| The electrical explosion of metals is attractive due to the unique state of metals under rapid heating with high inner energy offers the opportunity to investigate physical phenomena undiscovered other-where and its wide applications in fields such as pulse technique, exploding dynamics, new material preparation and others.In the present work, theory of electrical explosion of metals, related numerical simulations and experiments have been implemented and the following conclusions can be done:1. Recapitulative descriptions of the electrical explosion process of metals have been done and the disappearance of metal’s conductivity is discussed. This is helpful to give a clear physical impression of the metallic foil exploding process in electrical gun experiments.2. Based on the one dimensional reaction hydrodynamics program SSS, a magnetohydrodynamics code has been developed incorporating with tabular EOS and Burgess resistivity model considering multi-phases using a unified set of modified resistivity coefficients for aluminum (or cooper) foils to calculate the metallic foils exploding process in EGs and the launching process of two-stage metallic flyers in TSEGs. Calculated results are widely compared with experimental data of ours and those reported in literatures in past decades, good agreements indicate that this model is applicative universally in calculations of EGs with aluminum or copper bridge foils in size ranging0.76×0.76mm2～30×30mm2, burst current7.8kA～1MA and EGs’ flyer velocity2km/s～18km/s. Utilizing the MHD code, effects of metallic foils’ materials on plastic flyers’ final velocities and contributions of Lorentz force to the flyers’ acceleration are analyzed. Calculated results indicate that the acceleration ability difference of foil materials may be attributed to the adiabatic indexes of expanding foil plasmas, and if the linear density of burst current is much smaller than that of maximum current and its absolute value is large enough (for example,>50kA/mm), the Lorentz force may cause a second acceleration of plastic flyers.3. The process of metallic foil exploding driven planar plasma jet is calculated by the MHD code mentioned above and the parameters in the process, such as particle velocity, plasma density and the momentum of the plasma are computed. Calculated results show that a thin layer with high density following by high temperature and high pressure plasma is projected to a speed up to60km/s. The course of plasma jet impacting an aluminum foil target is calculated also and the computed results coincide with the experimental results.4. The two staged electrical gun(TSEG) technique has been developed to launch thicker metallic flyers. The key factors in the TSEG launch process, such as the separation of metallic flyer and attenuator and the adjustment of metallic flyer to insure its integrity and stable speed, are explored in detail by simulations and experiments. Composite attenuators are proposed to solve these problems and good results are obtained.5. Impact dynamic behaviors of the Zr51Ti5Ni10Cu25Al9bulk metallic glass have been studied under different impacting velocities using0.5mm thick polymers flyer accelerated by the14.4kJ EG. Disparate elastic-plastic behaviors are observed and the Hugoniot curve in8GPa-17GPa stress range has been measured. Compared to the Hugoniot curve reported in literature in stress range18GPa to110GPa, it is found that the Hugoniot curve slopes in different stress range are different. Meanwhile, experimental results show that the unloading wave speed increases with impact stresses. Utilizing the TSEG, dynamic behaviors of Zr51Ti5Ni10Cu25Al9and Zr41.2Ti13.8Cu10Ni12.5Be22bulk metallic glasses are studied by stainless steel flyers planar impacts in velocity range100m/s-300m/s. Macroscopic observation and the SEM image of the fracture surfaces indicate that dynamic behaviors of the two Zr based bulk metallic glasses act as brittle, which means that they are not suitable in impacting situations.6. Systematic experimental study were performed using Gleeble3500thermal-mechanical testing system to study the effects of heating rates on mechanical behaviors of Zr51Ti5Ni10Cu25Al9bulk metallic glass under pre-load. Experimental results show that the failure models of this material change from heating soften to catastrophic rupture with increasing pre-load and heating rate. Under the pre-stress which is much lower than the material strength at room temperature and rapid heating, it is found that the sample cracks dramatically at the temperature close to or above the material’s glass transition temperature. The relations of yield temperature and heating rate as well as pre-stress are deduced based on amorphous alloys structure relaxation theory under changing temperatures. Metallographic observation of recovery samples show that the catastrophic rupture is caused by the overlap of heat dis-match stress and concentration stress caused by pre-load in defects concentrating regions, a critical failure model is given out also. |
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