| There are fluids at different depths of the earth’s crust.The existence of these fluids is believed to control the earth’s magmatism,seismic wave propagation,ore evolution and even plate drift to a large extent.As a metal element in the earth’s crust that is second only to oxygen and silicon,the study of its viscosity coefficient is of great significance for exploring the propagation process of seismic waves in the earth’s interior and the rheological properties of the earth’s interior.So far,people have conducted some studies on the viscosity of substances under extreme conditions.Among them,the viscosity coefficients of various metals and their compounds calculated by molecular dynamics are usually in the order of 10-3～10-2Pa·s;The magnitude of the viscosity coefficient of the material measured by the static high pressure experiment represented by the falling ball method is also 10-3～10-2Pa·s;In geosciences,geoid and other methods are used to calculate the order of magnitude of the viscosity coefficient of geological materials to be about 10-22Pa·s.Due to the huge differences in the viscosity coefficients obtained by different methods and the lack of regular knowledge,it is necessary to further explore the law of viscosity changes of substances under high temperature and high pressure conditions.In this paper,based on the flyer-impact perturbation experiment,the geometric similarity method is used to study the shear viscosity of metal aluminum under high temperature and high pressure conditions.In the experiment,improve the electric probe measurement technology to improve the accuracy of voltage signal interpretation;improve the insulation method between the sample and the probe to minimize the gap between the two;replace the resistors,capacitors and other components to reduce the circuit inductance to the signal Impact.In theory,the attenuation process of the sinusoidal disturbance shock wave in the sample under different experimental conditions is analyzed by the numerical solution of the two-dimensional flow field,and the influence of the initial flow field,shear viscosity,intensity effect,disturbance wavelength and geometric similarity ratio on the disturbance amplitude is analyzed.The influence of evolution,and then scientifically and rationally design the geometric size of the experimental sample and analyze the shear viscosity of the sample under impact and high pressure.The improved experimental device was used to successfully obtain the evolution of the shock wave front in the sample aluminum under the pressure of 61-88 GPa,and the zero amplitude value of the disturbance attenuation curve was measured.Combined with the quantitative relationship between the zero amplitude value obtained by numerical analysis and the shear viscosity of metallic aluminum,the equivalent shear viscosity coefficient of aluminum under 61 GPa,64 GPa,75 GPa,83GPa and 88 GPa impact pressures is determined to be 3500±50 Pa·s,3080±50 Pa·s,4200±60 Pa·s,5520±60 Pa·s,6750±70 Pa·s,obviously,the equivalent shear viscosity coefficient of metal aluminum increases with the impact pressure and increase.Compare the attenuation of shock wave disturbance in samples with geometric similarity.When the shock pressure is 61 GPa and 76 GPa,the phase shift value of the zero amplitude point of the disturbance attenuation curve is 0.1082 and 0.0679,respectively.The phase shift value and material shear under certain pressure are used.The quantitative relationship between the viscosity coefficients can be analyzed and the shear viscosity coefficients of metallic aluminum are 1850±300 Pa·s and 2000±300Pa·s,respectively.The shear viscosity coefficient of aluminum obtained by the geometrical similarity method is significantly lower than that of the conventional flyer-impact perturbation method.Therefore,the influence of the strength effect on the shock wave perturbation amplitude cannot be ignored before the material is melted. |
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