A Viscoelastic Constitutive Model of Propellant with Pressure Cure

The application of pressure cure molding technology can effectively reduce the structural integrity problems of casting solid rocket motors. In order to describe the curing and cooling process under this new technology more realistically, it is decomposed into two processes, pressurization curing, and pressure relief cooling and a time-varying segmented solid propellant intrinsic equation applicable to the pressure cure molding technology is proposed. The constitutive equation takes into account the change in material properties caused by the change in the state of the propellant during the curing process. In order to accurately model the changes in mechanical properties of the propellant during curing, the present constitutive equations for this process are rewritten in incremental form and implemented in the user subroutine UMAT of the finite element analysis platform ABAQUS. The detailed derivation steps of the constitutive equation are introduced in this paper, and the subsequent application analysis is carried out with reference to the star-shaped grain. The final stress and strain state of the propellant after cooling is used as the main analytical index. The results show that the pressure cure molding technology can effectively reduce the residual stress and the residual strain on the inner surface of the propellant grain. The pressure cure effect on the outer surface of the grain is relatively small compared to the overall reduction. The time-varying constitutive model provides technical support for a more accurate description of the pressure cure process.