Reliability analysis and quality assurance of rocket motor case considering proof testing

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Reliability analysis and quality assurance of rocket motor case considering proof testing

Yang, J.N. / Chen, H.Y. / Chang, C.M. / Shee, H.K.

Proof testing has been used extensively in industry for quality assurance of some types of structural components, such as pressure vessels, rocket motor cases, etc. It has also been used as an alternative means of maintenance for structural components in which the critical locations are not accessible for inspection maintenance. In this paper, the effect of proof testing on structural reliability in service is investigated. Emphasis is placed on practical applications of the reliability theory to the quality assurance of rocket motor cases. Multiple failure modes, including fracture failure, plastic yielding collapse and their interactions, are considered. All the physical quantities, such as the fracture toughness, yield stress, flaw length, flaw geometry, service loads, geometric dimensions, etc., are considered as statistical variables. It is demonstrated that proof testing is most effective when the statistical variability of the service load is small or the statistical dispersion of the overall strength of the structure is large. Proof testing is shown to be ineffective if the variability of the overall structural strength is small or the dispersion of the service load is large. In the latter case, the effectiveness of proof testing can be enhanced by increasing the design safety actor.