Reversible–irreversible plasticity transition in twinned copper nanopillars

Abstract Through computer simulations, we show that plasticity in twinned copper nanopillars can be either reversible or irreversible depending on the applied stress state. Copper nanopillars, containing twinned crystals, are subjected to both compression and tension, and the ratio of the resolved shear ( σ R ) to the normal stress ( σ N ) , R, is adjusted through variation of the orientation of the twin boundary plane with respect to the loading axis. It is found that the yield locus on the σ R – σ N plane for twinned nanopillars is asymmetric with respect to the sign of R. For a 9 nm diameter copper nanopillar under compression, plastic deformation can be totally reversed when σ R is in the range 0.5 ⩽ σ R ⩽ 1 GPa , with a corresponding increase in the compressive normal stress, up to ≈2.5 GPa. It is shown that these conditions are achieved for axial strains