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

2. . 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

3. 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A. Fall and D. Bonn (unpublished)

4. No friction, applied shear stress
Experiments
2D foam

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

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

7. 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

8. Nature 2001
Science 2003

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

10. Frictional particles
Support simple scenario of dilation ?

11. 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