Examining Whether Normal Stress Affects Deformation Twinning

It is demonstrated for the first time by common tension/compression tests that the normal stress on twinning planes has an important effect on the twinning mechanism of some face-centered cubic metals. Specifically, a positive normal stress inhibits twinning and vice versa. Based on the results of quasi-in-situ tension, we proposed a new twinning criterion considering the normal stress effect, which can well interpret the twinning appearance that taking shear stress only cannot explain. Molecular statics simulations on the generalized stacking fault energy reveal the possible twinning mechanism for this effect. This finding provides a new interpretation for the twinning behavior in face-centered cubic metals.