Shear-Jammed, Fragile, and Steady States in Homogeneously Strained Granular Materials

Abstract

We study the jamming phase diagram of sheared granular material using a novel Couette shear set-up with multi-ring bottom. The set-up uses small basal friction forces to apply a volumeconserving linear shear with no shear band to a granular system composed of frictional photoelastic discs. The set-up can generate arbitrarily large shear strain due to its circular geometry, and the shear direction can be reversed, allowing us to measure a feature that distinguishes shearjammed from fragile states. We report systematic measurements of the stress, strain and contact network structure at phase boundaries that have been difficult to access by traditional experimental techniques, including the yield stress curve and the jamming curve close to φSJ ≈ 0.74, the smallest packing fraction supporting a shear-jammed state. We observe fragile states created under large shear strain over a range of φ < φSJ . We also find a transition in the character of the quasi-static steady flow centered around φSJ on the yield curve as a function of packing fraction. Near φSJ , the average contact number, fabric anisotropy, and non-rattler fraction all show a change of slope. Above φF ≈ 0.7 the steady flow shows measurable deviations from the basal linear shear profile, and above φc ≈ 0.78 the flow is localized in a shear band.

Sheared Amorphous Packings Display Two Separate Particle Transport Mechanisms

“…This suggests that D 1 no longer exists when the system approaches the density at which no or little shear is required to induce a finite pressure, signifying that all particles are sterically hindered. Note that D 1 changes character already at packing fractions (∼0.74) far below the random close packing limit, which coincides with the lowest ϕ needed for shear induced jamming to occur [3,13]. We can see this by probing the density dependent difference between MSD corr and D 2 min , as shown in Fig.…”

“…This directional transport, from now on defined as D 1 , occurs before the emergence of dilatancy-induced Reynolds pressure yet disappears in the random close packing limit. Moreover, the onset of D 1 emerges at larger ϕ for lower particle friction coefficients, which hints at its relevance for shear jamming phenomena, which display similar trends [3,13]. Interestingly, D 1 survives cyclic shear over many different cycles, converges to limit cycle behavior and displays strain dependence in its response to cyclic driving, making D 1 of interest as metric to capture the dynamics of memory formation in amorphous packings [7,12,15,[31][32][33][34][35][36].…”

“…These mechanical nontrivialities are most pronounced when a packing of particles is almost but not entirely rigid, as set by the particle volume fraction. Around this volume fraction, shear has the ability to "jam" or rigidify disordered packings [2,13]. The underpinnings of the mechanism are still under intense debate [14][15][16][17][18][19].…”

Soft-grain compression: Beyond the jamming point

“…The jamming transition have been widely studied over the past two decades [10,20,24,25,33] and observing it is not the main purpose of this paper. Still to validate the experimental method that we present and even if our system is not large enough for a proper study of this transition, the hyperelastic particle systems have been prepared loose enough to observed this transition point during the compression process.…”

“…Wound healing [1], cell monolayer growth [2,3], embryo developing [4,5], cancer invasion [6,7], squeezed foam [8][9][10][11], squeezed emulsion [12][13][14][15][16][17][18] and metal, plastic or ceramic powder sintering [19]; all these very different systems have the common point to be described as packings of discrete, deformable particles. Even if the jamming transition -the transition between a fluid-like and a solid-like behavior of the granular matter -of stiff or weakly deformable particles has been very well studied, theoretically [20][21][22][23], numerically [24][25][26][27][28][29] and experimentally [15,[30][31][32][33] during the past decades, very few is known about the behavior of these soft granular systems at high packing fraction.…”