title: Micromechanics of sea ice frictional slip from test basin scale experiments.
abstract: 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 σnis the normal stress) and n = 26/27, with a fractal asperity distribution, where the frictional shear stress, τ = ffractalTmlws, where ffractalis the fractal asperity height distribution, Tmlis the shear strength for frictional melting and lubrication and wsis 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'.
authors.affiliation: Rock and Ice Physics Laboratory, Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, UK p.sammonds@ucl.ac.uk.
authors.forename: Peter R
authors.identifier: http://orcid.org/0000-0003-3355-6761
authors.initials: PR
authors.lastname: Sammonds
authors.affiliation: Rock and Ice Physics Laboratory, Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, UK.|School of Marine Science and Engineering, Plymouth University, Drake Circus, Plymouth PL4 8AA, UK.
authors.forename: Daniel C
authors.initials: DC
authors.lastname: Hatton
authors.affiliation: Centre for Polar Observation and Modelling, Department of Meteorology, University of Reading, PO Box 243, Reading RG6 6BB, UK.
authors.forename: Daniel L
authors.initials: DL
authors.lastname: Feltham
keywords: micromechanics; scaling; sea ice friction