Plastic deformation at dynamic compaction of aluminum nanopowder: Molecular dynamics simulations and mechanical model

A mechanical model of a metal nanopowder compaction is proposed. It takes into account the change in the shape of nanoparticles during mutual indentation, the action of surface tension, elastic stresses and plastic deformation of particles. The plastic deformation is the key point of compaction; the dislocation approach is used to incorporate the plasticity into the model. The model considers the stage of free relaxation, when the nanoparticles are mutually attracted due to the surface tension and mutually repulsed due to the elastic stresses, and the stage of compaction, when the interplay between elastic deformation and plasticity defines the mechanical response of the powder. The model provides a kinetic form of the constitutive equations for nanopowder and is intended for use in macroscopic modeling of the shock-wave processes in the calculation of installations for dynamic compaction of nanopowders to describe the local mechanical reaction and estimate the degree of compaction in each finite element. Molecular dynamics (MD) simulations of the dynamic compaction of Al nanopowders with particle diameters in the range of 6-30 nm are carried out. Comparison with the results of MD shows that the proposed model adequately describes both the relaxation stage and the powder compression stage. The effects of temperature, strain rate and nanoparticles piling are considered.