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Earthquakes, sandslides and space exploration – the hidden forces of granular materials


Researchers have developed a new experimental approach that sheds new light on the complex behavious of granular matter.

Stephen Hall, lecturer in Solid Mechanics at Lund University, has led an international team of researchers in their search of explanations to complex behaviour of granular materials. Their results have now been published in Physical Review Letters, and their analysis of granular mechanics can eventually lead to better predictions of landslides and earthquakes, and facilitate in the field of pharmaceuticals and food processing.

Granular materials, such as sand, have the amazing ability to support load, as we walk along a beach, yet also to flow like a fluid, as in an hourglass.

Understanding this complex behaviour is fundamental to understanding a wide range of current challenges, including building foundation design, powder compression for pharmaceutical pills, silo flow in agriculture and industrial processing. It is even fundamental for understanding earthquakes and designing rovers for space exploration. For example, how will landers move on extra-terrestrial soils?

"Understanding the mechanics of such granular materials is challenging since little is known about how external loads are transmitted through these materials. Until now there has been no way to see inside to measure the forces between particles in 3D assemblies of grains," says Stephen Hall, Senior Lecturer at the Division of Solid Mechanics, Lund University.

Stephen Hall from the Division of Solid Mechanics at University of Lund – with collaborators from Lawrence Livermore National Laboratory, the European Synchrotron Radiation Facility and California Institute of Technology – have developed a new experimental approach that sheds new light on this complicated problem.

The team used synchrotron x-ray techniques (3D tomographic imaging and 3D x-ray diffraction) to measure the organisation and strains of each of the grains in a granular assembly as it was slowly compressed. Then, using mathematical analysis, it was possible to obtain a map of the contact forces between the particles.

This map showed the pathways by which the forces were passed from the top to the bottom of the sample, indicating clear arrangements that changed and, in fact, became more distributed, as the load was increased.

Their work was published in the August 19th issue of Physical Review Letters. The novel experimental analysis of granular mechanics has a wide area of interest – from landslides and earthquakes to pharmaceuticals and food processing.

"These new experiments are in themselves very interesting in terms of what they reveal about the complex systems of grains, but the key will be how these new insights allow us to build better mathematical models of granular materials. With such models it will be possible to better understand dangerous natural phenomena such as landslides. It will also be possible to improve industrial processes like pharmaceutical tablet processing and even better predict how we will land on the soils of other planets," says Stephen Hall.

Article in Physical Review Letters

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