Life evaluation of a combustion chamber by thermomechanical fatigue panel tests based on a creep fatigue and ductile damage model

The inner liner of a combustion chamber of a cryogenic liquid rocket engine is exposed to a high load induced by the high temperature of the hot gas and the low temperature of the coolant. The high load causes some inelastic strain that accumulates with each operational cycle until the fracture or rupture of the inner liner. A model that can reproduce the propagation of damage under a thermally cycled load is essential for precisely predicting the chamber life. However, the damage propagation phenomenon or the quantitative value of the damage was so far not fully discussed using the damage data obtained from basic testing of a rocket chamber material. The purpose of the present study was to investigate a precise prediction model based on damage mechanics for simulating the damage propagation of a rocket chamber material. In this study, low cycle fatigue test data at a high temperature (900 K) were analyzed, and damage models that could reproduce the damage propagation under cyclic load conditions were investigated. Then the parameters were identified to reproduce uniaxial test data. These damage models were also subject to a finite element method analysis of a thermomechanical fatigue panel test in order to quantitatively evaluate the deformation, damage propagation, and life of a chamber wall. The analysis of low cycle fatigue test data at 900 K suggested a specific model that could precisely reproduce the damage propagation phenomenon and the basic material test data. From the results, it was confirmed that the model could predict the location of crack initiation.