Figure 1

Top, sketch of Couette shear apparatus, not to scale. $R_0=19.2\mathrm{cm}$. Data are for small or medium shearing wheels, where $R_i=6.7\mathrm{cm}/5.3\mathrm{cm}$. Particles are either circular or pentagonal in cross section, and have dimensions between 0.7 cm and 0.9 cm. Bottom: Data for the mean stress in a segment of a 2D granular Couette experiment containing roughly 200 particles vs shear $\dot{\gamma }$. Data (normalized by ${\sigma }_{\mathrm{dc}}\simeq 4.11\mathrm{N}{\mathrm{m}}^{-1}$) are for different packing fractions $\varphi$ relative to the critical packing fraction, ${\varphi }_c$, where stresses fall to zero. Symbols are: circles: $\varphi -{\varphi }_c=0.0012$, squares: $\varphi -{\varphi }_c=0.0091$, diamonds: $\varphi -{\varphi }_c=0.0152$, upward pointing triangles: $\varphi -{\varphi }_c=0.0189$, left-pointing triangles: circles: $\varphi -{\varphi }_c=0.0226$. We also consider other data (below) from experiments by Hartley and Behringer [11].Reuse & Permissions

Figure 2

Stress time series for several $\dot{\gamma }$ (mHz) for the smaller $R_i$.Reuse & Permissions

Figure 3

Blow up of time series data for the stress at $\dot{\gamma }=0.0533\mathrm{mHz}$ showing stress fluctuations over 0.2 rotations of the inner shearing wheel. The data indicate the approximately linear loading up of force structures and their more rapid failure.Reuse & Permissions

Figure 4

Fits (solid lines) to Eq. (18) of experimental data for $\Delta \sigma$ at $\varphi -{\varphi }_c=0.01373$, and $\dot{\gamma }$’s of 0.066 mHz (circle), 0.6645 mHz (square) and 13.307 mHz (triangle). The fits yield ${\sigma }_0\simeq 2.0$, independent of $\dot{\gamma }$ and ${\sigma }_m^0/{\sigma }_0\simeq 1.58$, 1.82, 2.0 (lowest to the highest value of $\dot{\gamma }$).Reuse & Permissions