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PROGRESS ARTICLESlow relaxation and compaction of
granular systemsGranular materials are of substantial importance in many industrial and natural processes, yet their complex behaviours, ranging from mechanical properties of static packing to their dynamics, rheology and instabilities, are still poorly understood. Here we focus on the dynamics of compaction and its jamming phenomena, outlining recent statistical mechanics approaches to describe it and their deep correspondence with thermal systems such as glass formers. In fact, granular media are often presented as ideal systems for studying complex relaxation towards equilibrium. Granular compaction is defi ned as an increase of the bulk density of a granular medium submitted to mechanical perturbation. This phenomenon, relevant in many industrial processes and widely studied by the soil mechanics community, is simple enough to be fully investigated and yet reveals all the complex nature of granular dynamics, attracting considerable attention in a broad range of disciplines ranging from chemical to physical sciences.PATRICK RICHARD1*, MARIO NICODEMI2,
RENAUD DELANNAY1, PHILIPPE RIBIRE1
AND DANIEL BIDEAU11Groupe Matire Condense et Matriaux, UMR CNRS 6626,
Universit de Rennes I, 35042 Rennes Cedex, France2Universit di Napoli Federico II, Dipartimento di Scienze Fisi
che, INFN and INFM Coherentia, Via Cintia - 80126 Napoli, Italy
*e-mail: [email protected] materials are ubiquitous in nature and are the
second-most manipulated material in industry (the fi rst
one is water), encountered, for instance, in technological
applications ranging from pharmaceutical, food,
powders, mechanosynthesis and semiconductor
industries up to geological granular fl ows, such as
debris or pyroclastic fl ows and rock avalanches.
Granular media, such as powders or sand, are very
simple, made of discrete particles of size larger than
100 m often interacting with each other only through
dissipative contact forces. Without an external drive
their kinetic energy is rapidly lost and they are thus
referred to as non-thermal systems. Despite this
deceptive simplicity, granular matter exhibits many
complex behaviours, such as size segregation, formation
of arches, convection rolls, pattern formation and
dynamical instabilities16. Thus, although individual
grains are solid, it is inappropriate to classify their
collective properties as entirely solid-like or liquid-like.
Currently, no rheological laws exist for such materials
and their industrial manipulations are mainly based on
empirical observations.This progress article deals with a simple, yet
fundamental, phenomenon in the physics of granular
materials:...