Viscoelastic Constitutive Model And Its Application To Composite Solid Propellant In Pressure Cure Stage

Pressure cure molding technology is one of the key technologies of the new generation of high load solid rocket motor.The analysis of residual stress of the propellant string during pressure cure is the bottleneck restricting the development of this technology,and its core problem is the lack of effective integrated constitutive model of fluid-solid transition.This paper carries out a special study on this problem and applies it to temperature and pressure path optimization in pressure cure process.The main work is as follows:The elastic-viscoelastic segmented splicing constitutive model and the curingcooling integrated viscoelastic constitutive model related to the degree of cure are proposed,which solves the problem that the residual stress in the curing process and the cooling process of the grain cannot be calculated uniformly.The degree of cure was introduced,and based on the linear elastic model of the resin cure constitutive model,the linear elastic constitutive model of the propellant in the curing stage was established.Combined with the typical viscoelastic constitutive model of the cooling stage,the elasticviscoelastic segmented splicing constitutive model related to the degree of cure is obtained.Considering the viscoelastic properties of the propellant during the curing process,based on the generalized Maxwell model,a curing-cooling integrated viscoelastic constitutive model related to the degree of cure is established.This model realizes the continuous transition of propellant from viscous fluid to viscoelastic solid.The constitutive model is compared with the experimental data in the literature,which verifies the validity of the constitutive model.Based on the incremental finite element method,the incremental form of the constitutive model and the uniform tangent stiffness matrix is derived,and the ABAQUS software is embedded to realize the three-dimensional finite element analysis of the typical solid motor structure pressure cure process.The elasticviscoelastic segmented splicing constitutive model related to degree of cure and the curing-cooling integrated viscoelastic constitutive model related to degree of cure are respectively numerically discretized,and the Jacobian matrix is derived.Through the UMAT interface of ABAQUS software,the secondary development of two subroutines for cure constitutive models has been completed.A finite element model of a typical solid motor was established,and two cure constitutive models were used to carry out a fullprocess pressure cure simulation,and the simulation results of different constitutive models are compared.The simulation results conform to the actual law of the pressure cure process.The optimal path model of pressure-curing temperature-pressure with the goal of minimizing residual stress was established.The joint optimization method of ISIGHT and ABAQUS was proposed,and the theoretical pressure of pressurecuring and the optimal rate of pressure relief and temperature reduction were studied.Taking the minimum residual stress of the propellant grains after pressure cure as the optimization goal,using the Evol evolutionary algorithm in ISIGHT software,combined with the curing-cooling integrated viscoelastic constitutive model related to the degree of cure,the load parameters during the pressure cure process(The pressurization pressure value,pressure relief rate and temperature drop rate,etc.)have been optimized.It is confirmed that the pressure value is positively correlated with the effect of reducing residual stress and strain,provided that the pressure value does not exceed the theoretical pressure required for pressure cure.When the attenuation coefficient of the pressure relief curve is 7300 and the attenuation coefficient of the temperature drop curve is 9550,the stress and strain extremes during the pressure cure process are the smallest.In the end,the optimal pressure cure plan was obtained.The research results of this paper provide a model basis for the basic research of solid propellant pressure cure,and provide a technical method for the fine pressure cure analysis of solid rocket motors.