Numerical Simulation Study on Residual Stress and Strain in the Curing and Molding of HTPB Two-Stage Solid Propellant

Understanding the curing and molding process of HTPB two-stage solid propellants and their stress and strain distributions is essential for the efficient manufacturing, long-term storage, safe transportation, and reliable operation of solid rocket motors. In this study, the residual stress and strain generated during the curing and molding of HTPB two-stage solid propellants were numerically investigated. The mechanisms responsible for residual stress and strain were analyzed, the relaxation modulus was characterized using a Prony series and the WLF time-temperature superposition equation, and the curing and cooling processes of a two-stage solid propellant grain were simulated. Furthermore, the effects of the modulus m and length-to-diameter ratio n on the residual stress and strain fields were investigated. The results show that at the end of the curing and cooling of the grains, there are high stress and strain zones on the sides close to the core mold and the shell. At the connection point between the first-stage and second-stage grains, due to the different materials, there is a sudden change in stress and strain. The curing stage accounts for 32.1% of the total residual stress and 32.6% of the total residual strain. As the modulus m increases, the overall stress and strain of the grain increase. As the length-to-diameter ratio n increases, the overall stress and strain of the grain decrease. This work provides a basis for the dimensional design of two-stage solid propellant grains and the selection of critical regions for structural safety evaluation.