| The loading of magnetically driven can be used to realize the launchment of hypervelocity flyer plates,quasi-isentropic compression and cylindrical liner implosion by different loading configurations.Correspondingly,it can realize different thermodynamic loading paths such as shock compression,quasi-isentropic compression and shock-quasi-isentropic compression,which can be used in many research fields of material dynamics at extreme conditions,laboratory simulation of space shielding on hypervelocity impact and high energy density physics.The experimental techniques of magnetically driven and dynamic behaviors of polystyrene were researched in deep in this dissertation.Firstly,the precise experimental techniques of one-dimensional strain shock loading and small size liner implosion driven by magnetic force were further researched and established based on the stress wave theory,magnetohydrodynamics simulation and experiments.Then,the physical and mechanical properties of polystyrene at high pressure and high loading strain rates were studies by mean of the magnetically driven shock loading method developed in this dissertation.The important progresses and innovative results are shown in following:1)The precise experimental techniques of one-dimensional strain shock loading driven by magnetic force were further developed and established based on the compact pulsed power generator CQ4,which provided a technical approach for studying experimentally on the dynamic properties of materials and hypervelocity impact phenomena.Based on the electrical parameter characteristics of the self-developed compact pulsed power generator CQ4,the electromagnetic,mechanical and thermal distribution characteristics of the magnetically driven planar load structure were analyzed in depth using 3D Ansoft Maxwell electromagnetic field analysis software and LS-DYNA 980 magnetohydrodynamics simulation program.An optimized electrode structure for one-dimensional planar shock loading was proposed.The characteristics of flyer velocity,planarity and effective thickness were researched in experiments.The flyer with 10 mm wide×0.7 mm thickness was accelerated to 7km/s with good planarity in center diameter of 6mm and effective thickness of 0.44mm.The uncertainty of shock Hugoniot was analyzed.In typically experimental results,the uncertainty of particle velocity is less than 2%?k=2?,and the uncertainty of shock wave velocity is less than 4%?k=2?,which meet the requirements of precise shock physical experiments.Based on this,more work was done to launch an aluminum flyer plate with initial size of l0×6×0.33mm to hypervelocity of 18km/s on CQ4.2)The experimental technique of magnetically driven small-size liner implosion was developed and established on CQ7.Hundreds of Tesla ultra-high strong magnetic field technology was realized by compressing quasi-static magnetic field.An experimental technique is provided for the study of ultra-high pressure equation of state and new magnetically driven fusion concept.The cylindrical liner load with low inductance and uniform magnetic field was designed and developed for liner implosion experiments.An optical fiber pin with diameter of 1.5mm was developed for measuring liner implosion velocity.The liner with inner diameter of 6.2 mm and thickness of 0.4 mm was accelerated to 10.02km/s at charging voltage of 75kV on CQ7 before loss of the reflected beam.The azimuthal symmetry was characterized by means of laser high speed photography system and velocimetry.The experimental results showed that the measurement points deviated about 0.030mm from azimuthal symmetry of liner.And the azimuthal symmetry of liner kept well.Based on the technique of magnetically driven liner implosion,high pulsed magnetic field of hundreds of Tesla was realized through magnetic flux compression.And a high pulsed magnetic field up to 357T was obtained by compressing a 8.84T magnetic field with rising time of lms in experiments.3)Using the developed and established magnetically driven one-dimensional precision physics experiment technology,the complete equation of state,dynamic yield behavior,refractive index and effective polarizability of polystyrene under high pressure and high strain rate conditions were studied in experiments and theories.Some new scientific understanding of polystyrene was obtained,which laid the foundation for its better engineering applications.a)The complete equation of state of polystyrene was established based on the Helmholtz free energy model.The complete equation of state of polystyrene was established based on the Helmholtz free energy model with describing the state before and after the dissociation of polystyrene respectively.The equation of state was validated by the physical quantities of Hugoniot and Lagrangian sound speed which obtained from the magnetically driven shock and re-shock experiments.The obtained complete equation of state can describe well the high pressure response of polystyrene in pressure range of 500GPa.The shock temperature was calculated respectively from the free energy model,the mixture method and thermo-dynamical approximately calculation.The comparison of shock temperature shows that the thermodynamic behaviors of polystyrene are described well by the free energy model.b)The yield behavior of polystyrene at strain rate of 106/s was obtained by means of the technique of magnetically driven quasi-isentropic compression.The Lagrangian sound speed and quasi-isentrope of polystyrene were obtained by means of the technique of magnetically driven quasi-isentropic compression on compact pulsed power generator CQ-4.The relationship between Lagrangian sound speed and particle velocity is linear above velocity of 200m/s and is non-linear below 200m/s.By analoging with uniaxial stress experiments,the strength?flow stress?for uniaxial strain loading can be defined in terms of the difference between the longitudinal stress and pressure.The initial yield strength of PS is derived to be 0.16GPa at strain rate of 0.7×106/s.The hydrodynamic simulations were conducted to describe the dynamic response of PS including the Mie-Gruneisen equation of state and Steinberg-Guinan strength model.The yield response of PS under quasi-isentropic compression can be described well in our simulations,which shows excellent agreement with the experimental data.The yield stress under quasi-static compression and Hopkinson bar were obtained.The strain rate effect of polystyrene was discussed.The yield stress of polystyrene is weakly dependent on strain rate.This observation implies that the transion of PS occurs at a very low temperature.c)The refractive index of polystyrene under shock compression was obtained in experiments.The polarizability,lowest direct band gap and the main reason of dissociation were analyzed by the equation of state,Lorentz-Lorenz equation and a single effective oscillator model.The refractive index,molecular polarizability and thermodynamic response of polystyrene under shock compression were investigated through experiments and theoretical analysis,and a relationship between the refractive index and the density,pressure and temperature of the polystyrene was obtained.At pressure above 20GPa,an obvious inflexion was observed that the refractive index of the polystyrene varied with the thermodynamic variables;in particular it was found to depend strongly on the temperature?as derived from a semi-empirical complete EOS?.Relating the measured refractive index to the polarizability indicates that the polarizability decreases from 1.28×10-23cm3 at ambient conditions,to 0.98×10-23cm3 at pressure of 33GPa,indicating the lowest direct band gap E1 of polystyrene becomes<2eV,similar to that of many semiconductor materials. |
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