title: Shear modulus and dilatancy softening in granular packings above jamming.
abstract: We investigate experimentally the mechanical response to shear of a monolayer of bidisperse frictional grains across the jamming transition. We inflate an intruder inside the packing and use photoelasticity and tracking techniques to measure the induced shear strain and stresses at the grain scale. We quantify experimentally the constitutive relations for strain amplitudes as low as 10(-3) and for a range of packing fractions within 2% variation around the jamming transition. At the transition strong nonlinear effects set in: both the shear modulus and the dilatancy shear soften at small strain until a critical strain is reached where effective linearity is recovered. The scaling of the critical strain and the associated critical stresses on the distance to jamming are extracted. We check that the constitutive laws, together with mechanical equilibrium, correctly predict to the observed stress and strain profiles. These profiles exhibit a spatial crossover between an effective linear regime close to the inflater and the truly nonlinear regime away from it. The crossover length diverges at the jamming transition.
authors.affiliation: SPHYNX/SPEC, CEA-Saclay, URA 2464 CNRS, 91191 Gif-sur-Yvette, France and Université Paris-Sud, CNRS, Lab FAST, Bat 502, Campus Université, Orsay F-91405, France and Huygens-Kamerlingh Onnes Lab, Universiteit Leiden, P.O. box 9504, 2300 RA Leiden, Netherlands.
authors.forename: C
authors.initials: C
authors.lastname: Coulais
authors.affiliation: SPHYNX/SPEC, CEA-Saclay, URA 2464 CNRS, 91191 Gif-sur-Yvette, France and Université Paris-Sud, CNRS, Lab FAST, Bat 502, Campus Université, Orsay F-91405, France.
authors.forename: A
authors.initials: A
authors.lastname: Seguin
authors.affiliation: EC2M, ESPCI-ParisTech, UMR Gulliver 7083 CNRS, 75005 Paris, France.
authors.forename: O
authors.initials: O
authors.lastname: Dauchot