From Schrödinger's Equation to the Rolling Mill: Joining Complex Process at the Micro and Meso Scales to Predict Onset Twinning Stress

Duane Johnson, Professor of Materials Science and Engineering and Bliss Faculty Scholar University of Illinois Urbana-Champaign.

Deformation twinning is observed in numerous engineering, chemical, and geological materials. Yet, unlike for shearing, there is no fundamental yield-stress criterion for twinning. We resolve this long-standing issue by integrating well-established concepts (dislocation mechanics and generalized planar fault energy surfaces that can be calculated directly from ab initio density functional methods) into a single approach, which account for processes occurring at relevant length scales in face-centered-cubic (fcc) metals during nucleation, and establish a closed-form, parameter-free expression for true (observed) stress that is quantitative, explains why twinning occurs in some fcc metals and not others, and predicts a linear relation between stress and unstable twin energy (borne out with observed data) which reveals the physics of twinning.