Prolate Granular Materials Connected Networks, Jammed States, and Force Fluctuations By: Kenneth Desmond Advisor: Dr. Scott Franklin

What We are Studying We study long thin rods and their ability to jam. We Characterize these rods by their aspect ratio, the ratio between the rod length and the rod diameter (L/d)

A Jammed State 3” rods with an aspect ratio of 48 An example of a jammed state without the aid of supportive walls

Setup Aspect Ratio (L/d) ranges from 8 to 48 with the diameter of the rods (d) being 1/16” or 1/8” The tube diameter ranges from 1.25” to 4” with a ball diameter of ¼” As the ball moves throw a granular medium the force sensor relays the information to the computer as voltage data The voltage is then converted into a force readout, based on earlier calibration

How Hard Must You Pull?

Stick-slip Motion Linearly increasing force when ball is at rest followed by a very short burst of motion Fluctuations are due to granular rearrangement

Solid-body Motion Force fluctuations are due to stick-slip motion on the surface of the walls

Transition Region Transition region marked by small moments of solid-body like motion followed by particle rearrangements that bring the ball to stop

Pile Phase Space Transition from stick-slip to solid-body motion is gradual not sudden

Pile Phase Space We’ll focus on the closed box since it spans all the different phases

FFT Spectrum Ordinary granular materials scale as f -2 (Albert et al.) Dry friction scales as f -1

Conclusion This system can exhibit three different phases These phases depend mostly on aspect ratio and normalized tube diameter Also the pile can form force chains that result in forces must greater then the pile weight with jam states being very strong and rigid