A Constitutive Model For Modified Double-base Propellant Over A Wide Range Of Strain Rates And Temperatures And Its Application

With the development of higher tactical and technical performance of solid rocket weapon system,the solid rocket motor develops towards higher loading density,thicker propellant web,lager length-diameter ratio,and higher particle content propellant grain.Due to the rocket extended-range projectile and gun-launched missile come into sevice and ejecting launch technique is widely used,the solid propellant grain's structure integrity problem under impact loadings becomes more and more important.During the process of manufacturing,transportation and storage,the temperature of solid propellant is differring from-50? to +60?,so it is improtant for grain's structure integrity to take the temperature and strain rate effect into the mechenical propeties of the solid propellant.This theis is focused on the mechanical propeties of a modified double-base propellant,and the research work is summarized as follows:(1)The dynamic mechanical analysis of the modified double-base propellant was carried out under the alternating loadings with the temperautre range of-100??+100?,the mechnical propeties of the modified double-base propellant under three different states,glassy state,viscoelastic stae,and rubbery state,were studied.The relaxtion transition temperature and instantaneous modulus are determined as frequency-dependent function relationship,and the storage modulus model of the modified double-base propellant under wide temperature range was developed,which could accurately characterise the storage modulus of the modified double-base propellant under glassy state,viscoelastic stae,and rubbery state.(2)the quasi-static compressive experiments for the modified double-base propellant were carried out over-40? to 60?m using material testing machine,and the stress-strain curves at low strain rates,1.1×10-4s-1?5.5×10-1S-1,were obtained.The experimental results show that the failure of the modified double-base propellant was related to maximum shear stress failure criteria,The the stress-strain curves were dependent on temperature and strain rate,and the initial elastic modulus and yield stress increased with either increasing the strain rate or decreasing temperature.There is a particular transition strain rate at the specific temperature,if the strain rate was less than the particular transition strain rate,strain harden effect is observed in stress-strain curves after yielding,if the strain rate is greater than the particular transition strain rate,the stress drop effect is observed in the stress-strain curve after yielding,which was related to the process of damage accumulated and developed.Compared with the mechnical properties of a double-base propellant,the filled RDX particle reduces the mechanical properties of the modified double-base propellant.(3)The mechnical properties under impact loading for modified double-base propellant are studied over-40? to 40?,using SHPB setup,and the stress-strain curves at high strain rates are obtained.The experimental results show that the mechanical properties under impact loading were strongle dependent on temperature and strain rate,and the initial elastic modulus and yield stress increased with either increasing the strain rate or decreasing temperature,what's more,they increase substantially at high strain rates compared with those at quasi static.Compared with the mechnical properties of PC and a double-base propellant,the mechanical properties shortcoming of modified double-base propellant under impact loading is that the stress drops after yielding and unable to deform lagerly,(4)The viscoelastic-ideal plastic constitutive model was proposed for modified double-base propellant under a wide range of strain rate and temperature.The viscoelastic model consists of strain rate-temperature dependent Maxwell component and temperature dependent spring in parallel,in which the initial elastic modulus and the relaxation time of Maxwell component are dependent on strain rate and temperature,and the elastic modulus is nonlinear relationed to the temperature.The Richeton cooperative thermally activated model was modified by developing the internal stress model and the activated energy model,which can give satisfactory results for yield stress of modified double-base propellant over a wide range of strain rates and temperatures.(5)The numeric implementation of the developed constitutive model and simulation for modified double-base propellant are done.The 3-D constitutive model for modified double-base propellant is derived based on isotropy assumption,and the incremental form of 3-D constitutive model is obtained.The VUMAT subroutine is programmed for ABAQUS software,and the static and dynamic simulations are carried out to verify VUMAT subroutine.The finite element model for modified double-base propellant free loading six-point star grain is established,and the structure integrity under fire pressure impact loading is simulated.This thesis is focused on the experimental researches for modified double-base propellant over over a wide range of strain rates and temperatures,and the theoretical model is proposed,which is successfully used in numerical implementation and will support solid rocket motor grain structure integrity analysis.