Study On The Micromechanical Methods To Predict The Mechanical Propert)y Of Polymer Bonded Explosives

Benefiting from its excellent comprehensive performance,polymer bonded explosive(PBX)is widely used in rocket propellants and warheads of weapon system,and its mechanical property is of great concern.Although microscopic experimental and numerical studies are common,theoretic studies mainly remain on macroscale.The macro phenomenological constitutive relations based on continuum mechanics cannot uncover the inherent relation between micro-structures and macro responses.Therefore,it is of great significance to develop micromechanical methods for predicting the mechanical behavior of PBX.Macro behavior will be better understood by carrying forward the theoretical study into microscale,and this is an inevitable trend in future research.In order to find out whether the existing micromechanical methods are suitable for predicting the effective elastic property of PBX,bound methods and analytic methods are adopted first.For PBX,the particle volume fraction is generally higher than 80%,the Young's modulus of particle is 3?4 orders of magnitude higher than that of the binder,and the particle sizes are ranging from 1 ?m?1000?m.When classical methods are employed,all these factors lead to inaccurate estimations.Parametric analyses of ingredients' elastic constants show that the property of explosive particle has little impact on the overall effective moduli,but the property of binder is of great influence.On the basis of classical micromechanics,strain concentration tensor and Eshelby tensor are modified to consider the influences of particle interactions and particle shape,respectively.After the spring interface model is introduced into the framework of micromechanics,elastic moduli of PBX with imperfect interfaces are weakened in the form of degradation factor.The shear moduli are independent of the interfacial normal compliance just as the bulk moduli independent of the tangential compliance.With bigger compliance,larger decrease in the modulus can be seen;and the influence of weak interface increases as particle fraction goes high.In the calculation,the degradation in effective property is caused by the additional strain and modified Eshelby tensor under imperfect interfacial condition.However,for PBX,modification of the Eshelby tensor can be ignored,the additional strain is the only key factor that leads to the degradation.Thus a simplified method can be derived,which brings out almost identical results as the original method.According to the micro structure of PBX,explosive crystals coated by binder layer are viewed as equivalent particles,and PBX is a kind of "pseudo polycrystal”consisting of equivalent particles without matrix.A pseudo polycrystal method is proposed to predict the effective elastic moduli of PBX,which has introduced the defects and particle size character.When it is applied to PBX9501 and X0242,better estimations are attained.Moreover,this method is suitable for PBXs with different particle size distributions.Impacts of particle spatial distribution and particle shape are investigated by representative volume element.Their influences are strengthening as particle content rises,so the microstructure of PBX should be modeled adequately.Voronoi model consisting of irregular polygonal particles is established.With similar microstructure and adjustable particle fraction,Voronoi model gives out favorable estimations for effective elastic moduli.Binder hybridizing method,which establishes a particle dual-disperse model preliminarily,is proposed to investigate the effect of fine particles on the effective property.The structure of fine particles is prone to form stress-bridges inside the RVE,which restrain the local deformation and lead to enhancement in macro stiffness.