Strain dependent vorticity in sheared granular media

¹ Department of Mechanical Engineering & Materials Science, Yale University, New Haven, Connecticut 06520, USA
² Physical Chemistry and Soft Matter, Wageningen University & Research, Stippeneng 4, 6708 WE Wageningen, the Netherlands
³ Laboratoire de Mécanique et Génie Civil, Université de Montpellier, CNRS, Montpellier, France
⁴ Department of Geotechnical Engineering, College of Civil Engineering, Tongji University, Shanghai, 200092, China

^* e-mail: zhenghu@tongji.edu.cn

Published online: 7 June 2021

Abstract

Displacement fields in sheared particle packings often display vortex-like structures that reveal essential features about the mechanical state of the collection of particles. There are several metrics to quantify these flow field features, yet extracting such quantitative metrics from flow field or particle tracking data involves making numerous choices on the time and length scales over which to average. Here we employ a much used experimental data set on sheared disk packings to explore how such arbitrary data mining choices affect the obtained results. We focus on calculating the strain dependent vorticity, as this metric is a differential method hence potentially sensitive to the way it is computed. We find that the total surface area with an absolute vorticity above a certain threshold approaches a plateau value as shear progresses. This plateau value exhibits a non-monotonic dependence on packing fraction. We also show which range of choices yields results that can support an analysis method independent, physical interpretation of the flow field data.