Prolate Granular Materials

Connected Networks, Jammed States, and Force Fluctuations

By: Kenneth DesmondAdvisor: 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