Penetration in bimodal, polydisperse granular material.
N Kouraytem1, S T Thoroddsen1, J O Marston2
1Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia.
Physical Review. E
|December 15, 2016
Summary
Investigating sphere impacts into bimodal granular materials reveals a lubricating effect. Small grains reduce friction between larger particles when present in sufficient quantities, impacting penetration depth.
Area of Science:
- Physics
- Materials Science
- Granular Mechanics
Background:
- Granular materials exhibit complex behaviors under impact.
- Previous studies focused on monodisperse (single-sized) granular media.
Purpose of the Study:
- To investigate sphere impact penetration in bimodal granular media.
- To understand the effect of particle size composition and impact speed on penetration depth.
- To analyze the lubricating effect observed in mixed granular systems.
Main Methods:
- Experimental impact tests using spheres into granular beds of varying compositions.
- Analysis of penetration depth as a function of impact parameters and granular mixture properties.
- Correlation of data using packing fraction and critical packing fraction concepts.
Main Results:
- Penetration depths ranged from 0.5D₀ to 7D₀.
- Bimodal data required critical packing fractions for collapse, unlike monomodal data.
- A significant lubricating effect was observed with fine grains (∼30 μm) added to larger particles (∼200-500 μm) at >25% mass fraction and size ratio >3.
- This lubrication was most pronounced with rough-surfaced large particles.
Conclusions:
- The lubricating effect in bimodal granular media is attributed to small particles reducing intergrain friction between larger particles.
- Sufficient mass fraction of small grains is necessary to prevent them from merely rattling in voids.
- Understanding these effects is crucial for predicting impact dynamics in complex granular systems.
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