| This talk focuses on the roles played by stress anistropy and by dimensionality in dense granular materials near jamming and subjected to continuous shear. We find for 2D systems that simple measures such as P(F) are sensitive to stress anisotropy. Moreover, the nature of the onset of jamming is strongly affected by anisotropy. In particular, an unjammed isotropic material that is subject to shear strain (e.g. via biaxial shear) can jam. When an isotropic jammed system at constant density is sheared, it typically undergoes relatively local failure events (force chains break, for example) and then returns to a new jammed state at reduced pressure and shear stress. In a space of density and shear stress (at zero effective temperature) there is a possibly fuzzy boundary which the system does not cross. For such systems, it is possible to sketch a jamming surface in pressure, shear stress and density. If a material is subject to steady shear strain (e.g. Couette shear in physical experiments, plain strain in models), the system presumably explores a range of states near such a boundary. The second part of this talk explores a set of both 2D and 3D experiments which involve Couette and approximations to plane shear. A feature that is common to both 2D and 3D is the formation of shear bands. An interesting question concerns the commonality across dimensionality of these bands, and possible insights about their properties and origins. |
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