Life prediction of the thrust chamber wall of a reusable rocket engine

This article presents a continuous-time structural model of the coolant channel ligament in the thrust chamber wall of a reusable rocket engine such as the Space Shuttle Main Engine. The structural analysis is based on the concepts of sandwich beam approximation and viscoplasticity, and captures the nonlinear effects of creep and plasticity interactions to represent the phenomenological effects of inelastic strain ratcheting, progressive bulging-out, and thinning in the thrust chamber wall. The damage of the thrust chamber wall is quantified as a continuous function of time in terms of the current state of ligament thinning and its critical value. The structural model has been validated for prediction of the ligament thinning by comparison with the finite element models of the thrust chamber wall structure for two different materials, namely, oxygen-free high-conductivity copper and a copper-zirconium-silver alloy called NARloy-Z. The results of parametric studies are presented to show how the service life of the thrust chamber wall is influenced by coolant channel design, ligament material, and load cycle duration. Due to its computational efficiency, this model is suitable for on-line applications of service-life prediction and damage analysis of the thrust chamber wall and also permits parametric studies for off-line synthesis of damage mitigating control systems.