Influence of mechanical hardening and numerical setup on liquid rocket engine combustion chamber life perdition

The thrust chamber of high-performance bipropellant liquid rocket engines is a critical component in reusable launch vehicles, as it directly influences engine efficiency, structural integrity, and operational lifespan. To withstand the extreme thermal and mechanical loads experienced during operation, these chambers employ a regenerative cooling system, which serves a dual purpose: it mitigates the severe thermal stresses on the chamber walls by dissipating heat while simultaneously preheating the fuel or oxidizer before injection, enhancing overall propulsion efficiency. Ensuring the durability and reusability of thrust chambers necessitates accurate thermo-mechanical life prediction. However, estimating their operational lifespan is challenging due to several factors, including the lack of reliable simplified specimen characterization, uncertainties in heat flux prediction, and the difficulty in selecting an appropriate plasticity model for computational analysis. These challenges often lead to an overestimation of service life, necessitating extensive and costly test campaigns until structural failure. Such experimental validation remains essential for refining numerical thermo-mechanical models and improving predictive capabilities. This study aims to investigate the influence of numerical modeling assumptions on the life prediction of copper-based liquid rocket engine combustion chambers using a commercial structural finite element method (FEM) solver. Specifically, a comparative analysis is conducted between different modeling approaches, including 2D plane strain, 2D generalized plane strain, and 3D generalized plane strain formulations. These approaches are evaluated in conjunction with a second-order Chaboche-Voce hardening model, incorporating both kinematic and isotropic hardening effects. The study places particular emphasis on the impact of low-cycle fatigue and ratcheting damage, which are critical failure mechanisms in cyclic thermal loading conditions. To validate the numerical models, experimental data from the Space Shuttle Main Engine (SSME) sub-scale cylindrical thrust chamber test campaign at NASA’s former Lewis Research Center (LeRC) are used as a reference case study. The LeRC plug thrust chambers provide a unique opportunity for hardware-representative low-cycle thermal fatigue evaluation, offering essential benchmark data, including precise temperature measurements obtained from multiple-depth intrusive thermocouples and recorded cycle-to-failure counts. By leveraging this rare experimental dataset, the study aims to establish validated thermal boundary conditions and enhance the predictive accuracy of thermo-mechanical analyses for reusable liquid rocket engine thrust chambers.