Granular Flow Module - Gravity and Granular Materials (GGM)

Principal Investigator: Robert P. Behringer, Duke
Project Scientist: Allen Wilkinson, Glenn Research Center
Project Manager: John Caruso, Glenn Research Center

Currently scheduled to be launched: Flight #TBD - Date 02/2008

Why:
Handling granular materials is pervasive in our economy but mechanical behavior of granular materials is poorly understood. Unpredictability leads to clogged chutes and catastrophic failures of industrial silos, for example. Also when uniform mixing of medicinal components is critical, segregation still can occur.
The presence of gravity complicates the behavior such that models that capture the physics correctly are hard to verify. Only low-g 3-D systems can display the basic physics needed for correct models.

How:
The low-g apparatus is an annular cylinder with one moving end surface to shear a 3-D volume of 1 mm glass beads. The volume fractions of beads will range from gas-like to liquid-like regimes to probe the jamming transition. Granular clustering will be explored. Video sequences will quantify particle velocity statistics.
The annulus wall will be instrumented with 20 three-axis shear and normal stress sensors that will be able to record both the single particle bounces and the huge forces from a force chain spanning the cell. The time trace of these forces will be analyzed statistically. The volume fractions will be varied.

Top view of 2-D granular system for 1-g work. Photoelastic disks in a shearing annulus. Bright tangled lines are jamming force chains. They show the very irregular way forces arise.

Impact/Benefits:
Granular materials flow is routine in human activity from mining to blending pharmaceuticals, from grain handling to highway traffic jams, and even to Martian soil mechanics. Excessive downtime is required for humans to fix the unexpected. The economic impact is vast.
At the scientific level the statistical mechanics of granular materials is rich for the discovery of new physics, non-local and non-equilibrium.

Granular Flow Module - Gravity and Granular Materials (GFM-3)

Next Flight Experiment: CCF

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