A publication in Scientific Reports

Smart void filling



Researchers from GRASP (CESAM Research Unit/Faculty of Sciences) are highlighting new grain flow properties that allow optimal compositions to be obtained for densifying mixtures. This study, which is an important step in understanding binary granular mixtures and their compaction, has many applications, particularly in the pharmaceutical and construction industries. The results were published in Scientific Reports (1).

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veryone has already seen this video in which a teacher completely fills a jar with marbles and then adds a large amount of sand that fills - almost - the gaps left between the marbles, demonstrating that there is a significant empty space between these marbles. The principle of inserting small grains between larger ones is used in many areas to increase the density of materials. This is particularly the case for building materials or pharmaceutical powders to optimize, for example, key parameters in the filling of drug matrices, facilitate their compaction, etc. The fundamental question then arises : what should be the optimal composition (the amount of small and large particles) for each grain mixture.


Melanges grains

Pictures and numerical simulations of two extreme cases encountered with binary mixtures and for three different size ratios. The colored circles are guides to detect the large beads in the mixture. (top row) When the fraction f of small particles is low, they fill the voids between large beads. When the size ratio α is large enough, they may percolate into this voids. The packing of large beads is broken and restructured by small ones. (bottom row) When f is large, small particles dominate the packing since large beads can be seen as solid bodies entirely surrounded by small particles.


While the previous studies were reserved for numerical simulations, the studies conducted by the researchers of the GRASP Lab - Group of Research and Applications in Statistical Physics - were able to physically test their theory by using the instruments of GranuTools, an University of Liège spin-off. Thanks to the advanced tools developed by the spin-off, the researchers were able to study granular mixtures of grains of different sizes and carry out a systematic study that reveals the complex physics of these systems. In addition to obtaining optimal compositions for densifying mixtures, the researchers studied their flow properties and were able to identify different physical properties depending on whether or not the smallest grains percolate into the voids left by the larger ones. This is an important step that has just been taken by ULiège researchers from an experimental point of view. The results of this research can be directly integrated by manufacturers in order to optimize both the flow and density of their powders, in all possible applications from food processing to additive manufacturing.

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Optimal packing of granular mixtures

Researchers from GRASP - Group of Research and Applications in Statistical Physics - are discovering new grain flow properties that provide optimal compositions for densifying mixtures.

This research was published in open access in Scientific Reports. https://www.nature.com/articles/s41598-019-43519-6

Scientific reference

(1) Pillitteri S., Lumay G., Opsomer E. & Vandewalle N., From jamming to fast compaction dynamics in granular binary mixtures, Scientific reports 9, 13 May 2019. The publication is in open access

Contacts

GRASP CESAM Research Unit - Faculty of Sciences

Salvatore PILLITTERI

Nicolas VANDEWALLE

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