Transcript Prolate Granular Materials - Rochester Institute of Technology

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