Cyclic Stress Analysis of a Rocket Engine Thrust Chamber Using Chaboche, Voce and Creep Constitutive Models

Abstract

High thrust rockets require high performance liquid engines for its propulsion. The thrust necessary for propulsion is produced by mixing, burning and ejecting a fuel and an oxidizer inside the thrust chamber of the engine. The engine investigated in this study is an indigenously developed semi-cryogenic engine developing a thrust of 2000 kN in vacuum. Its thrust chamber is of double walled construction, with inner wall of an indigenously developed high conductivity high ductility copper alloy and outer wall of high strength stainless steel. The inner wall operates in the elasto plastic condition due to high thermal and pressure loads. Structural failure of the chamber occurs due to repeated hot tests of the engine by low cycle fatigue (LCF), high temperature creep and thermal ratcheting of inner wall. In this paper, cyclic stress analysis of the thrust chamber is done using ANSYS (Version 16) code. A combination of Chaboche nonlinear kinematic hardening plasticity model, Voce nonlinear isotropic hardening model and Norton secondary creep model is used for copper, while bi-linear kinematic hardening model is selected for stainless steel. Steps for calibration of Chaboche and Voce model parameters from tensile and LCF tests are given in detail while published creep properties are used directly in the analysis. Stress analysis of chamber is done for 25 cycles and permissible number of hot tests evaluated based on Coffin–Manson type LCF equation.