열 사이클을 겪는 고체로켓 추진제의 접착불량 신뢰성 연구

Solid rocket motor (SRM) is used in the defense and aerospace industry, because it has several advantages such as simple structure and high thrust. Since the SRM is one-shot device which is impossible to control once ignited, there is high risk of loss of the entire rocket by the small change of operating conditions or parts defect. One of such causes is the debonding of case-propellant interface which results in failure of the mission. In this study, a method is proposed that can predict reliability against the debonding of SRM propellant which undergoes thermal cycles during the long term storage. In the method, limit state function consisting of load and capacity is first formulated, which are the viscoelastic stress induced by thermal cycle and the bonding strength that degrades over time. Strength degradation is measured under isothermal condition with different temperatures by intermittent test, from which an empirical model is established as a function of temperature and time. Miner"s rule is applied to predict the strength degradation under arbitrary thermal cycle, and the result is validated by the real degradation data. Debonding stress is calculated by viscoelastic Finite element analysis(FEA) of the case and propellant interface under the thermal cycle. Finally, reliability of SRM is calculated using the concept of instantaneous and progressive reliability.