Dynamic Viscoelastic Constitutive Model And Its Application To Composite Solid Propellant

The dynamic loads of solid rocket motor(SRM)such as vibration and impact will influence or even destroy the structural integrity of the grain.How to accurately estimate the mechanical behaviors of composite solid propellant underwent actual working loads,establish a reasonable and accurate dynamic viscoelastic constitutive model and apply it to the structural analysis of SRM grain are the important subjects for both designers and users.In this dissertation,the composite solid propellant was taken as the research object,a nonlinear viscoelastic constitutive model considering ?dewetting? and strain rate was established,the numerical method and engineering application was studied.The main research contents are as follows:For the requirements about structural integrity analysis of the SRM grain,the mechanical property of a new hydroxyl-terminated polybutadiene propellant is studied by uniaxial tensile tests under complex loads.Constant and composite speed tensile tests were made in the high,normal and low temperature to study the effect to ultimate mechanical properties and dewetting with temperature,stretching rate,and switching strain.A rate-related nonlinear viscoelastic constitutive model of propellant considering ?dewetting? was established.The ZWT model was applied to the composite solid propellant,combining with the experimental results of mechanical properties of propellant,the dewetting behavior of propellants is simulated using the “dewetting factor”.Finally,establish a viscoelastic constitutive model of propellants considering ?dewetting? and strain rate.The constitutive model was validated by stress-strain curves obtained by other strain-rate tensile tests.The finite element method(FEM)of viscoelastic constitutive model considering ?dewetting? and strain rate was studied.The numerical method is used to discretize the constitutive equation and the incremental form is obtained.By introducing the dewetting factor,the nonlinear viscoelastic constitutive model considering strain rate and dewetting are formulated.Based on the secondary-development technology of commercial finite element software,the corresponding user subroutine of UMAT was prepared.Finally,the UMAT subroutine was verified through three-dimensional simulation analysis of the uniaxial tensile test of propellant.The effect on the structure response of the SRM grain corresponding with pressurization loading rate and ?dewetting point? elongation was studied.In order to meet the need of structural integrity analysis for SRM grain under dynamic load,a structural analysis module is developed.Based on the new viscoelastic constitutive model of propellant and the UMAT subroutine,the real ignition conditions were simulated using commercial finite element software.The effects of ignition pressurization loading rate and ?dewetting point? elongation on the structural integrity of SRM grain were studied.The work of this paper provides a technical support for dynamic structural integrity analysis of real SRM,and is of great value in theory and engineering application.