Shear strength of metals under uniaxial deformation and pure shear

Abstract

Abstract. In this paper, we investigate the dynamic shear strength of perfect monocrystalline metals using the molecular dynamics simulation. Three types of deformation (single shear, uniaxial compression and tension) are investigated for five metals of different crystallographic systems (fcc, bcc and hcp). A strong dependence of the calculated shear strength on the deformation type is observed. In the case of bcc (iron) and hcp (titanium) metals, the maximal shear strength is achieved at the uniaxial compression, while the minimal shear strength is observed at the uniaxial tension. In the case of fcc metals (aluminum, copper, nickel) the largest strength is achieved at the pure shear, the lowest strength is obtained at the uniaxial compression. IntroductionMechanical properties of materials considerably depend on the defects substructure. Dislocations consist one of the main types of defects determining the material plasticity and shear strength. A large number of dislocations usually exist in material in the initial state before deformation; motion and multiplication of these pre-existing dislocations provide the plastic relaxation in quasi-stationary conditions, as well as at dynamic deformation with moderate strain rates (up to about 10 8 s −1 ). At the same time, increasing of the strain rate or decreasing of volume of the deformed area leads to a dislocation starvation, which means that the density of pre-existing dislocation becomes insufficient for providing the plastic relaxation. The first situation takes place, for instance, at ultra-fast intensive laser irradiation of thin foils [1]; the second situation takes place at nanoindentation. A homogeneous nucleation of dislocations [2] determines the shear strength of material in these conditions; the crystal can be treated as a perfect one. Therefore, calculation of shear strength of perfect crystals has a sense.Molecular dynamics (MD) simulations [3] for iron single crystal (bcc lattice) had shown that under uniaxial compression the lattice withstand the shear stress, at least up to 15 GPa, while under uniaxial tension the shear strength is much less. In order to verify this fact and identify the dependence of the critical shear stress on the lattice type and the type of deformation, in present paper we carry out the MD simulations of uniaxial compression and tension and pure shear for five metals with different crystal lattice; bcc (iron), hcp (titanium) and fcc metals (aluminum, copper, nickel) are considered.

Molecular dynamics simulation studies on the plastic behaviors of an iron nanowire under torsion

“…As far as we are concerned, it has been used to study the motion of dislocation for Fe in MD simulations widely. [10][11][12]27,28 The simulation model was a cylindrical nanowire with a length of 15 nm and a radius of 5 nm, in total comprising 100 590, 101 288 and 100 828 atoms in h100i, h110i and h111i orientations, respectively. When there was a twist GB, the nanowires was divided into two equal parts by the GB.…”