(Dis)continuous shear thickening in frictionless granular media?

Continuous and discontinuous shear thickening are commonly observed in sheared dense suspensions but are still not fully understood. Although micro-friction at particle-particle contacts is widely accepted as the dominating origin of discontinuous shear thickening, if there is no interstitial fluid. With the help of discrete element simulations, we re-visit shear thinning/thickening of dry granular packings and their possible origins at the (micro) contact- and (meso) structure-scales. The focus is here on the steady-state shear resistance of non-cohesive frictionless polydisperse sphere packings from volume fractions below random loose packing, up to higher volume fractions, above random close packing. This intermediate (transitional) regime is challenging due to its densities above the range where standard kinetic theory works, well below the statically jammed systems, only partly touching the range of dense rheology. In the frictionless packings studied here, mostly continuous shear thickening behaviour is observed, with apparent discontinuous shear thickening due to inhomogeneous shear strain.