关键词: NEPE固体推进剂, 加压固化, 液–固相变, 等静压传压, 残余应力

Abstract: To address the difficulty of consistently describing the liquid–solid phase transition, isostatic pressure transmission, and residual stress evolution during the pressurized curing of NEPE solid propellants, a sequentially coupled numerical simulation method driven by the curing degree is proposed. The curing degree α is employed as the phase-state variable, and the gel point αgel is introduced as the criterion for the liquid–solid transition. When α＜αgel , a liquid-phase isostatic pressure transmission model is adopted to characterize the compressive response of the propellant. Once α≥αgel , the constitutive model switches to a solid-phase formulation, and the accumulation of residual stress and strain begins. The curing reaction kinetics, exothermic heat release, and heat transfer processes are solved through thermo–chemical coupling analysis to obtain the temperature and curing-degree fields. These fields are subsequently transferred to the mechanical analysis within a sequential coupling framework to govern material state determination and the evolution of mechanical properties. User-defined subroutines are employed to realize the multi-physics-field simulation under liquid–solid phase transition conditions. The proposed framework enables a systematic simulation of pressure-induced deformation and residual stress evolution throughout the entire process, including pressurization, curing, cooling, and depressurization of the motor. The numerical results indicate that during the liquid-phase stage, the propellant primarily transmits the external load in the form of hydrostatic pressure, without generating residual stress. Upon entering the solid phase, the increasing curing degree leads to the formation of a crosslinked network structure, transforming the propellant into a solid state. Meanwhile, the elastic rebound of the motor case compensates for the volumetric shrinkage induced by curing and cooling. The proposed pressurized curing simulation method provides a more physically consistent description of the timing of case rebound and its influence on residual stress relaxation. Compared with conventional simulation approaches, the maximum residual stress and strain are reduced by 17.05% and 20.83%, respectively. These results provide a reliable numerical tool for optimizing the pressurized curing process and controlling residual stresses in NEPE propellant grains.

Key words: NEPE solid propellant, pressurized curing, liquid–solid phase transition, isostatic pressure transmission, residual stress