Pressure cure of solid propellant charge based on thermo-chemo-mechanical fully coupled viscoelastic model

Pressure cure can reduce the cure residual stress (CRS) of solid propellant charges, thereby enhancing the structural integrity and storage life. As the polymerization reaction progresses, it is accompanied by heat release, chemical volume shrinkage, and viscoelastic evolution. In this study, a thermodynamically consistent, fully coupled thermo-chemo-mechanical viscoelastic model is developed. Relaxation tests are carried out on hydroxylated polybutadiene (HTPB) propellant specimens at different cure times revel the viscoelastic evolution mechanism. Consequently, a viscoelastic evolution model is established in relation to the degree of cure (DOC). On the basis, the CRS analysis of the pressure cure HTPB solid propellant charge is performed by means of user material subroutines. The model is validated against literature and experimental results. Furthermore, factors affecting temperature, DOC and CRS are analyzed. Results indicate that the shift factor of HTPB propellant is independent of DOC, while relaxation time first increases and then decreases. Employing the multi-physics coupled viscoelastic model provides a detailed description of the CRS development. An enhanced pressure cure scheme is proposed, which involves releasing partial pressure during cure to future reduce CRS. This model establishes a foundation for designing cure cycles and predicting CRS in solid propellant charges.