Rheology of weakly wetted granular materials: a comparison of experimental and numerical data

Abstract

Shear cell simulations and experiments of weakly wetted particles (a few volume percent liquid binders) are compared, with the goal to understand their flow rheology. Application examples are cores for metal casting by core shooting made of sand and liquid binding materials.The experiments are carried out with a Couettelike rotating viscometer. The weakly wetted granular materials are made of quartz sand and small amounts of Newtonian liquids. For comparison, experiments on dry sand are also performed with a modified configuration of the viscometer. The numerical model involves spherical, monodisperse particles with contact forces and a simple liquid bridge model for individual capillary bridges between two particles. Different liquid content and properties lead to different flow rheology when measuring the shear stress-strain relations. In the experiments of the weakly wetted granular material, the apparent shear viscosity η g scales inversely proportional to the inertial number I, for all shear rates. On the contrary, in the dry case, an intermediate scaling regime inversely quadratic in I is observed for moderate shear rates. In the simulations, both scaling regimes are found for dry and wet granular material as well.

Micro–macro transition and simplified contact models for wet granular materials

“…Earlier studies on wet granular materials have shown that the presence of liquid bridges between the particles results in an increasing steady-state cohesion of the materials [12,13,15,27]. Our earlier studies show that the steady-state cohesion c * increases non-linearly with increasing liquid bridge volume.…”

“…This model equation is applicable for mono-disperse particles [12,19], which has been actually extended to poly-disperse system of particles Ref. [14].…”

“…In earlier studies [12,27,40,41], the shear band region was identified by the criterion of large strain rate, e.g., higher than a critical strain rate of 0.08 s −1 . In this paper, the shear band center region is defined by strain rates higher 80 % of the maximum for different heights in the shear cell.…”

“…The tensile forces generated at particle level result in cohesion at macroscopic scale. Earlier studies have been done for liquid bridge in the pendular regime to understand the effect of liquid bridge volume and contact angle on different macroscopic quantities like the steady-state cohesion, torque, and shear band properties [12][13][14][15][16]. Other studies for unsaturated granular media observe fluid depletion in shear bands [17,18].…”

Effect of cohesion on shear banding in quasistatic granular materials

“…So far, only a few attempts have been made to answer this question, concerning dense metallic glasses [27,28], adhesive emulsions [29,30], attractive colloids [31][32][33], cemented granular media [34], wet granular media [35,36] and clayey soils [37]. Recently, rheological studies on adhesive emulsions and colloids [29][30][31]33] reported that the presence of attractive forces at contact affects shear banding by affecting flow heterogeneity and wall slip.…”