Amplitude-dependent rheological responses of axisymmetric grains

Abstract

Oscillatory shear flows of axisymmetric grains exhibit amplitude-dependent rheological responses, which is related to the evolution of the microstructure. In this work, it is shown that the highly ordered configuration of grains at steady-state shear flow undergoes microstructural rearrangement when subjected to shear oscillations. This rearrangement may lead to reduced ordering configurations which give rise to macroscale shear hardening, which can result in shear jamming if the applied shear traction is below the critical shear resistance. On the other hand, it was observed that applying oscillatory shear to the primary condensed shear flow enhances flowability due to microstructure rearrangement. In this study, we investigate the amplitude-dependent rheological responses of axisymmetric grains subjected oscillatory shear flows. First, we look into the evolution of grains alignment subjected to a range of oscillation amplitudes, where we show that the lower oscillation amplitudes have the potential to change the orientation from the ordered steady state to a completely disordered (isotropic) orientation. Next, we study the dependency of the shear flow resistance on the microstructure configuration, and show that the strain hardening and potential jamming have strong dependency on the oscillations amplitude. We also show that, in the case of jamming, the shear strain and the corresponding number of oscillation cycles depend not only on the grains aspect ratio but also on the oscillation amplitude.