Dynamics of a grain-scale intruder in a two-dimensional granular medium with and without basal friction

Abstract

We report on a series of experiments in which a grain-sized intruder is pulled by a spring through a 2D granular material comprised of photoelastic disks in a Couette geometry. We study the intruder dynamics as a function of packing fraction for two types of supporting substrates: a frictional glass plate and a layer of water for which basal friction forces are negligible. We observe two dynamical regimes: intermittent flow, in which the intruder moves freely most of the time but occasionally gets stuck, and stick-slip dynamics, in which the intruder advances via a sequence of distinct, rapid events. When basal friction is present, we observe a smooth crossover between the two regimes as a function of packing fraction, and we find that reducing the interparticle friction coefficient causes the stick-slip regime to shift to higher packing fractions. When basal friction is eliminated, we observe intermittent flow at all accessible packing fractions. For all cases, we present results for the statistics of stick events, the intruder velocity, and the force exerted on the intruder by the grains. Our results indicate the qualitative importance of basal friction at high packing fractions and suggest a possible connection between intruder dynamics in a static material and clogging dynamics in granular flows.

Intruder in a two-dimensional granular system: Effects of dynamic and static basal friction on stick-slip and clogging dynamics

“…In all cases, the dynamics is affected by the packing fraction and the strength of the driving mechanism, whether the intruder is driven at a constant velocity, by a constant force, or by a continually loading spring. An experiment on intruder dynamics in a 2D Couette geometry showed that friction between the particles and the supporting substrate (basal friction) also has a strong effect [15], as had previously been observed only in the context of quasistatic shear-jamming [16].…”

“…The packing fractions used for intruder does get stuck for a short period and then slips. This behavior is reminiscent of clogging of grains that flow through a restricted aperture; we refer to it as intermittent flow dynamics [15]. φ , for the frictional and the frictionless base.…”

“…Inspired by a recent experimental finding on the dynamics of an intruder the size of a single grain dragged though a two-dimensional granular system [15], we have developed numerical simulations that allow us to deepen our understanding of the effect of basal friction. Experimentally, it has been observed that the intruder can flow rather smoothly with occasional short sticks (intermittent flow regime) or show a fully developed stick-slip dynamics.…”

“…In the present work, we develop numerical simulations and validate them against the experimental findings in [15] with the aim of elucidating the influence of basal friction on the dynamics of an intruder moving through a granular medium, which is important for understanding the role of basal friction in supporting force-bearing clusters of grains subjected to a point load. We use numerical simulations to extend our study to parameter regimes that are difficult to access in the laboratory.…”

“…Negative forces are not present in the simulations due to the modeling of the torque spring as incapable of sustaining tension. In experiments, negative forces are only measured if the spring completely decompresses and the intruder rebounds due to a collision within the central axis (see Ref [15]. for more details).…”