Tension–compression asymmetry in nanocrystalline Cu: High strain rate vs. quasi-static deformation

Large-scale molecular dynamics (MD) simulations are used to understand the yield behavior of nanocrystalline Ni and Cu with grain sizes ⩽10 nm at high strain rates. The calculated flow stress values at a strain rate of 109 s−1 suggest an asymmetry in the strength values in tension and compression with the nanocrystalline metal being stronger in compression than in tension. This tension–compression strength asymmetry is observed to decrease with a decrease in grain size of the nanocrystalline metal up to a grain size of 4 nm, after which, a further decrease in grain size results in an increase in the strength asymmetry. The effect of strain rate on the yield behavior of nanocrystalline metals as obtained from MD simulations is discussed and compared with that reported in the literature obtained by molecular statics simulations for quasi-static loading conditions.