Atomic-Scale Study of Plastic-Yield Criterion in Nanocrystalline Cu at High Strain Rates

Autor: Mohammed A. Zikry, Avinash M. Dongare, A. M. Rajendran, Bruce LaMattina, Donald W. Brenner
Rok vydání: 2009
Předmět:
Zdroj: Metallurgical and Materials Transactions A. 41:523-531
ISSN: 1543-1940
1073-5623
DOI: 10.1007/s11661-009-0113-x
Popis: Large-scale molecular dynamics (MD) simulations are used to understand the macroscopic yield behavior of nanocrystalline Cu with an average grain size of 6 nm at high strain rates. The MD simulations at strain rates varying from 109 s−1 to 8 × 109 s−1 suggest an asymmetry in the flow stress values in tension and compression, with the nanocrystalline metal being stronger in compression than in tension. The tension-compression strength asymmetry is very small at 109 s−1, but increases with increasing strain rate. The calculated yield stresses and flow stresses under combined biaxial loading conditions (X-Y) gives a locus of points that can be described with a traditional ellipse. An asymmetry parameter is introduced that allows for the incorporation of the small tension-compression asymmetry. The biaxial yield surface (X-Y) is calculated for different values of stress in the Z direction, the superposition of which gives a full three-dimensional (3-D) yield surface. The 3-D yield surface shows a cylinder that is symmetric around the hydrostatic axis. These results suggest that a von Mises-type yield criterion can be used to understand the macroscopic deformation behavior of nanocrystalline Cu with a grain size in the inverse Hall–Petch regime at high strain rates.
Databáze: OpenAIRE
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