The theoretical shear strength of bcc metals under superimposed normal stress

M. Černý and P. Šesták

Faculty of Mechanical Engineering, Brno University of Technology, Brno, Czech Republic.

 The influence of a stress applied perpendicularly to shear planes during homogeneous shear deformation of bcc crystal on the shear strength is important in many deformation processes. As an example, one can consider a nanoindentation process as a combination of shear and compressive deformations in the vicinity of an indentor. Previous studies on fcc metals suggested nearly linear increasing (decreasing) dependence of the theoretical shear strength on the normal compressive (tensile) loading. The aim of this study is to compare the former results for fcc metals with the recent data for bcc metals.
 Atomistic simulations of the shear deformation in bcc crystals are performed using first principles method based on pseudo-potentials and plane wave basis set.
 The bcc crystals are subjected to deformations in <111>{112} and <111>{110} shear systems and a special relaxation procedure is used to converge the normal stress to a preset constant level. The relaxation procedure is employed at any step of incrementally increasing shear deformation.