Molecular dynamics simulation of plastic deformation in nano-sized plate: Atomic-scale super-elasticity and forming limit of pure copper single crystal

The forming process of nano-sized plate is investigated by using the molecular dynamics (MD) method as a microscopic theoretical analysis. Square-shaped plate models composed of single-crystal copper atoms with thicknesses of several nanometers (2–16 times the lattice constant of the face-centered cubic (FCC) lattice) are clamped by other rigid plates, and a rigid plug with cylindrical shape is pushing into the plate at a constant velocity. The forming limit diagram (FLD) obtained from atomic strains is successfully assessed. It is understood that dislocations and their motions play a crucial role in plastic deformation. The types and distribution of dislocations are compared for models with different crystal orientations of the surface, that is, {100}, {110} and {111} planes. The unloading process following the stoppage of the plug just before any breakage in the plate is also conducted. In unloading, extraordinary recovery of deformation close to 100 percent can be expected, particularly in very thin plate. It is concluded that the formability is the largest in {100} plane’s case and a thicker plate accompanies lower spring-back. It is also found in fracture behavior that initiation of defects in the plate occurs around icosahedral (ICO) structure, which does not match the FCC crystal nor the slip of dislocations.