Modeling the Dynamic Propagation of Shear Bands in Bulk Metallic Glasses

A model is developed for quantifying shear-band propagation in bulk metallic glasses. This model is written in terms of the stress, temperature, and band propagation speed. The model quantifies the shear-band length, width, and speed, as well as the direction of propagation and the magnitude of displacement across the band. Corresponding author: B.J. Edwards, [email protected] (865) 975-9596 The formation of shear bands in materials under an applied stress has been studied extensively over the past two decades; however, truly dynamic models of the propagation of these bands are still in the process of being developed. Recent efforts have made remarkable strides toward understanding this phenomenon, but continuum models that can describe the essential physics of shear band propagation are still largely unavailable. In the present work, a macroscopic model is presented for describing the propagation and dissipation of shear bands in bulk metallic glasses (BMGs). This model is written in terms of three relevant variable fields, the stress tensor, σ (Pa), the absolute temperature, T (K), and the flux (propagation speed) of the free volume, φ (m/s), as well as experimentally determined parameters, such as the mass density, heat capacity, conductivity, etc. Finite-element (FE) calculations of the resulting model equations allow the estimation of the characteristic features of the shear band, such as the width, length, and speed of propagation, as well as the temperature, stress, and displacement profiles along the band length. In a recent article [1], the evolution of shear bands in a Zr-based BMG was observed in-situ during tensile loading via thermographic imaging with a high-speed infrared (IR) camera. In these experiments [1], Zr-based BMG Zr52.5Cu17.9Ni14.6Al10.0Ti5.0 samples were subjected to tensile loading in a load-control mode with a loading rate of 44.5 N/s. An IR camera recorded thermographic images of the sample surface at a frame rate of 725 Hz, which amounted to one camera frame every 0.00138 s. After a linear stress-strain regime at low loads (with Young’s modulus, , of about 100 GPa [2,3]), plastic deformation began and the onset of shear-band generation occurred. The heat generated during the shear deformation along the band was measured 0 E