Numerical Simulation Of PBXs’ Macro-meso Mechanical Behaviors

In this paper,ANSYS/LS-DYNA software was used to simulate the mechanical behaviors,deformation and failure of polymer-bonded explosives(PBX)under quasi-static and dynamic loading conditions at macro and micro-scale level.The real microstructural model based on the digitized micrographs of PBX was set up by digital image processing technology.In the region of PBX that tend to damage and crack formation,the real microstructural was used,and the macro model was used in the area far away from damage.A macro-micro that not only can describe the mechanics behavior of PBX explosives accurately,but also save computational resources and time was established by coupling the boundaries of the real microstructural and macro model with CONTACT＿TIED＿NODE＿TO＿SURFACE command in LS-DYNA.Constitutive theory of particles,binder and the macro portion of PBX explosive were studied.The plastic kinematic constitutive formulation was used for particles,the viscoelastic constitutive formation was used for binder and macro portion.The viscoelastic model parameters of the binder and macro portion were obtained respectively by fitting the experimental results obtained in the literature.Three macro-micro model of semi-circular bending,three-point bending and uniaxial tensile test were established to simulate the deformation,fracture and mechanical properties of PBX under quasi-static and dynamic loading conditions with the process of element delete.Based on macro displacement and strain fields,micro strain fields,loading forceloading time curve and stress-strain curve obtained in the simulations,the deformation and fracture behaviors of PBX were studied.The microsopic fracture behaviors of PBX were studied.The fracture toughness of PBX was calculated using semi-circular bending and three-point bending.The results show that semicircular bending was more suitable to measure the fracture toughness of PBX explosives than three-point bending.The differences of PBX explosives’ mechanical properties and failure mechanism between dynamic and quasi-static conditions were analyzed.We found that in the condition of quasi-static degree of particle damage,proportion of cracks that undergo transgranular fracture,fracture toughness,fracture stress and the effective modulus of elasticity were significantly reduced.The numerical simulation of the semi-circular bending test under different prestressed crack lengths,pre-crack tip shapes and different strain rates and uniaxial tensile test under different strain rates were conducted.The influence of different conditions on the mechanical behavior and fracture toughness of PBX explosive was analyzed.It is found that the tensile failure strength,elastic modulus and fracture toughness show strong strain-rate dependence.The numerical simulation results were compared with the experimental results,which was in good agreement.