Yadav Shwetabh, Sagapuram Dinakar
Department of Industrial and Systems Engineering, Texas A&M University, College Station, TX, USA.
Department of Materials Science and Engineering, Texas A&M University, College Station, TX, USA.
Proc Math Phys Eng Sci. 2020 Feb;476(2234):20190519. doi: 10.1098/rspa.2019.0519. Epub 2020 Feb 19.
Shear banding is a plastic instability in large deformation of solids where the flow becomes concentrated in narrow layers, with broad implications in materials processing applications and dynamic failure of metals. Given the extremely small length and time scales involved, several challenges persist in studying the development of shear bands. Here, we present a new approach to study shear bands at low speeds using low melting point alloys. We use imaging to directly capture the essential features of shear banding, including transition from homogeneous to shear banded flow, band nucleation and propagation dynamics, and temporal evolution of the flow around a developing band. High-resolution, time-resolved measurements of the local displacement and velocity profiles during shear band growth are presented. The experiments are complemented by an analysis of the shear band growth as a Bingham fluid flow. It is shown that shear banding occurs only beyond a critical shear stress and is accompanied by a sharp drop in the viscosity by several orders of magnitude, analogous to the yielding transition in yield-stress fluids. Likewise, the displacement field around a nucleated band evolves in a manner that resembles boundary layer formation, with the band thickness scaling with time as a power law.
剪切带是固体大变形中的一种塑性失稳现象，此时流动集中在狭窄的层中，在材料加工应用和金属动态失效方面具有广泛影响。鉴于所涉及的长度和时间尺度极小，在研究剪切带的发展过程中仍存在若干挑战。在此，我们提出一种使用低熔点合金在低速下研究剪切带的新方法。我们利用成像直接捕捉剪切带的基本特征，包括从均匀流到剪切带流的转变、带核的形成和传播动力学，以及发展中的带周围流动的时间演化。本文给出了剪切带生长过程中局部位移和速度剖面的高分辨率、时间分辨测量结果。通过将剪切带生长分析为宾汉流体流动对实验进行补充。结果表明，剪切带仅在超过临界剪应力时出现，并伴随着粘度急剧下降几个数量级，这类似于屈服应力流体中的屈服转变。同样，成核带周围的位移场以类似于边界层形成的方式演化，带厚度随时间呈幂律缩放。
