRelated RecordsThere are no records associated with this record.visibility_offNo Preview Available
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