We developed an analytical procedure for predicting thrust chamber life on the Space Shuttle Main Engine limited by the small number of firings.
In an operating rocket thrust chamber the hot-gas-wall ligaments separating the coolant and combustion gas are subjected to pressure loading and severe thermal cycling. The resulting stresses cause plastic straining resulting in incremental bulging of the ligaments during each firing cycle. This mechanism of creep ratcheting was analyzed considering combined bending and membrane loading.
The incremental permanent deflection and progressive thinning near the center of the ligaments was evaluated. Creep and tensile instability were identified as the limiting mode of failure. Results of these analyses compared favorably with available experimental data and allowed design changes which extended the design life.