The effect of rolling friction on the rheology and kinematics of shear-thickening dense suspensions
Sliding friction lowers the jamming packing fraction of dense suspensions and, when activated by stress, drives non-inertial shear thickening. Additional rolling resistance lowers the jamming packing fraction further and can represent effects of particle roughness or angularity. How it changes particle motion on the approach to jamming remains unclear. Using stress-controlled two-dimensional discrete-element simulations, we compare a sliding-only suspension with systems having either uniform or surface-varying rolling friction. At fixed packing fraction, adding rolling friction changes continuous shear thickening into discontinuous shear thickening. At the same distance from the stress-dependent jamming point, $Δϕ=ϕ-ϕ_m(σ)$, however, the flow curves nearly collapse, showing that the rheological effect arises largely from the shift in $ϕ_m$. Guided by this collapse, we compare particle kinematics in the high-stress thickened state at matched $Δϕ$, revealing differences hidden by the similar bulk response. Translational velocity correlations extend over several particle diameters, whereas rotational correlations remain local. Rolling friction promotes co-rotation at contact in place of strong counter-rotation and suppresses rotational relative to translational fluctuations. Rotation nevertheless becomes increasingly important near jamming in every case. The suspension with surface-varying rolling friction follows the behavior of a uniform system with $μ_r\approx0.3$ because the coefficients sampled at contacts lie well below the surface average value, here $μ_r\approx0.5$. Thus, $Δϕ$ largely organizes the shear-thickening rheology, but not the particle kinematics. These retain a distinct signature of the rolling constraint that must be considered when rolling friction is used to model rough or angular particles.