Investigation On The Interfacial Mechanics Of Solid Rocket Motor Based On The Viscoelastic Cohesive Model

The main body of the combustion chamber in solid rocket motor(SRM)is made by the propellant,the insulation and the case.In macroscopic aspect,the adhesion of the propellant and the insulation will undergo a variety of harsh loads,especially in the storage stage on warships.The adhesion of SRM may let the gas enter the crack,which will lead to the failure of the ignition.In microscopic aspect,the damage effect of the "dewetting" damage caused by the failure of the adhesion between particles and the matrix will weakness the mechanical properties of the propellant,which may cause the structure integrity of the solid propellant grain to be damaged.Therefore,it is necessary to establish a reasonable macroscopic and microscopic interface mechanical model and determine the accurate model parameters by means of test method,and the simulation of mechanical behavior of the adhesion is a very important topic for engine development and use department.Taking the interface as the object,a deep investigation is conducted about the viscoelastic properties and finite element modeling systematically,structural response of the interface under different loads are analyzed,finite element model of the solid propellant in microscopic aspect considering the "dewetting" damage effect is established.The main research of this paper is as follows:The improved PPR cohesive model is established and the cohesive relationship and stiffness under different loading stages were deduced.This paper analyses the characteristics of the separation and displacement of the traditional cohesive mathematical models,and the advantages and disadvantages of the mathematical models were discussed.Considering the coupled cohesive parameters in the traditional PPR model,an improved PPR cohesive model with independent cohesive parameters is proposed.Based on the cohesive relationship in the loading stage,the improved PPR cohesive model is developed to compress,loading,unloading/reloading and damage stages.The analytical expressions of the cohesive relationship and stiffness under different loading stages are deduced.A viscoelastic cohesive model based on improved PPR model is constructed,and the acquisition of the viscoelastic cohesive parameters and the constitutive verification test are carried out.The elemental separation field is obtained based on the nodal displacements filed based on the elemental displacement transformation matrix.Based on iso-parametric element as well as the principle of virtual displacement,the elemental inner force vector and elemental stiffness matrix of the cohesive element are deduced.In this paper,the effects of the time and temperature of the viscoelastic cohesive model are studied.The acquisition and corresponding model validation of the viscoelastic cohesion parameters of the double cantilever beam with the aluminum beam,propellant,insulation,and lining layer are carried out.Two typical cohesive elements are proposed for three dimensional debonding interface in solid rocket motor,the structural analysis of the debonding interface under cooling and ignition condition is carried out.The displacement filed of the element and the derivation of the separation and displacement matrix are carried out.Based on the principle of virtual displacement,the inner force vector and stiffness matrix of the element are established,and the analysis methods of the mechanical behavior of the viscoelastic mechanics is established.The circular tube structure with prefabricated crack is studied.Cohesive elements are verified using the crack width of the top of the circular tube structure.In this paper,the structure integrity analysis of the threedimensional SRM under cooling and ignition pressure are carried out,and the distribution law of the internal traction between propellant and insulation is analyzed and summarized.The axial symmetry cohesive element is constructed,the structural analysis of the debonding interface under axial overload and wave action is carried out.By establishing reference frame,the separation and displacement matrix of the element in the reference frame is studied.Based on this,the separation field of the axisymmetric cohesive element is constructed,and the inner force vector and stiffness matrix of the element are deduced.In this paper,the relaxation test of the axial symmetrical adhesion plate is carried out,and the influence characteristics of the tensile velocity and the cohesive strength are shown in the tensile and relaxation phase.In this paper,the structure integrity analysis of the axial symmetry model of the SRM is carried out under the axial overload and the vertical rolling acceleration caused by the wave.This paper analyzes the distribution characteristics,the effects of acceleration time,temperature on the structure and the amplitude of traction which is caused by the acceleration.Finite element model of the solid propellant in microscopic aspect considering the "dewetting" damage effect is established and the mechanism of the "dewetting" damage is studied.Based on the molecular dynamics method and the two typical boundary processing methods,the finite element model of the propellant microstructure is constructed.Mechanism of the "dewetting" damage is studied by means of stretching and shear test.The analysis of "dewetting" damage based on elasticity and viscoelastic debonding interface was carried out.The effects of strain rate,volume fraction and cohesive strength on stress strain curve and "dewetting" factor were analyzed.The main object of this paper is the viscoelastic debonding interface with the known crack extension path.The research results can provide guidance for the prediction of mechanical behavior of the debonding interface in SRM.Those methods are expected to be applied in the research on the expansion of the macro and micro crack in the structure integrity analysis of the SRM.