Molecular Dynamics Simulation Of Al Nanopowder Preparation By Exploding Wire

Metal powder is widely used as fuel in solid rocket propellant.Compared with micron metal powder,metal nano-powder can increase propellant burning rate,shorten ignition delay time,and decrease agglomeration combustion time,thus improve propellant combustion efficiency and combustion stability.Many countries in the world have carried out extensive research on the preparation of metal nano-powder and its application in high-energy condensation system.Electric explosion of metal wire is one of the most promising methods for the preparation of metal nano-powder due to its advantages of high energy utilization,high product activity and purity.Electric explosion of metal wire is an unbalanced development process under extreme conditions,and the dissociation mechanism of metal materials is not fully understood.In this paper,the phenomenon of wire electric explosions is studied,then the slow matched mode explosion of metal wire is simplified physically,and the molecular dynamics model of the electric explosion of wire under classical mechanics is established.We have done a series of simulations to study the wire explosion behavior of aluminum wire in vacuum,including the wire diameter,deposition energy,and energy deposition rate.We focus on the dissociation mechanism of metal materials under extreme conditions and the distribution characteristics such as size and temperature of the initial clusters.The EAM potential is employed for describing the interatomic interaction,and simulations are carried out by the LAMMPS program,and MATLAB is used for post-processing.Molecular dynamics method is used to calculate out aluminum isotherms near the critical point for the state analysis of explosive materials.First,the feasibility of the simplified model is verified.The formation and degradation of the foam-structure in underheated explosion was observed in the explosion simulations of aluminum wire with the heated coefficient of 0.45,which is an important stage in the formation of large particles in experiments.Although the size that the computer can simulate is much smaller than the diameter of the wire in the real wire electric explosion,the simulation results show that pressure,temperature,expanding rate,and morphology development are in good agreement with the experiments.This indicates that the simplification of wire explodosin in this paper is effective and feasible.The effect of diameter is to influence the explosion phenomenon by affecting the radial distribution and evolution time of thermodynamic parameters.The study on the transformation of deposited energy shows that,energy is not preferentially converted into internal energy of materials,but simultaneously into explosive kinetic energy.That even the deposited energy reaches or exceeds the sublimation energy of material,it cannot be completely vaporized the wire.The state changing trajectory at different energy deposition levels are calculated and the results show that the deposition energy density determines the state evolution path of metal material.With the increase of heated coefficient from 0.2 to 1.0,the wire undergoes mechanical fragmentation,phase explosion,explosion under two mechanisms,and supercritical explosion in turn,and the particle size of the explosive product becomes smaller and the gasification rate increases.The effect of energy deposition rate on explosion is mainly carried out through surface processes.If the heating time is longer than the time of the rarefaction wave propagates to the center,the continuous material scattering on the surface replaces the phase explosion.If surface evaporation dominated the explosion,there would finally leave a residual liquid wire.It is of great value on the preparation technology optimization to study the dissociation mechanism of wire materials and the distribution characteristics of the initial paiticles in the electric explosion of metal wire.In addition,the smaller of the wire diameter,the stronger of the surface activity,so the effect of size effect should be taken into account when applied to experiments and productions.