The Micro-Meso Multiscale Simulation Of Mechanical Properties For Polymer Matrix Particle Composites

Polymer matrix particle composites consist of polymer matrix and particulate reinforcements such as inorganic,organic materials or metal materials.Polymer composites have both excellent wear-resisting and heat-resisting properties of the polymer and high stiffness of the particle due to the addition of ceramic or metal particles into polymer matrix,which can strengthen the creep resistance and fracture toughness of composites.Particle reinforced polymer composites are expected to be applied to biomedicine,aerospace,battery energy fields and design for high performance explosive.Therefore,it is significant to study the mechanical and thermodynamic properties of particle reinforced polymer composites.The thesis proposes a micro-meso sequence multiscale simulation method to study the mechanical properties of polymer bonded explosive(PBX)and hydroxyapatite/polyetheretherketone(HA/PEEK)biocomposite material.In this multiscale model,molecular dynamics is used for calculating various properties of particulate materials and polymeric materials in microscale.The accuracy of molecular dynamic simulation results at microscale are verified by comparing with experimental results.Key model parameters are then obtained for mesoscale simulation from microscale calculation.Material point method is applied to study the mechanical properties of composites with mesoscale representative volume element models and further quantative study the microstructure influencing on the constitutive relations,equation of states and fracture mechanisms of composites.Using the micro-meso multiscale method,simulations of PBX and HA/PEEK biocomposite are performed,the main results are as follows:1.The compression moulding simulation of PBX shows that the change rates of average temperature and stress have positive relations with initial packing rates.The moulding process consists of two stages,namely the densification process and the deformation process.The stress between particles is transmitted downward through the force chain networks,which leads to the heterogeneous distribution of temperature and stress fields.Simulation results predict evolutions of stress and temperature fields of PBX with high packing density,especially near the theoretical density,which provide reference data for experimental researches.2.The uniaxial compression simulations of TATB/F2314 PBX show that the calculated elastic modulus and compressive strength of PBX at different temperatures and different porosities are in consistent with experimental data and other numerical simulation results.With the increasing of porosity and temperature,the elastic modulus and compressive strength of PBX decrease significantly.Variations of compressive strength with temperature are applied to develop the elastoplastic constitutive equation of PBX with temperature effect factors.Based on the Hashin-Shtrikman equation,the elastic modulus with different porosities can be used to predict shear and bulk moduli of PBX with different densities.The establishment of the constitutive equation and prediction results provide reliable parameters for the macroscale simulations.3.The isothermal and high-pressure compression simulations of HMX/Estane PBX show that isotherms and shock Hugoniot data of pure HMX material and PBX are both coincide with experimental and numerical simulation results,which verify the correctness of multiscale method proposed in this thesis.With the increasing of porosity and binder volume fraction,the compressive pressure decreases,and the decreasing effect is highly dependent of porosity.Isotherms with different porosities and binder volume fractions are used for effective parameters fitting of Birch-Murnaghan equation of state of PBX.The bulk sound velocity and dimensionless parameter of Mie-Grüneisen equation of state with microscopic effect factors is fitted according to the shock Hugoniot data.4.The shock loading simulation of HMX/Estane PBX show that with the increasing of impact velocity and decreasing of porosity,the stress peak value gradually increases,which resulting in a severer damage of PBX and higher local temperatures during material fractures.When shock loading is stopped,a strong tensile zone is generated under the propagation and interaction of unloading stress wave and reflection wave,which can cause the initiation of material fracture once the dynamic strength of PBX is satisfied.The damage degree of PBX is mainly dependent porosity and impact velocity,while the binder volume fraction generally affects the fracture patterns.Different mechanism of hotspots can be analyzed from evolution of temperature fields at different impact velocities,porosities and binder volume fractions.5.Simulation results of mechanical properties of HA/PEEK biocomposite show that with the increasing the volume content and diameter of HA particles,the tensile strength and toughness of HA/PEEK composites decrease significantly and the ductile-to-brittle transition is then observed.The stress-strain response of HA/PEEK composites has an obvious tension/compression asymmetry.HA particles can provide the strengthening effect on mechanical properties of HA/PEEK composites with the costs of tensile strength reduction.The simulation results are basically consistent with experimental results,which validates the applicability of the multiscale simulation method for particle reinforced polymer composites proposed in this thesis.This thesis establishes a micro-meso sequence multiscale simulation method to study the mechanical properties of particle reinforced polymer composites.The influencing of microscopic effect factors on equation of state,constitutive relations are fitted and predicted by multiscale simulations.Furthermore,responses of temperature and stress fields of polymer composites under compression loading and shock loading are analyzed at mesoscale.Compared with previous experimental results,the accuracy and practicability of multiscale simulation method can be verified.This thesis provides support and guidance to mechanical properties of the experimental research and macroscale simulations in advanced particle reinforced polymer composites.