Study On The Jet Mechanisms Of Shaped Charge With Porous Liner And Its Applications

Shaped charge effect is broadly used in military arena and civil construction, because the focusing of the detonation products creates an intense localized force and decays slowly. As a critical part of the warhead, property of the shaped charge liner has great effect on the application of the shaped charge effect. The jet property and penetration mechanism of shaped charge with porous liner were studied systematically with experimental, analytical and numerical methods.Equation of state (EOS) of the porous material is key to the shock temperature rising calculation. All of the EOS of porous materials in the open literatures were analyzed and compared, the merits of which and application conditions were discussed. Because of the few parameters and accuracy, the EOS of Griineisen revised by Herrmann was selected.Porous material property shocked was studied and analyzed. Approximated jet speed calculation method was presented and compared with the measurement results. It is shown that the lower speed with porosity increase may be caused by the energy dissipation and degradation of the shocked pressure.Porous nature considered, the criteria for the jet coherence were presented, that is, the collapse flow speed must be less than the sound speed, which is after the shock wave compressed and released. The condition for the jet coherence produced by the shaped charge liner made up of low melting point was put forward, that is, sound speed satisfied, and the shock temperature rising after collapse must be less than the material evaporating point to avoid the phase transformation from liquid to vapor, which is helpful for the shaped charge design.The jet stability produced from shaped charge with porous liner was studied theoretically, compared with X-Ray measurement and penetration test, it is shown that proper porosity can decrease the jet dynamic strength and enhance the breakup time. Penetration Compared with the homogeneous liners, the deeper penetration mechanism at low standoff distance was presented ,that is, the shock temperature rising can decrease the viscosity of the high-speed part.Concept of shaped charge granular jet was presented. Based on the assumption of density locking model, the penetration model of granular jet was put forward, which covers shortage of the classical theory, and can become any of all the forms under certain condition.The slug microstructures was examined by optical microscopy and electronic scanning microscopy and compared with the spanned homogeneous one, it reveals that the dynamic recrystallization is the main plastic deformation mechanism at great high-strain-rate, and initial temperature rise is helpful for the dynamic recrystallization. The great shear deformation at the separated location of jet and slug was also observed.A nonlinear finite element software LS-DYNA was used to simulate the initiation of confined explosive penetrated vertically by shaped charge jet, the physical property is analyzed systematically. Calculations show that, jet head shape effect on the initiation depends on the covered plate thickness and it has no effect on the initiation when the plate thickness is ascertained and jet diameter is less than some value. For the jet initiation with different density, the less the density and the thicker plate, the higher is the speed. The plate density becomes less important with the higher jet speed.Based on the analysis of the interaction between jet and flying plate, a physical model for calculating the intermittent disturbance frequency was presented. The parameters such as NATO-angle, plate velocity and hardness were analyzed; the transition condition from intermittent to continuous disturbance was put forward.This work is of significance and guidance for the design and application of shaped charge with porous liner in the future.