Numerical Simulation Of Meso-mechanics Damage In Composite Solid Propellant Based On Mesoscopic Model

With the long-range,light-weight and high-mobility requirements of rocket and missile weapon system,the composite solid propellants are widely used in engineering field.HTPB(Hydroxyl-terminated polybutadiene)propellant has become the most promising propellant due to its high volume density,high specific impulse,excellent mechanical properties and other advantages.Large amounts of solid oxidant particles and metallic fuel particles are added to improve the energy of HTPB propellant,and this is bound to change the meso-structure component of composite propellant.As the consequence,the mechanical properties of propellant are changed,which makes it more difficult to apply propellant to engineering use.Therefore,for providing guidance of propellant formula design and its application in a wider range,the macro test and numerical simulation method were used in this paper to reveal the mechanical properties of HTPB propellant and its mechanism of mesoscopic damage.The main contents of this thesis are as follows:(1)Study on mechanical properties of composite solid propellant of custom-built formulation.The mesoscopic morphology of HTPB propellant fracture surface was observed by SEM(scanning electron microscope),and the particles shape,distribution and the initial defects in HTPB propellant were analyzed.Then,the uniaxial tensile and stress relaxation test of HTPB equivalent binder films were conducted and a visco-hyperelastic constitutive model was established to describe its complicated mechanical behavior,and the model can accurately describe the uniaxial tensile mechanical response of HTPB propellant equivalent binder fiilms.Finally,mechanical test of HTPB propellant of custom formulation were carried out,it finds out that the main mechanical parameters are affected by strain rate and the propellant shows typical viscoelastic properties.The comparison between experimental curves of propellant with different formula indicate that the filling particle volume fraction of have a significantly effect on the initial modulus,tensile strength and relaxation modulus of HTPB propellant.(2)Establishment of composite solid propellant mesoscopic model and the numerical simulation analysis.Combining with the basic component parameters of HTPB propellant,the mesoscopic model was established based on molecular dynamics simulation algorithm,and then the self-defined cohesive zone model was selected to describe the mechanical response of the adhesion interface between particles and matrix.Then,the several typical stages of HTPB propellant stretch process and the corresponding mesoscopic damage and evolution process were analyzed through the finite element calculation results,and this reveals the inner mechanism of the macroscopic mechanical properties of HTPB propellant.(3)Influence of interface property on composite solid propellant mechanical properties and the inversion optimization method of parameters.First,the effect of interface stiffness,strength and failure displacement was studied by changing the parameters of cohesive zone model,and the result attests that each parameter corresponds to a phase of the stretching process.Then,to overcome the absence of the interface parameters obtaining tool,taken the interface size effect into consideration,the mechanical parameters of HTPB propellant interface at different stretching rates were determined based on the step-by-step inversion analysis method and the macroscopic mechanical test results.At last,the parameters were verified by the test results of the gradational propellant and the error is less than 16.3%.(4)Influence of structural components on mechanical properties of composite solid propellant.The influence of meso-structure on its macroscopic mechanical properties was studied,and the result shows that the macroscopic mechanical behavior of HTPB propellant is strongly dependent on its meso-structure,the volume fraction of filling particles affects HTPB propellant initial modulus while the grain size distribution determines the tensile strength and breaking elongation rate of HTPB propellant.Then the influence of initial interface defect on the tensile and stress relaxation response of HTPB propellant was analyzed,and it is found out that interface defects reduce the mechanical properties of HTPB propellant and the higher the defect content,the lower the mechanical properties.With the content of defect increasing,the initial modulus and tensile strength of the propellant show an index downward tendency,and the initial defects have no effect on stress relaxation behavior of HTPB propellant,but only make difference to quantitative value of the relaxation modulus.In this thesis,the macro mechanical properties and intrinsic mechanism of HTPB propellant were analyzed,and the influence of the meso-structure component and initial defects in HTPB propellant on its macroscopic mechanical properties were also studied through test and numerical simulation.The research result has high scientific theoretical significance and engineering application value,thus it can be used to optimize the propellant formulation design and solve the structural integrity of solid rocket motor.