Kothari Konik R, Elbanna Ahmed E
Mechanical Engineering Department, University of Illinois, Urbana-Champaign, Illinois 61801, USA.
Civil and Environmental Engineering Department, University of Illinois, Urbana-Champaign, Illinois 61801, USA.
Phys Rev E. 2017 Feb;95(2-1):022901. doi: 10.1103/PhysRevE.95.022901. Epub 2017 Feb 2.
Shear banding and stick-slip instabilities have been long observed in sheared granular materials. Yet, their microscopic underpinnings, interdependencies, and variability under different loading conditions have not been fully explored. Here we use a nonequilibrium thermodynamics model, the Shear Transformation Zone theory, to investigate the dynamics of strain localization and its connection to stability of sliding in sheared, dry, granular materials. We consider frictional and frictionless grains as well as the presence and absence of acoustic vibrations. Our results suggest that at low and intermediate strain rates, persistent shear bands develop only in the absence of vibrations. Vibrations tend to fluidize the granular network and delocalize slip at these rates. Stick-slip is observed only for frictional grains, and it is confined to the shear band. At high strain rates, stick-slip disappears and the different systems exhibit similar stress-slip response. Changing the vibration intensity, duration or time of application alters the system response and may cause long-lasting rheological changes. We analyze these observations in terms of possible transitions between rate strengthening and rate weakening response facilitated by a competition between shear-induced dilation and vibration-induced compaction. We discuss the implications of our results on dynamic triggering, quiescence, and strength evolution in gouge-filled fault zones.
在剪切颗粒材料中，剪切带和粘滑不稳定性早已被观察到。然而，它们的微观基础、相互依存关系以及在不同加载条件下的变异性尚未得到充分探索。在此，我们使用一种非平衡热力学模型——剪切转变区理论，来研究应变局部化的动力学及其与剪切干燥颗粒材料中滑动稳定性的联系。我们考虑了有摩擦和无摩擦的颗粒，以及有无声振动的情况。我们的结果表明，在低应变率和中等应变率下，持续的剪切带仅在无振动时形成。在这些应变率下，振动往往会使颗粒网络流化并使滑动非局部化。仅在有摩擦的颗粒中观察到粘滑现象，且其局限于剪切带。在高应变率下，粘滑消失，不同系统呈现出相似的应力 - 滑动响应。改变振动强度、持续时间或施加时间会改变系统响应，并可能导致持久的流变学变化。我们根据剪切诱导膨胀和振动诱导压实之间的竞争所促成的速率强化和速率弱化响应之间可能的转变来分析这些观察结果。我们讨论了我们的结果对充填断层泥的断层带中的动态触发、静止状态和强度演化的影响。
