Publication 26-CNA-005
Averaging Molecular Dynamics Simulations to Study the Slow-strain Rate Behavior of Metals
Sarthok Kumar Baruah
Department of Applied Mechanics
Indian Institute of Technology Delhi
New Delhi, India
amy237541@am.iitd.ac.in
Sabyasachi Chatterjee
Department of Applied Mechanics
Indian Institute of Technology Delhi
New Delhi, India
sabyasachi@am.iitd.ac.in
Amit Acharya
Dept. of Civil & Environmental Engineering
Center for Nonlinear Analysis
Carnegie Mellon University
Pittsburgh, PA 15213
acharyaamit@cmu.edu
Gerald J. Wang
Department of Civil and Environmental Engineering
Carnegie Mellon University
Pittsburgh, PA 15213
gjwang@cmu.edu
Abstract: The application of molecular dynamics (MD) simulations to quasi-static loading is severely limited by the large separation between atomic vibration timescales and experimentally relevant deformation rates. In this work, we employ the Practical Time Averaging (PTA) framework to overcome this limitation and enable atomistic simulations of crystalline solids under quasi-static loading conditions. PTA exploits the intrinsic separation of timescales by defining slow variables as time-averaged observables of the fast atomistic dynamics and their evolution in the slow loading timescale, thereby avoiding explicit integration of the fast dynamics.
Using this approach, we simulate uniaxial deformation, in both tension and compression, of (4 to 20) nanometer sized cubic specimens of face-centered cubic Aluminum nanocrystals and applied strain rates approaching quasi-static conditions (10
-4 s-1 - 10
-3 s-1). We define slow variables as the averaged kinetic energy, potential energy and normal stress in the loading direction, and show their evolution in the slow time scale. The stress-strain curves show yield close to the theoretical yield stress for homogeneous nucleation, followed by successive load drops and rise, caused due to dislocation nucleation, motion and exit from free surfaces. The "smaller is harder" effect is evident from the stress-strain response as well as from the variation of yield stress with the sample size. The serrations in the response are more pronounced for smaller samples. The effects of applied strain rate and initial temperature are studied. The PTA framework enables simulations at strain rates several orders of magnitude lower than those accessible to conventional MD, demonstrating significant speedup in computer time, while retaining full atomistic resolution.
Get the paper in its entirety as 26-CNA-005.pdf
« Back to CNA Publications
