Study On Micro-mechanism Of Characteristics Of Metallic Tin Micro-jet

The problem of microjetting generated at the defect under dynamic loading is closely related to the weapon manufacturing process,which is an important subject in the current engineering application research,and has important practical significance for the research of microjetting.In this paper,the jetting processes of single-crystal tin and polycrystalline tin are studied by molecular dynamics simulations.Firstly,the jetting processes of single-crystal tin with sinusoidal surface defects was studied under laser and plane impact loading.By analyzing the physical information such as jetting factors,spike velocities,bubble velocities,and sample microstructure characteristics,the similarities and differences of metal tin jet characteristics under two loading conditions were systematically studied,and the internal reasons and physical mechanism of the differences were revealed through in-depth analysis of numerical simulation results.Secondly,the jetting process of polycrystalline tin was numerically simulated,mainly to investigate the difference between the jetting process of polycrystalline and single-crystal tin under different impact velocities,it is beneficial to the further analysis of the experimental results.In the aspect of single-crystal tin numerical simulation,the hugoniot curves of 2NN MEAM potential is firstly calculated.Then,based on the piston and energy layered deposition methods,the computing models of tin microjet under plane impact and laser loading were established respectively,and the similarities and differences of jetting results under plane loading and laser loading were compared.The simulation results are compared with the experimental and theoretical results.The simulation results show that the jetting factors of both loading modes increases first and then reaches saturation with the increase of impact pressure.However,the jetting factor under laser loading reached saturation value at relatively low impact pressure compared with that under plane loading,which was consistent with the experimental results.Structure analysis via x-ray diffraction and radial distribution function techniques indicates that the laser loading leads to higher melting degree,which further facilitates the jetting process.Under the two loading modes,the spike velocity has a linear relationship with the impact pressure.In contrast,bubble velocity varies with different loading modes.The simulation results reveal the basic mechanism of the jetting process of the two loading modes,which is helpful to deepen the understanding of the microjetting phenomenon.The numerical simulation results of polycrystalline tin are compared between single crystal and polycrystal tin under plane impact loading.The results show that when the impact pressure is low,the non-uniform melting and attenuation of the front edge of the shock wave will occur due to the defects of different grain orientation and grain boundary,and the non-uniform melting will lead to the deviation of the jet.The spike velocity,spike velocity factors and jetting factors of polycrystalline tin are all smaller than that of single crystalline tin at low impact velocity.However,with the increase of impact pressure,the influence of different grain orientation,grain boundary and other defects on the jetting process decreases,and the jetting results of polycrystal and single crystal tend to be the same.