Accelerated molecular dynamics simulations for characterizing plastic deformation in crystalline materials with cracks

Molecular Dynamics (MD) simulations are often used for comprehending evolving deformation mechanisms in materials at the atomic scale and also for assessing continuum-scale material properties. A major limitation of conventional MD simulations is that very small MD time-scale (similar to fs), restrict the achievable strain-rates to be much higher (similar to 107 or higher) than experimentally observed rates, needed for continuum scale modeling, e.g. using crystal plasticity finite element methods. A strain-boost hyperdynamics method based accelerated MD tool is adopted and developed to overcome these limitations. This method biases the atomic system to make it evolve at much faster time-scales and achieve strainrates that are at least three order of magnitude smaller than the lowest strain-rate achievable in MD. The hyperdynamics algorithm is implemented in a parallel version of LAMMPS, and validated with conventional MD. It is then used to predict evolution of plastic state variables at lower strain-rates for a Nickel single crystal with an embedded atomistic crack. It is shown that at lower strain-rates, not only the evolution of plastic variables are different, but for some configurations there is a shift in the plastic deformation mechanism from twin dominated to dislocation dominated. (C) 2016 Elsevier B.V. All rights reserved.