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Reverse Janssen effect with non-spherical grains
Adria Meca-Montserrat1,2, Iker Zamorano1, Caleb Anderson1
1University of Barcelona, Department of Condensed Matter Physics, Marti i Franquès 1, 08028 Barcelona, Spain.
The Janssen effect describes how granular materials in containers reach a constant apparent weight. This study finds that non-spherical grains cause this effect to diminish faster with increasing container diameter compared to spherical grains.
Area of Science:
- Physics
- Materials Science
- Fluid Mechanics
Background:
- Granular matter displays unique mechanical behaviors, deviating from typical fluid or solid responses.
- The Janssen effect explains weight saturation in granular columns due to wall friction, where added mass doesn't linearly increase bottom weight.
- A reverse Janssen effect, characterized by a weight overshoot, is observed in narrow cylinders with spherical grains.
Purpose of the Study:
- To experimentally investigate the influence of particle shape on the reverse Janssen effect.
- To determine how grain shape affects the transition from the reverse Janssen effect to the standard Janssen saturation.
- To analyze potential mechanisms explaining the observed impact of grain shape on granular material mechanics.
Main Methods:
- Experimental setup involving filling cylindrical containers with granular materials of varying shapes (spherical and non-spherical).
- Systematic variation of cylinder diameter and particle shape to observe changes in measured weight.
- Quantitative analysis of the apparent weight as a function of added mass and container dimensions.
Main Results:
- The reverse Janssen effect diminishes more rapidly with increasing cylinder diameter for non-spherical grains compared to spherical grains.
- Particle shape significantly influences the conditions under which the reverse Janssen effect is observed.
- Observed phenomena provide insights into the interplay between particle morphology, friction, and confinement in granular systems.
Conclusions:
- Particle shape is a critical factor modulating the mechanical response of granular materials.
- The transition dynamics of the Janssen effect are demonstrably altered by grain non-sphericity.
- Further research is warranted to fully elucidate the complex relationship between grain geometry and macroscopic granular behavior.
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