Solid-Fluid Transition under shear

H. Caps, F. Vivanco, F. Melo

The understanding of the solid fluid transition arising from an imposed shear on a granular material has remained elusive for decades.  We believe this is due in part to the lack of well defined experimental configurations, since previous works focused the problem in confined geometry only, i.e, constant volume.  To partially overcome this difficulty, we have designed a unique set-up which allows us to measure simultaneously, shear forces, shear rates and, more important global “dilatancy” (small density changes).   In addition, by developing a particle imaging velocimetry (PIV) technique, in conjunction with a novel photoelastic technique, we are able to follow particles trajectories and to measure the local force at every single particle. 

Figure 1. The upper panel sequence showing the distribution of force inside the granulate during a full cycle of shear. The lower panel shows the typical curves for shear force and dilatancy in a cycle.