Granular Materials

Annular shear cell with leaf spring boundary
Annular shear cell with leaf spring boundary

The flow of dense granular materials at low inertial numbers cannot be fully characterized by local rheological models; several nonlocal rheologies have recently been developed to address these shortcomings. To test the efficacy of these models, we perform experiments in a quasi-2D annular shear cell with a fixed outer wall and a rotating inner wall, using photoelastic particles. The apparatus is designed to measure boundary stresses laser-cut leaf springs around the outer boundary. Current researchers: Zhu Tang

  • Zhu Tang, Theodore A. Brzinski, and Karen E. Daniels. “Granular rheology: measuring boundary forces with laser-cut leaf springs.” Powders & Grains 2017 EPJ Web of Conferences 140, 03035 (2017) [Link] [PDF]

High-speed movie of a rarefaction wave in a photoelastic granular material
High-speed movie of a rarefaction wave in a photoelastic granular material

Many of our granular experiments use photoelastic particles, allowing us to visualize internal stresses. In the picture at left, particles with many light-colored fringes are those carrying higher force. In some cases, we perform a semi-quantitative analysis to reveal the dynamics under loading or sound propagation. Where needed, we analyze each particles pattern of fringes to determine the vector forces present at each interparticle contact. The paper below provide a summary of how these methods work from both a practical standpoint (materials, lighting considerations), as well the underlying optics. Current researchers: Jonathan Kollmer

  • Karen E. Daniels, Jonathan E. Kollmer and James G. Puckett. “Photoelastic force measurements in granular materials.” Review of Scientific Instruments 88, 051808 (2017) [Link] [PDF]
  • Open Source Code by Jonathan Kollmer: PeGS