Numerical Study on Residual Stress in the Forming Process of NEPE Solid Propellant

Studying the curing and forming process of NEPE solid propellants and exploring the distribution laws of their stress and strain are of great significance for the efficient production, long-term storage, safe transportation and use of NEPE solid rocket engines. In this paper, the thermal stress distribution of the propellant grain in NEPE solid rocket engines is studied by applying the small deformation linear thermoviscoelastic constitutive relationship. The stress of the viscoelastic body gradually decays over time. The relaxation modulus represented by the prong series and the WLF equation representing the time-temperature equivalence principle are obtained, and the relationship between residual stress, strain and the modulus m is discussed. The results show that the thermal stress and strain within the NEPE propellant grain are related to the magnitude of the modulus m. The residual stress increases with the increase of the modulus m. With the increase of the modulus m, the most dangerous area shifts from the connection between the two ends of the propellant grain and the insulation layer to the center of the inner hole surface. The residual strain increases with the increase of the modulus m. When the modulus m is 2, the strains of the two regions are almost equal. When evaluating the integrity of the propellant grain, both regions should be considered simultaneously. With the increase of the modulus m, the maximum residual strain of the propellant grain appears at the center of the inner hole surface. This work lays a research foundation for the subsequent selection of the integrity evaluation area of NEPE high-energy solid propellants.