Signatures of shear thinning-thickening transition in steady shear flows of dense non-Brownian yield stress systems

Steady shear flows of dense athermal systems composed of soft disks are investigated via non-equilibrium molecular dynamics simulations, from which we sort out links among the structure, dynamics, and shear rheology. The systems at rest are jammed packings of frictionless disks with a nonzero yield stress. Driven by low shear rates, the flows shear thin due to the presence of the nonzero yield stress, but transit to shear thickening above a crossover shear ratec γc. At γc, we observe the strongest structural anisotropy in the pair distribution function, which serves as the structural signature of the shear thinning-thickening transition. We also observe dynamical signatures associated with the transition: Atγc, scaling behaviors of both the mean squared displacement and relaxation time undergo apparent changes. By performing a simple energy analysis, we reveal an underlying condition for the shear thickening to occur: d(lnTg)/ d(lnγ)>2g with Tg the kinetic temperature. This condition is confirmed by simulations.