Abstract
In a recent paper [Phys. Rev. X 12, 031021], we reported experimental
observations of "ultrastable" states in a shear-jammed granular system
subjected to small-amplitude cyclic shear. In such states, all the particle
positions and contact forces are reproduced after each shear cycle so that a
strobed image of the stresses and particle positions appears static. In the
present work, we report further analyses of data from those experiments. We
examine the evolution of contact forces within a cycle after an ultrastable
state is formed, not just the strobed dynamics. We find that there are two
types of contacts: non-persistent contacts that reversibly open and close; and
persistent contacts that never open. We show that the non-persistent contacts
contribute a non-negligible amount to the emergent shear modulus. We also
analyze the spatial correlations of the stress tensor and compare them to the
predictions of a recent theory of the emergent elasticity of granular solids
(VCTG) [Phys. Rev. Lett. 125, 118002, arXiv:2204.11811]. We show that our
experimental results can be fit well by VCTG, assuming the uniaxial symmetry of
the contact networks. The fits reveal that the response of the ultrastable
states to additional applied stress is substantially more isotropic than that
of the original shear-jammed states. Our results provide important insight into
the mechanical properties of frictional granular solids created by shear.