Molecular Dynamics Simulation Of The Effect Of Nano - Holes On Mechanical Properties

Nanovoids can result from such processes as incipient spallation and radiation damage, on the other hand nanofoam metal have some special characteristics due to its unique structures, that render them promising applications as advanced mechanical or function materials. Here we take aluminum as an example for its wide application to investigate the mechanical properties of metals configured with nanovoids with molecular dynamics simulation. With the embedded atom method potential employed, the result of the molecular dynamics simulation of monocrystal aluminum with nanovoids subjected to uniaxial compression along different lattice orientations in strain rate of 2×109m=1 was analyzed.1. It is confirmed that the dominating mechanism of void growth and plastic deformation is the dislocation nucleation, emission and slip in the lattice. As the stress reach the critical value the dislocation emission happens, then dislocations move into the lattice, resulting in a dislocation forest formed by dislocation accumulation.2. There are twelve{111}(110) slip systems in face-center cubic crystals and can be partially activated when subjected to uniaxial deformation by resolved shear stress resulting in the dislocation emission and slip from the void surface and the plastic deformation of metal. There is no evident correlation between the onset strains of dislocation emission and the selected three orientations. Thus there is an obvious anisotropy of yield stresses of the nanovoided models.3. The measurement of dislocation velocities reveals that the emitted dislocations move subsonically in the lattice when subjected to uniaxial loading of strain rates in such magnitude of ～109m-1. When subjected to [100] and [111] compression the dislocation emitted in a radiational pattern thus the velocity is as stable as a constant. While when the loading is in [110] direction, the dislocations move in variable speed because of the formation of dislocation locks in the conjunction of slip planes.4. No twinning was found in the simulation. Prismatic dislocation emission was observed when subjected to unaxial compression along [110] crystallographic orientation probably because of sufficient space along the specific direction parallel to the loading orientation.5. The dislocation accumulation of nanoporous models can be separated according to the dislocation density evolution in the initial stage of plastic deformation into a piecewise linear procedure because of the generation of trail partials. When subjected to [100] and [111] compression mobile dislocation densities are close to which of the total, on the other hand the density of mobile dislocations is about one magnitude lower than the total dislocation when the loading is in [110] crystallographic orientation.6. Taking the surface effect of nanovoids into consideration, a correction of critical stress of dislocation emission onset is given by introducing the ledge effect of the nanovoid surfaces. The given equation performances a good accordance to the atomistic simulation result can give a good prediction of the yield behavior of materials with nanovoids even in radius lower than one lattice constant.