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

摘要

We study the jamming phase diagram of sheared granular material using a novel Couette shear setup with a multiring bottom. The setup uses small basal friction forces to apply a volume-conserving linear shear with no shear band to a granular system composed of frictional photoelastic discs. The setup 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 shear-jammed 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 phi(SJ) approximate to 0.75, the smallest packing fraction supporting a shear-jammed state. We observe fragile states created under large shear strain over a range of phi phi(SJ). We also find a transition in the character of the quasistatic steady flow centered around phi(SJ) on the yield curve as a function of packing fraction. Near phi(SJ), the average contact number, fabric anisotropy, and nonrattler fraction all show a change of slope. Above phi(F) approximate to 0.7 the steady flow shows measurable deviations from the basal linear shear profile, and above phi(b) approximate to 0.78 the flow is localized in a shear band.