Investigations On Damage And Initiation Mechanism Of PBX Charge During Penetration

Earth penetrating missile(EPM)is a kind of weapon that strike underground targets.It penetrates high-strength bunkers and detonates its explosive charge once it reaches a predetermined depth.Polymer bonded explosive(PBX)is commonly used as the charge of the EPM.It consists of energetic particles,polymer binders and desensitizing agent.Mass density discontinuity surfaces and meso-scale defects form during preparation and manufacturing of the PBX.The PBX charge would undergo overloads during penetration.Material damage would initiate and evolve due to the existence of the mass density discontinuity surfaces and meso-scale defects.Coupling of mechanical,thermal and chemical effects results in high temperature in the damaged regions in PBX.Initiation or even detonation might occur in PBX.It leads to early explosion of the EPM and failure of strike missions.Penetration stability of the EPM charge is closely related to the mechanical,thermal and chemical properties of the PBX material.In this paper,the characteristics of dynamic damage,initiation,reaction dynamics of a new energetic material PBX1314 and the penetration stability of PBX1314 is investigated.The research in this paper mainly include the following:(1)On the basis of marco-scale dynamic responses and meso-scale damage morphology of PBX1314 in dynamic mechanical property experiments,the relation between evolution of microcracks and the marco-scale dynamic responses is studied and a dynamic damage and initiation model of PBX1314 is constructed.Dynamic responses of PBX1314 in several stress states are predicted.Investigation on bulk temperature increase and localized temperature increase are carried out.Distribution and evolution of temperature near a microcrack due to energy localization are analyzed.The results indicate that deformation and growth of microcracks in meso-scale lead to the differences of the dynamic tensile and compressive mechanical behavior and damage accumulation of PBX1314 in marco-scale.Microcrack interfacial friction play significant roles in heterogeneous heating property of PBX1314.A heterogeneous heating initiation criterion of PBX1314 is presented based on microcrack friction mechanism.(2)Cylinder tests of PBX1314 are performed.Radial displacements of the copper cylinders are recorded.Isentropic expansion behaviors of PBX1314 detonation products are studied.Equation of state of PBX1314 detonation products is constructed and the corresponding parameters are obtained.Steady propagation of detonation wave in PBX1314 and deformation of the copper tube is numerically simulated.The constructed equation of state of PBX1314 is examined.The results show that the Chapman-Jouguet pressure of PBX1314 detonation products is lower when compared with other energetic materials with RDX.It suggests that the lower pressure is due to the low percentage of RDX particles in PBX1314.(3)Lagrange experiments are performed to obtain pressure histories in the path of shock detonation transition in PBX1314.The experimental data are transformed to be reaction fraction information based on equation of state of reactants,equation of state of reaction products and a mixture rule.A reactive flow dynamics model of PBX1314 is presented and parameters are obtained.The reactive flow dynamics model of PBX1314 is verified by the expanded application of the designed initiation and energy release property experiments.The results indicate that the reactive dynamics model of PBX1314 could be constructed by using flying plate experiments,cylinder tests,Lagrange experiments and initiation and energy release property experiments.A systematic method to determine the reactive dynamics properties of a newly-designed PBX is presented.(4)The HJC(Holmquist-Johnson-Cook)concrete constitutive model is implemented into ABAQUS.In combination with the dynamic damage and initiation model and the reactive flow dynamics model,a finite element model of an EPM filled with PBX1314 penetrating a concrete targets is constructed.Penetration of the EPM into the target is numerically simulated.Bulk deformation of the PBX1314 charge,dynamic responses of microcracks in the charge,and the correlated damage and initiation during penetration are researched.Reaction process in the initiated regions in the charge is studied.The numerical simulation results of the model are examined by penetration experiments.In the results,the PBX1314 charge undergoes multiple compression-rebound deformation cycles.Multiple impacts with the shell make the tail of PBX1314 charge be the weakest region that threatened by structural damage and ignition.