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Stress Relaxation for Granular Materials near Jamming under Cyclic Compression
Somayeh Farhadi1, Alex Z Zhu1, Robert P Behringer1
1Department of Physics and Center for Nonlinear and Complex Systems, Box 90305, Duke University, Durham, North Carolina 27708, USA.
Physical Review Letters
|November 14, 2015
Summary
Granular materials transition between jammed and unjammed states under cyclic compression. Above a critical packing fraction, pressure stabilizes; below it, pressure slowly relaxes, with ellipses showing hindered collective motion.
Area of Science:
- Physics
- Materials Science
- Complex Systems
Background:
- Granular materials exhibit complex behaviors, including jamming and unjamming transitions.
- Understanding the mechanical properties of granular systems is crucial for various applications.
Purpose of the Study:
- To investigate isotropically jammed states in semi-2D granular materials under cyclic compression.
- To analyze the evolution of pressure and structure in jammed states of ellipses and disks.
Main Methods:
- Cyclic compression of semi-2D granular systems composed of identical ellipses or bidisperse disks.
- Monitoring the average pressure (P) and structural evolution across compression cycles.
- Analyzing the relaxation dynamics of pressure and collective particle motion.
Main Results:
- A transition point (ϕm) was identified, above which pressure (P) remains stable over cycles.
- Below ϕm, pressure (P) exhibits slow relaxation, with increasing timescales at higher packing fractions.
- Elliptical particles demonstrate hindered collective motion compared to disks due to rotational constraints.
Conclusions:
- Cyclic compression reveals distinct pressure behaviors in granular materials based on packing fraction.
- The relaxation dynamics are dependent on both pressure and particle shape.
- Rotational constraints significantly impact the collective dynamics of elliptical granular systems.
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