Evidence for Bingham plastic boundary layers in shear banding of metals

We study material flow in the vicinity of single shear bands in high strain-rate (10(4) -10(5) per second) deformation of metals. Shear band plastic flow, in three different materials, is shown to resemble unsteady planar Couette flow (Stokes first problem) of a Bingham fluid. Equivalent shear band viscosities and yield stresses are obtained, with the former similar to liquid metal viscosities and the latter being similar to 0.5 times the band nucleation stress. Reynolds and Bingham numbers, computed based on the shear band displacement measurements, are suggestive of boundary layer formation, consistent with the severe localization of deformation within shear bands. (C) 2018 Elsevier Ltd. All rights reserved.