University of Amsterdam The Role of Friction and Shear stress in the Jamming Transition Antonio Coniglio Discussion Peter Schall University of Amsterdam

. No friction, applied shear stress h G l s h = / v Viscosity Newtonian behavior ? . s = h g System still homogeneous ? Shear banding ? Protocol l z s h = / v shear

No friction, applied shear stress Experiments Grains density-matched (no sedimentation) f>0.62 stress f<0.62 strain A. Fall and D. Bonn (unpublished)

No friction, applied shear stress Experiments 2D foam

How reliable is fc ? No friction, applied shear stress Hysteresis z x 16 d y F 16 x 16 x 8 = 2048 particles How reliable is fc ? O‘Hern et al. 2003

Is fc a good measure ? No friction, applied shear stress Hysteresis z x 16 d y F 16 x 16 x 8 = 2048 particles Is fc a good measure ? Confining pressure p Particle overlap d d

Model: motion in energy landscape W(x) No friction, applied shear stress Model: motion in energy landscape W(x) Crystal potential Jamming : general for solids, crystalline and amorphous systems

Nature 2001 Science 2003

Frictional particles Simulations at V = const but particles want to dilate ... Behavior at p = const ?

Frictional particles Support simple scenario of dilation ?

Frictional particles Experimental examples ? Relation with “Shear thickening“ ? (Suspensions under rapid shear, e.g. cornstarch, bullet-proof wests) Constant volume or pressure ? Constant pressure: Laplace pressure that holds particles in suspension