Granular Materials
Dating back to 1300 B.C., the word ‘sand’ (沙) had already been used in Chinese bronze inscriptions as one of the earliest words. The desire to communicate on sand at the very beginning of the language evolution demonstrates the ubiquity of granular matter, i.e., large agglomerations of macroscopic particles. Since then, the attempts of mankind to describe and understand such a material have never stopped. For example, in the epic poem ‘On the nature of things’ written in around 55 B.C., Lucretius describes granular flow as the following:
Is quite as easy as drinking water down,
And they, once struck, roll like unto the same.”
Physics behind a sandbox
Adding a little bit of water into sand enhances the stability of the latter dramatically, giving rise to the fascinating world of sand art.
This is an example where a change of ‘microsopic’ particle-particle interactions (cohesive force in this case) determines ‘macrosopic’ (mechanical stability in this case) properties of a material.
Is it really deterministic?
Sand grains: What we know and don’t know about them?
‘To see a world from a grain of sand, and a heavon from a wild flower …’
The poem Auguries of Innocence by William Blake illustrates one of the complexities of granular physics: Each grain of sand is unique and the entirety of particle-particle interactions in a sand pile is unpredictable. How to bridge the ‘microscopic’ and ‘macroscopic’ worlds of sandgrains is the key question we are trying to address.
While walking on a beach, one intermittently experiences the transition of wet sand between a rigid, solid-like state and a fluid-like state, leaving behind the stress loading history in the form of footprints (see the above title page). However, behaving like does NOT mean that we can simply treat them as normal states of matter because interactions between sand grains (e.g., a grain falling on the ground won’t jump back to its original height) cost energy. As a matter of fact, over 10 percent of world energy production is used to process granular materials (e.g., sand) because of the ubiquity of granular materials in nature, industrial sectors and our daily lives.
As such, a better understanding, predicting, and controlling the collective behavior of granular materials is a field of building fundamentals for a wide range of applications with substantial impact on our society: From the prediction of natural disasters (e.g. desertification, earthquake, landslide, debris flow), through the enhancement of energy efficiency in industries (e.g. process engineering, geo-technique, pharmaceutics, additive manufacturing), to space exploration (e.g. landing, exploring and constructing on celestrial objects).
How to? The objective is to bridge the `micro-‘ (particle) and `macroscopic’ (collective) scales of granular materials, and to extend the bridge to a broader perspective and a cross-disciplinary direction.
..more introduction? See my habilitation thesis
Consequently, ongoing research can be categorized into the following parts: From single particle bouncing to collective motion.
Impact
Wet impact model
Granular drag
Assembly
Clustering and melting in 2D
Drop-on-demand
Information on previous projects can be found HERE.
