An efficient reliability technique is developed based on Response Surface Methodology (RSM) in conjunction with the First Order Second Moment (FOSM) reliability method. The technique is applied when the limit state function cannot be obtained explicitly in terms of the design variables, i.e. when the analysis is performed using Finite Element Codes. When compared with exact analysis, results have shown an excellent agreement. Therefore, this technique allows the extension of most Finite Element Codes to account for probabilistic analysis, where statistical variations can be added to the design variables.
An explicit solution for rocket motors consisting of propellant and steel case under environmental temperature variations is compared to the RSM technique. The method is then used for the analysis of rocket motors subjected to two opposite line loads for which the stress analysis is performed using finite element method. Results have shown that the reliability of the motor decreases as the applied load increases or the storage time increases.