A model of the mechanics of shear-crack propagation in tearing for amorphous metals II. Kinetics of inhomogeneous flow

Abstract

This paper presents the dynamical mechanics of inhomogeneous plastic flow in the tear test, which can account for the kinetics of slip in thin sheets of a variety of amorphous alloys. Based on the newly derived formula for shear-crack propagation, the propagation rate of a shear-crack-tip with a single shear band in steady tearing is modelled in terms of tile mobility (v) of the front of a slip band: this is the fundamental flow unit in amorphous metals at available resolutions.

The thermodynamical motion of serrations in tearing is also modelled as a mechanic process and can be represented by a kinetic equation, v = A exp (-H/kT). The thermodynamical flow in amorphous alloys of various compositions is investigated in terms of the proposed mechanics. All of the amorphous alloys studied display serrated flow and obey the above kinetic equation. The activation energies (H) for onset of serrations in amorphous Pd₇₈Cu₆Si₁₆, Ni₇₀Fe₈Si₁₀B₁₂ and Co₇₈Si₁₀B₁₀, alloys arc 0.35, 0.40 and 0.48 eV respectively. The pre-exponential factor (A) is also a material parameter which is strongly dependent on the alloy composition.