Nonlinear effects of particle shape angularity in sheared granular media

Abstract

We analyze the effects of particle shape angularity on the macroscopic shear behavior and texture of granular packings simulated by means of the contact dynamics method. The particles are regular polygons with an increasing number of sides ranging from 3 (triangles) to 60. The packings are analyzed in the steady shear state in terms of their shear strength, packing fraction, connectivity, and fabric and force anisotropies, as functions of the angularity. An interesting finding is that the shear strength increases with angularity up to a maximum value and saturates as the particles become more angular (below six sides). In contrast, the packing fraction declines towards a constant value, so that the packings of more angular particles are looser but have higher shear strength. We show that the increase of the shear strength at low angularity is due to an increase of both contact and force anisotropies, and the saturation of the shear strength for higher angularities is a consequence of a rapid fall-off of the contact and normal force anisotropies compensated by an increase of the tangential force anisotropy. This transition reflects clearly the rather special geometrical properties of these highly angular shapes, implying that the stability of the packing relies strongly on the side-side contacts and the mobilization of friction forces.

Does modifying the particle size distribution of a granular material (i.e., material scalping) alters its shear strength?

“…The probability density function P(θ) of contact normals provides detailed statistical information about the fabric. It is π-periodic in the absence of an intrinsic polarity for n. At the lowest order, we have [14,15] …”

Bonded-cell model for particle fracture

“…The CD method is based on implicit time integration of velocities but requires an explicit determination of the contact network at the beginning of each time step [52,73]. The contact detection between two bodies consists in looking the portions of space they occupy.…”

Particle alignment and clustering in sheared granular materials composed of platy particles

“…For instance, packings of elongated [10][11][12]15] and nonconvex [20,21] particles have unusually high or low packing fractions, while the shear strength is observed to grow as the shape increasingly deviates from the disk or the sphere. The shear strength in packing of polyhedral particles increases with angularity and saturates at a maximum, whereas the packing fraction declines towards a plateau [16,19].…”

“…The contact networks resulting from various shapes appear to be highly complex and hardly amenable to simple statistical modeling. For example, face/face interactions are critical for polyhedra whereas interlocking of the particles is important in the case of non-convex shapes [15,21,16,18,19]. In the same way, nematic order appears in packings of elongated particles [10][11][12]9,15,18].…”

“…The grain shape considerably affects the quasi-static mechanical behavior of granular materials [4][5][6][7][8][9]14,33]. There is a multitude of potential particle morphologies and recently a wide range of nontrivial effects were -systematically -reported by means of discrete numerical simulations [10][11][12][13][14][15][16][17]19]. Indeed, one of the major interests of discrete approach is to make it possible to control precisely the shape of the particles with continuously-variables parameters.…”