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Title: Evolution of shear banding flows in metallic glasses characterized by molecular dynamics

Abstract

To reveal the evolution of shear banding flows, one-dimensional nanostructure metallic glass composites have been studied with molecular dynamics. The inherent size determines the initial thickness of shear bands, and the subsequent broadening can be restricted to some extent. The vortex-like flows evoke the atomic motion perpendicular to the shear plane, which accelerates the interatomic diffusion. The reduction of local strain rate causes the flow softening for monolithic Cu-Zr glass, but the participation of Cu-atoms in the shear banding flow gradually leads to the shear hardening for the composites.

Authors:
 [1];  [2]
  1. Shanghai Institute of Space Power-Sources, 2965 Dongchuan Rd., Shanghai 200245 (China)
  2. School of Materials Science and Engineering, Shanghai Jiao Tong University, 800 Dongchuan Rd., Shanghai 200240 (China)
Publication Date:
OSTI Identifier:
22596813
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 119; Journal Issue: 23; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ATOMS; COPPER; DIFFUSION; GLASS; HARDENING; METALLIC GLASSES; MOLECULAR DYNAMICS METHOD; NANOSTRUCTURES; ONE-DIMENSIONAL CALCULATIONS; SHEAR; STRAIN RATE; STRAINS; THICKNESS; VORTICES; ZIRCONIUM

Citation Formats

Yao, Li, E-mail: yltiger@sjtu.edu.cn, and Luan, Yingwei. Evolution of shear banding flows in metallic glasses characterized by molecular dynamics. United States: N. p., 2016. Web. doi:10.1063/1.4953816.
Yao, Li, E-mail: yltiger@sjtu.edu.cn, & Luan, Yingwei. Evolution of shear banding flows in metallic glasses characterized by molecular dynamics. United States. doi:10.1063/1.4953816.
Yao, Li, E-mail: yltiger@sjtu.edu.cn, and Luan, Yingwei. 2016. "Evolution of shear banding flows in metallic glasses characterized by molecular dynamics". United States. doi:10.1063/1.4953816.
@article{osti_22596813,
title = {Evolution of shear banding flows in metallic glasses characterized by molecular dynamics},
author = {Yao, Li, E-mail: yltiger@sjtu.edu.cn and Luan, Yingwei},
abstractNote = {To reveal the evolution of shear banding flows, one-dimensional nanostructure metallic glass composites have been studied with molecular dynamics. The inherent size determines the initial thickness of shear bands, and the subsequent broadening can be restricted to some extent. The vortex-like flows evoke the atomic motion perpendicular to the shear plane, which accelerates the interatomic diffusion. The reduction of local strain rate causes the flow softening for monolithic Cu-Zr glass, but the participation of Cu-atoms in the shear banding flow gradually leads to the shear hardening for the composites.},
doi = {10.1063/1.4953816},
journal = {Journal of Applied Physics},
number = 23,
volume = 119,
place = {United States},
year = 2016,
month = 6
}
  • Strain-induced hardening and annealing-induced softening are typical in crystalline metals. Bulk metallic glasses (BMG) exhibit the opposite behavior, namely, strain-induced softening and annealing-induced hardening. In addition, reversible softening-hardening-softening occurs in a BMG subjected to a three-step deformation-annealing-deformation process. The hardness changes after deformation and annealing can be correlated with the shear band patterns around/underneath Vickers indents. Shear bands produced during indentation of as-cast BMG are semicircular and radial, consistent with the stress distribution beneath the indenter. In contrast, the shear bands in the pre-strained BMG are irregular and convoluted, and appear to be a mixture of the shear bands producedmore » during the prior compression and those in the as-cast BMG. After annealing, the shear bands tend to recover their semicircular and radial shapes consistent with the annealing-induced hardening.« less
  • In this study, we demonstrated that the failure of BMGs results from sudden temperature rise within shear band. Using a shear-transformation-zone model, we successfully calculated the temperature within a shear band and found it consistent with the observation from an in-situ infrared thermographic system. The instantaneous temperature within a shear band (Ts) at fracture agrees remarkably well with the glass transition temperature (Tg), providing a new criterion to determine the strength of BMGs from their Tg. This agreement also discloses the fact that catastrophic failure of BMG is caused by the sudden drop in viscosity inside the shear band whenmore » Ts approaches Tg.« less
  • Nonequilibrium molecular dynamics simulations have been performed in order to compare the characteristics of planar Couette, planar elongation, uniaxial stretching, and biaxial stretching flows in simple fluids at different strain rates. After deriving the periodic boundary conditions for general flow fields and introducing some methodological improvements for elongation flow calculations we simulated the combination of shear and shear-free flows as well. We found that even at high strain rates where simple fluids exhibit strong non-Newtonian behavior (shear-thinning) it is a reasonable approximation to consider the two planar flows to be rotationally equivalent. This is because in planar Couette flow themore » in-plane normal stress difference of simple fluids is approximately zero even far from equilibrium. Similarly to planar Couette flow, the trace of the pressure tensor and the internal energy vary approximately as function of the 3/2 power of the strain rate in shear free flows. However, the individual diagonal elements of elongation flow pressure tensors deviate considerably from this approximation. In the extension direction the pressure seems to have a minimum in terms of the strain rate in every shear-free flow. We have discussed the implications of these results. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.« less
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