Mechanical and Civil Engineering Seminar

The plastic behavior of BCC single crystals is governed by screw dislocation glide on close-packed crystallographic planes. Screw dislocation motion occurs via thermally-activated nucleation and relaxation of so-called kink pairs on a periodic energy substrate known as the Peierls potential. A long standing puzzle regarding BCC plasticity has been the discrepancy between the measured values of the flow stress in tensile deformation tests and the calculated values of the Peierls stress at the atomistic scale. Here, we present a model that unifies both concepts and provides a justification for the differences in terms of the non-Schmid behavior displayed by BCC crystals. Our model consists of a crystal plasticity microstructural engine parameterized entirely using atomistic calculations, that includes full non-Schmid effects as well as a physically-consistent  flow rule constructed on the basis of thermally activated screw dislocation glide. We apply the methodology to yielding in tungsten and show that available experimental measurements can be explained and reproduced by accounting for these two very important features of BCC plasticity. The validated methodology is used to predict strength as a function of several state variables in W single crystals.