A Coupled Molecular Dynamics/Coarse-Grained-Particle Method for Dynamic Simulation of Crack Growth at Finite Temperatures

Abstract

A hybrid molecular dynamics/coarse-grained-particle (MD-CGP) method is proposed for dynamic simulation of crack growth at finite temperatures. In the present method, the MD method is applied for the non-linear elastic region such as the crack tip and dislocation core, while the CGP method is applied for the surrounding linear elastic region. For coupling the atomistic and coarse regions, extra atoms and particles are placed, respectively, beyond the interface of the atomistic and coarse systems. They move according to the Langevin-type equation. The dissipation term in the Langevin-type equation contains the velocity difference between the atomistic and coarse systems. Hence, the coupling is achieved through the damped oscillation of the difference between the two systems. It is shown in a one-dimensional simulation that the present hybrid method achieves the non-reflecting boundary condition at the interface for the entire wavenumber range at finite temperatures. Two-dimensional crack growth simulations are performed using both the present hybrid MD-CGP method and full MD method for accuracy check. In the hybrid simulation, the location of the atomistic region shifts to follow the moving crack tip. In spite of such drastic operations, the results obtained by the present hybrid simulation agree very well with those by the full MD simulation. The hybrid MD-CGP method allows us to simulate very large systems without losing atomistic information at the singular point and non-linear region, with much lesser degrees of freedom than required for the full MD method.