Atomistic simulation study of the shear-band deformation mechanism in Mg-Cu metallic glasses

Abstract

We have simulated plastic deformation of a model Mg-Cu metallic glass in order to study shear banding. In uniaxial tension, we find a necking instability occurs rather than shear banding. We can force the latter to occur by deforming in plane strain, forbidding the change of length in one of the transverse directions. Furthermore, in most of the simulations a notch is used to initiate shear bands, which lie at a 45°angle to the tensile loading direction. The shear bands are characterized by the Falk and Langer local measure of plastic deformation D min 2 , averaged here over volumes containing many atoms. The D min 2 profile has a peak whose width is around 10 nm;this width is largely independent of the strain rate. Most of the simulations were, at least nominally, at 100 K, about T g / 3 for this system. The development of the shear bands takes a few tens of ps, once plastic flow has started, more or less independent of strain rate. The shear bands can also be characterized using a correlation function defined in terms of D min 2 , which, moreover, can detect incipient shear bands in cases where they do not fully form. By averaging the kinetic energy over small regions, the local temperature can be calculated, and this is seen to be higher in the shear bands by about 50-100 K. Increases in temperature appear to initiate from interactions of the shear bands with the free surfaces and with each other, and are delayed somewhat with respect to the localization of plastic flow itself. We observe a slight decrease in density, up to 1%, within the shear band, which is consistent with notions of increased free volume or disorder within a plastically deforming amorphous material.

Orientational glass in mixtures of elliptic and circular particles: Structural heterogeneities, rotational dynamics, and rheology

“…which is possible owing to the attractive part of the potential [44]. From the symmetry of the geometry, we also have σ xy s = 0.…”

“…We mention similar simulations in Refs. [30,44]. In the following figures, the x and y axes are in the horizontal and vertical directions, respectively.…”

Size-independent shear band formation in amorphous nanowires made from simulated casting

“…5,20,21 Nonetheless, cylindrical-shaped samples, which are most relevant to experiments, have shown nearly homogeneous flow until necking at high strains 22,23 and only exhibit shear bands upon the introduction of a surface notch. 24,25 The central question is whether the emergence of a shear band is a result of special dimensionality or sample geometry, and whether the absence of shear bands in cylindrical samples is due to the small sample size. One important issue that has so far been overlooked is the sample preparation procedure, as previous cylindrical-shaped samples were usually obtained by cutting from a bulk sample at a low temperature.…”

Temperature, Strain and Strain Rate Dependence of Serrated Flow in Bulk Metallic Glasses

“…14) Parameters such as the strain rate sensitivity (SRS), size of the activated volume in a STZ and potential energy of deformation have also been derived recently from computer simulations. [15][16][17][18] These results combined with Refs. 13 and 14 have provided a deeper understanding of the kinetics of STZs -information which is difficult to assess experimentally.…”