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Viton B O-Ring Resilience Study

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The Challenger accident in January 1986 was attributed to failure of the pressure seal in the aft field joint of the solid rocket motor. It was concluded that the elastomeric O-ring seals did not perform their sealing function because of the low temperatures at launch. Because the Shuttle and Titan O-rings were both made of Viton, there was concern that the O-rings on the segment tang and clevis joints on the Titan solid rocket motor might cause a similar problem. Launch delays that exceeded the assembled segment O-ring service life of 12 months also raised concerns. These delays resulted in the initiation of a pad-life extension program and a reevaluation of the O-ring seal. Structural analysis of clevis joint motion had predicted that a gap could be generated at the clevis joint where the O-ring is seated. This gap must be closed by O-ring decompression to maintain the seal during ignition, pressurization, and flight This decompression determined by the resilience of the O-ring - must take place rapidly enough to seal the clevis joint in advance of increasing exhaust gas pressure. This report presents data on the resilience characteristics of Vitonregistered B O-rings under long-term compression in real time. These data can be used in conjunction with structural analysis of joint motion to predict joint seal performance during installed seal lifetime. The resilience of Vitonregistered B O-rings was measured as a function of initial 17 and 23 compression, time under compression up to 3 years, test temperatures of 60 deg F and 70 deg F, and O-ring lot. The results showed that resilience of Viton B O-rings is reduced significantly as the temperature is lowered and with increasing time under compression, which is of concern when segments are stacked for long periods of time.

Subject Categories:

  • Adhesives, Seals and Binders
  • Elastomers and Rubber

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