Contact Force Effects on Rheology of Dense Suspensions

The extreme rate dependence of dense suspensions has been related to the influence of contact forces, with tribological effects such as frictional interactions and other constraints on motion now generally accepted as playing some role. Theory and simulation have shown how contact with a frictional interaction, caused by overcoming a repulsive interparticle force, can lead to discontinuous shear thickening or shear jamming at large stress. Experimental study has shown that elements of this description are appropriate, but it is generally oversimplified. The influence of contact forces at small stress is found in the yielding behavior, and this is also considered here, for cases where an attractive interparticle force is involved. Measurement of particle frictional interactions is also discussed.