Molecular dynamics simulation of nanostructure formation in copper foil under laser shock forming

Abstract

The microstructure evolution of polycrystal copper under high strain rate loading is studied via the molecular dynamics simulation, and the formation of nanostructures in copper foil under laser shock forming is revealed. Deformation is dominated by dislocations in the early stage. Partial dislocations are emitted from grain boundaries. Then, they pass through grains and are absorbed by the opposite grain boundaries. When stress is concentrated, second slip, cross slip, and slip system alternation occur. Different dislocation motions form sub-grain boundaries, and sub-grains transform into refined grains via dynamic recrystallization. In our previous experiment, the effect of dislocations on grain refinement was neglected. Deformation twinning, including the nano-twin bundles observed in the experiment, appears in the late stages of deformation. Twins are formed by a series of dislocation motions. Twins and dislocations collectively dominate plastic deformation and form a competing relationship, increasing the toughness and the strength of the material. High strain rate and large strain are vital to the formation of these nanostructures.