Research On Visco-Elastic-Plastic Constitutive Model With Damage Of Modified Double-Base Propellant And Its Application

Solid rocket motors are widely used and subjected to a variety of external factors,including shocks,accelerations and extreme temperature changes over their entire lifespan,which making grain’s structural integrity problems become more severe.Different forms of external loads on the solid propellant grains lead to the complexity of the distribution of stress,thus different stress types exist in different regions.This poses a requirement on the stress type correlation of material constitutive models.The main jobs of this research on the mechanical properties of double-base propellants are as follows:(1)A series of tensile and compressive constant strain rate tests were carried out on the modified double-base propellants,the rate dependent mechanical response of the material was analyzed.Creep tests on modified double-base propellants under different temperatures and different stress levels were done,Time-Temperature Superposition Principle and Time-Stress Superposition Principle were discussed for modified double-base propellants,The influence of time-temperature and time-stress on the mechanical response was analyzed.The tension-compression asymmetry mechanical response under constant strain rate of modified double-base propellant was analyzed.According to the tensile and compressive creep tests of modified double-base propellants at different temperatures and different stress levels,the influence of temperature and stress on the tension-compression asymmetry of materials was analyzed.(2)The visco-elastic-plastic constitutive model with damage is established according to the mechanical response of the modified double-base propellant.The Schapery nonlinear viscoelastic constitutive model is used to describe the recoverable strain of the material,while the Perzyna viscoplastic model is used to describe the irreversible strain of the material.The damage model is introduced into the visco-elastic-plastic model by the concept of equivalent stress.By analyzing the asymmetric mechanical response under tension and compression of modified double-base propellant and researching on the internal causes of these phenomena,the asymmetric tension-compression viscoplastic constitutive model and viscodamage constitutive model were established.A criterion to determine the state of tension and compression mechanics was proposed.The test of the hollow disc structure and the finite element simulation calculation on it show that it is very important to choose the appropriate constitutive model according to the mechanical state of the material.(3)Based on the characteristics of the one-dimensional visco-elastic-plastic constitutive model with damage of modified double-base propellant,the numerical solution of strain response of the model under constant stress and constant stress rate loading-unloading conditions was obtained by backward Euler method combining with Newton iteration method.Irn order to obtain the model parameters,the viscoelastic,viscoplastic and viscodamage response of the material are separated by controlling the stress level and loading time of creep-recovery response.Viscoelastic model parameters were obtained by using the least squares method.Optimized viscoplastic parameters and viscodamage parameters were obtained by using the improved simplex optimization algorithm combined with the numerical solution of one-dimensional constitutive model.Creep-recovery tests and constant loading-rate-recovery tests are done to verify the model.(4)The visco-elastic-plastic constitutive model with damage of modified double-base propellant was derived in incremental form,and was compiled into the user-defined material(UMAT)subroutine provided by ABAQUS.The simulation results under creep-recovery load were compared with tests as well as numerical solution of one-dimensional constitutive model,which verified the UMAT subroutine.(5)The finite element model for modified double-base propellant free loading six-point star grain is established,and the structure integrity under ignition pressure load and acceleration overload are simulated based on the visco-elastic-plastic constitutive model with damage and tension-compression asymmetry of modified double-base propellant.In this paper,based on the tensile and compressive mechanical response of modified double-base propellant,the visco-elastic-plastic constitutive model with damage and tension-compression asymmetry was established,and the finite element simulation of the model was realized to provide some guidance to grain design of solid rocket.