Meso-mechanical Behavior Simulation Study Of Polymer Bonded Explosive(PBX)

Polymer bonded explosive(PBX)is a mixture explosive consisting of single crystal explosive particles and polymer binder.The mechanical properties have an important influence on the reliability and safety of PBX.Numerical simulation is an important method to study the meso-mechanical behaviors of PBX.The numerical manifold method(NMM)can be used to simulate the discontinuous mechanical behaviors of materials by two sets of independent cover systems and truncated discontinuous cover functions.In this thesis,the establishment of PBX meso-structure models,and realization of the constitutive models of the polymer binder and the particle/binder interface in the NMM are studied.Then the characteristics and rules of the meso-mechanical behaviors of PBX are simulated and analyzed.Firstly,the finite element mesh is adopted to generate NMM mathematical covers so as to avoid the appearance of too-small manifold elements,and an independent cover method is also put forward,in which a single material domain is described as one manifold element.The coupling use of different cover types ensures the NMM simulation models to be generated more reasonably,and reduces the number of manifold elements and contact numbers along discontinuity surfaces,thus helps to improve the NMM computational efficiency.Secondly,the ZWT visco-elastic constitutive model,the Prony series visco-elastic constitutive model for the PBX binder and the bilinear contact relationship model for the particle-binder interface are realized in NMM.The correctness of the visco-elastic constitutive models under different loading rates is verified.The accuracy of the bilinear contact relationship model is verified by the normal/tangential contact force–displacement curves obtained.Finally,the meso-structure model of PBX is established by two ways,and PBX meso-structure models of different particle size distributions,particle volume fractions and particle distributions are simulated under uniaxial tension and compression conditions.The results show that the growth rate of macro-equivalent stress increases with the increase of the particle volume fraction,that is,the equivalent elastic modulus of PBX increases as the particle volume fraction increases.Interfacial debonding and binder fracturing are the main failure modes,and small explosive particle breakage can be considered as one major failure mode during the initial stage under uniaxial compression as well.For models with similar particle volume fraction but different meso-structures,different macro-equivalent tensile/compressive strength will be obtained.Because the different dominating degree of binder and explosive particles in the process of PBX deformation,the variation of PBX macro equivalent modulus in different volume fraction segments is caused.