Prolate Granular Materials

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Prolate Granular Materials

• Connected Networks, Jammed States, and Force
  Fluctuations

By Kenneth Desmond Advisor Dr. Scott Franklin
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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)

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A Jammed State

• 3 rods with an aspect ratio of 48
• An example of a jammed state without the aid of
  supportive walls

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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

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How Hard Must You Pull?
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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

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Solid-body Motion

• Force fluctuations are due to stick-slip motion
  on the surface of the walls

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Transition Region

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

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Pile Phase Space

• Transition from stick-slip to solid-body motion
  is gradual not sudden

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Pile Phase Space

• Well focus on the closed box since it spans all
  the different phases

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FFT Spectrum

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

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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