Approximate prediction of theoretical tensile strength of cubic crystals

M. Cerny and J. Pokluda, Faculty of Mechanical Engineering, Brno University of Technology, Brno, Czech republic

Uniaxial tensile tests belong to the easiest experimental strength measurements. Results of such 
experiments on whiskers as well as theoretical studies based on atomistic modelling suggested that
rupture of many crystals is related to reaching the shear strength in some convenient slip system.

This work presents a simple way how to estimate the uniaxial tensile strength 
based on calculations of the theoretical shear strength and its dependence on superimposed normal stress.
The atomistic simulations of the shear and tensile deformations in cubic crystals are performed using first principles computational code based on pseudo-potentials and plane wave basis set. The fcc (bcc) crystals are subjected to shear deformation in <112>{111} (<111>{112}) slip systems and special relaxation procedure controls the stress tensor.

Obtained dependence of the ideal shear strength on normal tensile stress seems to be almost linearly decreasing for all investigated crystals. Taking our results into account, the uniaxial tensile strength values in [100] direction were evaluated for selected cubic crystals.