Characterization of shear zones in soft granular beds by means of a novel magnetic resonance imaging technique

Abstract

We introduce a new Magnetic Resonance Imaging technique to study the geometry of shear zones of soft, low-frictional and hard, frictional granular materials and their mixtures. Hydrogel spheres serve as the soft, low-frictional material component, while mustard seeds represent rigid, frictional grains. Some of the hydrogel spheres are doped with $$\hbox {CuSO}_4$$ CuSO 4 salt to serve as tracers. A cylindrical split-bottom cell is sheared stepwise and the shear profiles are determined from the differences of tomograms after successive shear steps, using Particle Imaging Velocimetry and Particle Tracking Velocimetry. We find that the shear zone geometry differs considerably between soft grains submersed in water and the same material without the embedding fluid. Graphic abstract

Shear zones in granular mixtures of hard and soft particles with high and low friction

“…Following the findings of this study and the qualitative agreement of our results with the observations noted by Wang et al, 11 it becomes evident that mixtures of soft, slippery and hard frictional grains demonstrate shear bands of variable width for increasing mixing ratio, which evolves nonmonotonically with increasing values of the ratio. Since the materials of interest have two independent material parameters differing distinctly, namely friction and elastic modulus, it is interesting to look into their individual effects on the shear band characteristics.…”

“…With a further increase of X , the shear band narrows and moves outwards in the shear cell. The non-monotonic trend of the width of the shear band with increasing X was also observed by Wang et al 11…”

“…The inner radius of the shear cell is R 0 = 75 mm. This numerical setup is similar to that employed in the experimental work by Wang et al , 11 with the difference that the experimental configuration incorporates an additional small rod in the center of the cell, where the shear load was imposed.…”

“…Wang et al 11 observed experimentally a notable difference in the shear band properties between samples made of pure materials and mixtures. It was observed that the shear zones of the mixtures are wider than those of the pure materials.…”

“…The findings of Wang et al 11 established that mixtures of hard and soft particles exhibit wider shear zones than assemblies made of only one of the individual materials (only hard or only soft particles). However, the underlying reason for this behavior remains unclear.…”