Grain comminution is commonly observed in numerous geological settings. To elucidate the role of grain comminution in dry granular friction, we sheared breakable halite (NaCl) grains using a ring-shear configuration at a constant slip rate under various normal stresses. We observed transient frictional behaviors: a constant regime exhibiting a high friction coefficient at small slip displacements, and a weakening regime showing a substantial decay in friction at large slip displacements. The characteristic slip lengths for both regimes decreased with normal stress and were characterized by similar exponents. Micro-X-ray tomography revealed the evolution of microstructure from distributed grain comminution to progressive shear localization for these two regimes. We propose that the filling processes of comminuted fine particles, during which fine particles saturate and then overflow the shear zone, define transient frictional behaviors. This study may hold significant implications for natural shear systems, given the ubiquity of comminution and localization phenomena.

中文翻译：

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剪切颗粒岩盐中粉碎诱导的瞬态摩擦行为


在许多地质环境中都普遍观察到颗粒粉碎。为了阐明晶粒粉碎在干颗粒摩擦中的作用，我们在各种法向应力下以恒定的滑移率使用环剪切配置剪切了易碎岩盐 （NaCl） 晶粒。我们观察到瞬态摩擦行为：恒定状态在小滑移位移下表现出高摩擦系数，而减弱状态在大滑移位移下表现出摩擦力的显着衰减。两种状态的特征滑移长度均随正常应力的增加而减小，并具有相似的指数特征。显微 X 射线断层扫描揭示了这两种状态的微观结构从分布式晶粒粉碎到渐进剪切定位的演变。我们提出，粉碎的细颗粒的填充过程，在此过程中，细颗粒饱和，然后溢出剪切区，定义了瞬态摩擦行为。鉴于粉碎和局域现象的普遍存在，这项研究可能对自然剪切系统具有重要意义。