Role of the material constitutive model in simulating the reusable launch vehicle thrust cell liner response

The reusable launch vehicle thrust cell liner, or thrust chamber, is a critical component of the space shuttle main engine. It is designed to operate in some of the most severe conditions seen in engineering practice. These conditions give rise to characteristic deformations of the cooling channel wall exposed to high thermal gradients and a coolant-induced pressure differential, characterized by the wall's bulging and thinning, which ultimately lead to experimentally observed "dog-house" failure modes. In this paper, these deformations are modeled using the cylindrical version of the higher-order theory for functionally graded materials in conjunction with two inelastic constitutive models for the liner's constituents, namely Robinson's unified viscoplasticity theory and the power-law creep model. Comparison of the results based on these two constitutive models under cyclic thermomechanical loading demonstrates that, for the employed constitutive model parameters, the power-law creep model predicts more precisely the experimentally observed deformation leading to the "dog-house" failure mode for multiple short cycles, while also providing much improved computational efficiency. The differences in the two models' predictions are rooted in the differences in the short-term creep and relaxation responses.