| Condensed matter usually behaves like a fluid under extreme conditions,and its internal dynamic characteristics are usually described by the conservation equations of momentum,mass and energy.When a system of fluid dynamics equations is solved,it is necessary to know the state equation and transport properties of the material in advance,such as viscosity coefficient,thermal conductivity,and electrical conductivity.Therefore,the main purpose of this paper is to use flyer impact perturbation experiment which is relatively mature and easy-to-operate to measure the shear viscosity coefficient of materials under shock high pressure.Usually,the equivalent viscosity of a continuous medium is closely related to its momentum transfer and energy dissipation,and these physical quantities depend on the structure of the material,so variation of the viscosity of the material with the shock pressure is inextricably linked to its structure.Therefore,the metal tin of lower melting point is selected in this paper.In the process of summarizing the variation of its equivalent shear viscosity coefficient with the shock pressure,the possible relationship between the equivalent shear viscosity of metal tin and its structure is analyzed.A brief summary of the work done in this paper and its corresponding results is as follows:1.The evolution process of the perturbed shock wave front in Miller flow field,Sakharov and flyer-impact is numerically simulated by solving two-dimensional hydrodynamic equations.The results show that: 1)In the flyer-impact and Sakharov initial flow field,the spatial distribution of the relevant physical quantities is extremely complex,and it is impossible to analyze the evolution law of the disturbance amplitude of the shock wave front in the above experiments with Miller’s analytical solution.2)The shock wave disturbance attenuation curve is affected by many factors such as shock pressure,initial flow field and material/viscosity/wavelength of the sample.Under certain other conditions,the zero-amplitude point of the shock wave disturbance attenuation curve is very sensitive to the viscosity of the sample in the flyer-impact and Sakharov experimental flow field.2.The key in the discrete electrical probe measurement device is the circuit.the Simulink simulation module of MATLAB is used in this work.It is found that among the four factors affecting the voltage drop relaxation time,high connection line inductance and low resistance value of the resistor array is the key to prolonging the relaxation time of the voltage falling edge,and this result provides a reliable theoretical support for the experimental improvement of this work.In order to further improve the interpretation accuracy of the voltage signal transition point,a parallel circuit is designed.3.Based on the two-stage light gas gun experimental platform,the flyer-impact disturbance experiment design is adopted,and the discrete electric probe device is used to measure the amplitude of the disturbance shock wave front evolutionary laws in the metal tin sample under the condition of the shock pressure of 25～65 GPa with the propagation distance.The quantitative relationship between the shear viscosity coefficient of metallic tin and the relative position of the zero-amplitude point of the shock wave front,which was obtained under the same experimental conditions.The equivalent shear viscosity coefficient values are determined to be 119.63±79.97 Pa·s(25 GPa),1228.06±85.42 Pa·s(36 GPa),922.66±88.68 Pa·s(43 GPa),1055.65±94.11 Pa·s(54 GPa),and 1805.19±99.52 Pa·s(65GPa).4.Under the condition of shock pressure of 25～65 GPa,the equivalent shear viscosity coefficient value of metallic tin increases with the increase of shock pressure in the single phase region.And there is a sharp change in the viscosity coefficient near the phase boundary.It is basically consistent with the experimental results of sound velocity.Based on the sensitivity of the shear viscosity coefficient of metal tin to its structure,by extension,the variation law of the viscosity of the material with the impact pressure can be the basis for judging the phase transition of the material. |
