Sammonds Peter R, Hatton Daniel C, Feltham Daniel L
Rock and Ice Physics Laboratory, Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, UK
Rock and Ice Physics Laboratory, Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, UK.
Philos Trans A Math Phys Eng Sci. 2017 Feb 13;375(2086). doi: 10.1098/rsta.2015.0354.
We have conducted a series of high-resolution friction experiments on large floating saline ice floes in an environmental test basin. In these experiments, a central ice floe was pushed between two other floes, sliding along two interfacial faults. The frictional motion was predominantly stick-slip. Shear stresses, normal stresses, local strains and slip displacement were measured along the sliding faults, and acoustic emissions were monitored. High-resolution measurements during a single stick-slip cycle at several positions along the fault allowed us to identify two phases of frictional slip: a nucleation phase, where a nucleation zone begins to slip before the rest of the fault, and a propagation phase when the entire fault is slipping. This is slip-weakening behaviour. We have therefore characterized what we consider to be a key deformation mechanism in Arctic Ocean dynamics. In order to understand the micromechanics of sea ice friction, we have employed a theoretical constitutive relation (i.e. an equation for shear stress in terms of temperature, normal load, acceleration, velocity and slip displacement) derived from the physics of asperity-asperity contact and sliding (Hatton et al. 2009 Phil. Mag. 89, 2771-2799 (doi:10.1080/14786430903113769)). We find that our experimental data conform reasonably with this frictional law once slip weakening is introduced. We find that the constitutive relation follows Archard's law rather than Amontons' law, with [Formula: see text] (where τ is the shear stress and σ is the normal stress) and n = 26/27, with a fractal asperity distribution, where the frictional shear stress, τ = f Tw, where f is the fractal asperity height distribution, T is the shear strength for frictional melting and lubrication and w is the slip weakening. We can therefore deduce that the interfacial faults failed in shear for these experimental conditions through processes of brittle failure of asperities in shear, and, at higher velocities, through frictional heating, localized surface melting and hydrodynamic lubrication.This article is part of the themed issue 'Microdynamics of ice'.
我们在一个环境试验池中对大型漂浮盐冰浮进行了一系列高分辨率摩擦实验。在这些实验中，一块中心浮冰被推挤在另外两块浮冰之间，沿着两条界面断层滑动。摩擦运动主要是粘滑运动。沿着滑动断层测量了剪应力、法向应力、局部应变和滑动位移，并监测了声发射。在沿着断层的几个位置进行的单个粘滑循环期间的高分辨率测量，使我们能够识别摩擦滑动的两个阶段：一个成核阶段，在此阶段成核区在断层的其余部分之前开始滑动；以及一个扩展阶段，此时整个断层都在滑动。这就是滑动弱化行为。因此，我们已经描述了我们认为是北冰洋动力学中的一个关键变形机制。为了理解海冰摩擦的微观力学，我们采用了一个从粗糙体 - 粗糙体接触和滑动物理学推导出来的理论本构关系（即一个关于剪应力与温度、法向载荷、加速度、速度和滑动位移的方程）（哈顿等人，《哲学杂志》89，2771 - 2799（doi:10.1080/14786430903113769））。我们发现，一旦引入滑动弱化，我们的实验数据与这个摩擦定律相当吻合。我们发现本构关系遵循阿查德定律而非阿蒙顿定律，其中[公式：见正文]（其中τ是剪应力，σ是法向应力）且n = 26 / 27，具有分形粗糙体分布，其中摩擦剪应力τ = fTw，其中f是分形粗糙体高度分布，T是摩擦熔化和润滑的抗剪强度，w是滑动弱化。因此我们可以推断，在这些实验条件下，界面断层通过粗糙体在剪切中的脆性破坏过程以及在较高速度下通过摩擦加热、局部表面熔化和流体动力润滑而在剪切中失效。本文是主题为“冰的微观动力学”的特刊的一部分
