Defect sensitivity of single-crystal nano-sized Cu beams

Molecular dynamics simulations of nano-sized beams with square cross sections of single-crystal Cu, solid as well as holding defects and loaded in displacement controlled tension until rupture have been performed. The defects are either edge crack-like or through-the-thickness voids. Three different cross section sizes and two different crystallographic orientations have been investigated. As expected, both geometry and crystal orientation influence the mechanical behavior. The strain at plastic initiation was, however, found almost independent of cross section size at given geometry and crystal orientation. Not surprisingly, the presence of defects lowers the strain at both plastic initiation and at rupture. More surprising is that embedded through-the-thickness voids under some circumstances might close to heal the beam cross section. The healing process seems to strengthen the beam and delay the final rupture. This applies for thin enough beams, allowing strong enough interatomic forces over the void, assisted by pertinent slip events.