Mechanical Behavior and Size Sensitivity of Nanocrystalline Nickel Wires Using Molecular Dynamics Simulation

The mechanisms of deformation and failure in face-centered cubic (FCC) nickel nanowires subjected to uniaxial tensile loading are investigated using molecular dynamics (MD) simulation, and the size effect on mechanical properties of FCC metal nanowires is studied. Simulation reveals that the surface free energy has great influence on the deformation and failure mechanism of metal nanowires. As a result of free surfaces and their reconstruction, the surface atoms depart from the perfect crystal lattice positions, leading to the appearance of nanocavities on the surfaces that are exposed to external load. The deformation process of nanowires undergoes expansion and connection of nanocavities from surface into inner lattices. Slip occurs during the deformation process, which is consistent with experimental phenomena. Elastic stiffness, yield, and fracture strength of nickel nanowires with various cross-sectional sizes are obtained, and the size effect on these mechanical properties is further analyzed. Based on numerical results, a set of quantitative prediction formulas are proposed, and they are capable of explaining the size sensitivity of nickel nanowires on the mechanical properties. Both the elastic modulus and yield strength of nickel nanowires are in a linear relationship with respect to the logarithm of their cross-sectional size, whereas the fracture strength exhibits an inverse relationship to the exponent of cross-sectional size of nickel nanowires. By using the MD simulation, the elastic modulus, yield strength, and fracture strength of a nickel nanowire in relationship to its cross-sectional size are well predicted, and they are in remarkable agreement with experimental and available numerical results. The present study demonstrates that the adopted MD simulation is capable of simulating the mechanical behavior of nanowires with respect to their geometrical size and providing numerical data that can be used to develop the empirical formulas on the effect of various physical and geometric parameters on their mechanical properties. DOI: 10.1061/(ASCE)AS.1943-5525.0000006. (C) 2011 American Society of Civil Engineers.