Mechanical Performance Prediction And Design Methods Of Composite Solid Propellant Based On VCFEM

Composite solid propellants are a kind of viscoelatic composite materials with high filling fraction.Their mechanical properties determine the structural integrity and storage life of solid rocket motor.They also affect the reliability and safety of solid missile weapons.The new missile weapons require propellants with higher mechanical properties urgently.The current design methods need to develop to satisfy these demands.Based on the Voronoi finite element method(VCFEM),the mechanical properties parameters such as the modulus and Poisson's ratio of propellants were predicted and designed in view of the microscopic scale.The main works of this thesis are summaried as follow:A method of constructing reprensentative volume element(RVE)models of propellants is proposed by combining the improved random sequential adsorption algorithm and Voronoi meshing method based on particles.The microstructure characteristics of the propellants are explored based on micro-CT images of threecomponent composite solid propellant.A random sequential adsorption algorithm is developed to construct a geometric simulation model contains widely varying size and high packing fraction particles by adopting a multi-dirction sedimentation algotithm.The rationality of the generated geometric simulation model is verified.A Voronoi meshing method considering the particle radius is proposed.This method avoids cutting particles when implements finite element discretization on the geometric simulation model.The mechanical properties prediction model of propellants is established based on the elastic VCFEM.The elastic VCFEM and homogenization method are combined to estimate the effective modulus and effective Poisson's ratio of propellants.The common finite element methods and classical analytical model are used to verify the correctness of this prediction model.In order to eliminate the disturbance caused by model uncertainty,the Monte-Carlo theory is introduced to calculate the mechanical properties of RVE models generated randomly.The effect law of microscopic parameters,i.e.the mass fraction and grading of inclusions on effective mechanical properties of propellants is analyzed.The VCFEM with transition phase is developed to analyze the influence of thickness and transition functions of transition phase on effective modulus and effective Poisson's ratio of propellants.Based on the simplified viscoelastic VCFEM,the prediction model of mechanical properties of propellant is established.A RVE model construction method for simplified viscoelstic VCFEM is developed by using centroid Voronoi mesh method.The variable step size time domain adaptive algorithm is improved to establish a prediction model for predicting the mechanical properties of propellants based on simplified viscoelastic VCFEM.The prediction model is used to analyze the influence of microscopic parameters such as inclusion phase content,component material properties and structural morphology on the effective creep compliance of propellant.A prediction model for the mechanical properties of propellants based on viscoelastic VCFEM with inclusion phase is established.The discrete form of Prony series viscoelastic constitutive model in time domain is derived.A prediction method based on viscoelastic VCFEM is proposed to estimate effective relaxation modulus.The stress concentration factor is calculated by using the stress field of the RVE model.The influence of matrix's initial modulus,the mass fraction and the inclusion's size and mass distribution on the mechanical properties of the propellant is explored with this model.An optimization method based on the 3D matching prediction model of propellant is reconstructed to design mechanical properties of propellants.To meet the need of design of propellant's mechanical properties,a RVE model constrcuion method based on the matching transformation between 3D and 2D.The relaxation experiements and constant speed tenslile tests are carried out to bulid a 2D to 3D correction model.A design-oriednted prediction model is established finally.The neural network and genetic algorithm are employed to develope an optimization algorithm.It contains three stages of parameterd seltection,initial design determination and local optimization.An application example is used to detail its procedures and to verify its feasibility.The research results here can provide an important reference for the prediction and design of mechanical properties of solid propellants.The prediction and design methods have a good engineering applications prospect and can be adapted to other similar particle reinforcement materials.