Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

The Jekyll and Hyde of granular materials uncovered

01.04.2004


Granular materials – which include everything from coal to coco pops – are physical substances that don’t quite fit into any of the known phases of matter: solid, liquid, or gas.



Keep the grains under pressure, vacuum-packed coffee for example, and you have solid-like behaviour; open the pack and pour it into a container and suddenly the grains flow freely like a liquid.

The changing personalities of granular materials can have devastating implications, for example the disturbance of the earth following an earthquake can be enough to trigger solid ground to turn to mush with catastrophic consequences.


Dr. Antoinette Tordesillas, a senior lecturer at the Department of Mathematics and Statistics at the University of Melbourne says, "Even a fractional advance in our understanding of how granular media behave can have a profound impact on the economic and general well-being of nations worldwide."

Yet, despite being second only to water on the scale of priorities of human activities, and believed to account for ten per cent of all energy consumed on Earth, the physics behind granular materials remain largely unknown.

Dr. Tordesillas says, "The reason for this is that these seemingly simple materials exhibit a rich and complex rheology."

Scientists have generally turned to the continuum theory for predicting the behaviours of solids and liquids – it looks at an object as a whole rather than the sum of its parts.

However, the theory collapses when applied to granular materials because information about the properties of the material at the particle level is missing – it treats a bag of sand as a solid block and does not contain information about the individual grains and how easily they rub and roll against each other.

An alternative is to model every single grain, which is what the discrete element method (DEM) does, but this technique is computationally intensive and extremely costly, and a handful of sand is about as much as current supercomputers can handle.

A more recent model, the enriched continuum model, is a hybrid of the continuum and DEM.

It uses the basic form of the continuum model but enriches it with information at the microstructural level, so the equation that describes a bag of sand is penetrated with information about the individual grains and how they interact with each other.

Dr. Tordesillas says, "The result is a picture that has a much higher resolution than that offered by continuum theory."

"At the correct level of resolution it is possible to see critical microstructures, called ’shear-bands’, which give insight into the failure properties and personality shifts of such materials."

"In a sense, we are endeavouring to understand what triggers the personality change in granular materials and the shear band is the key or signature microstructure that these materials manifest as they undergo a transition from solid to liquid."

Nobody has successfully managed to understand the nature of shear bands to date.

Now, the Mechanics and Granular Media Group of the Department of Mathematics and Statistics at the University of Melbourne, led by Dr. Tordesillas, have pioneered the first enriched continuum model capable of seeing shear bands.

Dr. Tordesillas says, "We have found a way to capture and predict not only the split personality but also the key transition mechanism."

"This entirely new level of predictive capability is unmatched by any other continuum model developed to date, and the beauty of it is that not only is it more computationally efficient than DEM, but all the underlying physics at the microscale level are there, fully exposed in the equations."

"By implementing this new breed of material model in computer simulations of granular processes, we hope to gain more accurate predictions and therefore better control of granular behaviour in real world situations."

The findings are published in the journals Powder Technology, Geotechnique, Acta Mechanica, Granular Matter, International Journal for Analytical and Numerical Methods in Geomechanics, BIT Numerik Mathematik, and the International Journal of Solids and Structures.

Elaine Mulcahy | EurekAlert!
Further information:
http://www.unimelb.edu.au/

More articles from Materials Sciences:

nachricht Research finds new molecular structures in boron-based nanoclusters
13.07.2018 | Brown University

nachricht 3D-Printing: Support structures to prevent vibrations in post-processing of thin-walled parts
12.07.2018 | Fraunhofer-Institut für Produktionstechnologie IPT

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: First evidence on the source of extragalactic particles

For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.

To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...

Im Focus: Magnetic vortices: Two independent magnetic skyrmion phases discovered in a single material

For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.

Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...

Im Focus: Breaking the bond: To take part or not?

Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.

A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...

Im Focus: New 2D Spectroscopy Methods

Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.

"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....

Im Focus: Chemical reactions in the light of ultrashort X-ray pulses from free-electron lasers

Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.

Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Leading experts in Diabetes, Metabolism and Biomedical Engineering discuss Precision Medicine

13.07.2018 | Event News

Conference on Laser Polishing – LaP: Fine Tuning for Surfaces

12.07.2018 | Event News

11th European Wood-based Panel Symposium 2018: Meeting point for the wood-based materials industry

03.07.2018 | Event News

 
Latest News

Subaru Telescope helps pinpoint origin of ultra-high energy neutrino

16.07.2018 | Physics and Astronomy

Barium ruthenate: A high-yield, easy-to-handle perovskite catalyst for the oxidation of sulfides

16.07.2018 | Life Sciences

New research calculates capacity of North American forests to sequester carbon

16.07.2018 | Earth Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>