Influence of superimposed normal stress on shear strength of perfect bcc crystals

The influence of a stress applied normally to shear planes on the theoretical shear strength of bcc crystals was studied for the 〈 1 1 1 〉 { 1 1 2 } shear system in both the twinning and the anti-twinning shear mode. The applied computational procedure employed first principles code working in the framework of density functional theory. The modeled deformation of crystal lattice is represented by a uniform distortion of the primitive cell which is subjected to a superposition of shear and normal stresses. The theoretical shear strength was found to be a decreasing (increasing) function of the applied tensile (compressive) normal stress in most studied cases.