“Development of a Simplified Procedure for Rocket Engine Thrust Chamber Life Prediction with Creep”
M. L. Badlani, B. Kasraie, J. S. Porowski, W. J. O’Donnell, and D. B. Peterson, NASA Report CR-165585, October, 1981.
Keywords: rocket thrust chamber; hot-gas-wall ligaments; cyclic thermal strain; strain-controlled cycling; creep-enhanced ratcheting
An analytical method for predicting rocket thrust chamber life is developed. The method accounts for high pressure differentials and time-dependent creep effects both of which are significant in limiting the useful life of the shuttle main thrust chamber. The hot-gas-wall ligaments connecting adjacent cooling channel ribs and separating the coolant flow from the combustion gas are subjected to a high pressure induced primary stress superimposed on an alternating cyclic thermal strain field. The pressure load combined with strain-controlled cycling produces creep ratcheting and consequent bulging and thinning of these ligaments.
This method of creep-enhanced ratcheting is analyzed for determining the hot-gas-wall deformation and accumulated strain. results are confirmed by inelastic finite element analysis. Fatigue and creep rupture damage as well as plastic tensile instability are evaluated as potential failure modes. It is demonstrated for the NARloy Z cases analyzed that when pressure differentials across the ligament are high, creep rupture damage is often the primary failure mode for the cycle times considered.
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