Study On A Constitutive Model Of Solid Propellant Considering Viscoelastic Poisson's Ratio And Its Implementation

Determination of the Poisson's ration of solid propellant is one of the hard problems which puzzle the researchers who study on the structural integrity assessment of solid rocket motor(SRM).The structural integrity assessment of SRM is another hard problem for the long serving time and complex loading case.The establishment of the reasonable mechanical model based on the complex mechanical parameters and the accurate description of the strain and stress response of the grains based on the model are the important research projects.The main point of the research are the determination of the viscoelastic Poisson's ration,aging development and the nonlinear viscoelastic constitutive model considering the viscoelastic Poisson's ratio and its implementation.Main achievements summarized as followsThe method of accurate measurement of the viscoelastic Poisson's ration considering time and temperature is proposed based on the digital image correlation method.The definition of viscoelastic Poisson's ration under the relaxation test is deduced based on the elastic-viscoelastic corresponding principle.The viscoelastic Poisson's ration measurement system is built considering time and temperature.The viscoelastic Poisson's ration is determined under different temperatures through the system.The variation of the Poisson's ration under different temperatures is analyzed and will lay the foundation for the establishment of the viscoelastic Poisson's ration master curve.Furthermore,the effects of the longitudinal strain,preload on the Poisson's ration are analyzed through the system too.The measurement system established can be used by determining the Poisson's ration of other viscoelastics.An aging evolution equation of Poisson's ration is proposed based on the variation of degree of cross linking by studying on the modified aging evolution equation of relaxation model.The aging Poisson's ration and relaxation model are monitored by carrying out accelerated aging test on solid propellant.The parameters of the aging evolution equation of Poisson's ration and relaxation model are fitted by least square method.The aging evolution equation of Poisson's ration and the modified aging evolution equation of relaxation model are verified indirectly through constant speed tensile test.The aging evolution equation of Poisson's ration and relaxation model proposed can be used for further study on the aging viscoelastic constitutive model of solid propellant.The viscoelastic Poisson's ration master curve of solid propellant is established based on the time-temperature principle and WLF equation.A nonlinear viscoelastic constitutive model of solid propellant is proposed.The viscoelastic constitutive model in incremental form is deduced based on the incremental finite element method(FEM)and fully explicit integration method.The constitutive model is realized in finite element software by using the consistent tangent stiffness acquired based on the programming rules of user subroutine in MSC.Marc.The structural integrity assessment of solid propellant grains is analyzed by using viscoelastic and elastic Poisson's ration under solidification process,temperature cycling process and ignition pressurization process.Furthermore,the strain and stress response of different kind of Poisson's ration are compared.The method and result can provide a reference for the engineering application of viscoelastic Poisson's ration.The research achievement can provide theoretical foundations for further refined structural integrity assessment and analytic view for accurate life predication of SRM.The research has important theoretical value and engineering application value.