Abstract
In order to elucidate the mechanism of deformation and fracture of microcomponents, numerical simulations are conducted for a nanoscopic wire and film of nickel without lattice defects on the basis of a molecular dynamics using the EAM(embedded atom method) potential. A bulk of nickel is also treated by applying a periodic boundary condition for comparison. These materials are subjected to a tensile strain along the[001]direction of the fcc(face-centered cubic) lattice. Here, the transverse stresses in the bulk material are kept at zero during tension. The yielding is brought about by the crystallographic slips on the(111)planes and there is little difference in the yield stress among the wire, film and bulk. The slips continue to take place on multiple(111)planes and the plastic deformation leads to ductile fracture. Next, the displacement in the transverse direction on the cell boundaries of the bulk is fixed in order to investigate the effect of constraint. It shows brittle fracture due to cleavage cracking. This implies that the constraint, which may be introduced by local inhomogeneity of the material, brings about early crack nucleation and reduces the ductility of materials without lattice imperfection.
