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Cam EFLS A. J. Kabla


Granular matter

Local stress measurements in a 3D grain pile

Our understanding of the elasticity and rheology of disordered materials, such as granular piles, foams, emulsions or dense suspensions relies on improving experimental tools to characterize their behaviour at the particle scale. While 2D observations are now routinely carried out in laboratories, 3D measurements remain a challenge. In this paper, we use a simple model system, a packing of soft elastic spheres, to illustrate the capability of X-ray microtomography to characterise the internal structure and local behaviour of granular systems. Image analysis techniques can resolve grain positions, shapes and contact areas; this is used to investigate the material's microstructure and its evolution upon strain. In addition to morphological measurements, we develop a technique to quantify contact forces and estimate the internal stress tensor. As will be illustrated in this paper, this opens the door to a broad array of static and dynamical measurements in 3D disordered systems.

Mapping forces in a 3D elastic assembly of grains
Mohammad Saadatfar, Adrian P. Sheppard, Tim J. Senden, Alexandre J. Kabla
Journal of the Mechanics and Physics of Solids 60:55-66 (2012)

Quasistatic flows and Reynolds dilatancy

The quasi-static rheology of granular matter is a stubborn problem. In this regime, the structure of the pack controls the mechanical response but also depends on the whole plastic history, leading to singular behaviours such as flow localization or memory effects. The coupling between structure and flow is often associated with the Reynolds dilatancy principle, which states that the density of a random pack decreases with increasing strain. In order to obtain a quantitative description of grain packing dilatancy, we use real time X-Ray digital imaging, associated with a specific image processing algorithm. Our technique allows local and time resolved measures of grain displacement fields and density variations. We observe clear correlations between the shear history and the local density, leading to a phenomenological relationship between them.
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Dilatancy in slow granular flows
A. Kabla and T. Senden
Phys. Rev. Lett. 102:228301 (2009).

Pre-avalanche dynamics

X-ray observation of micro-failures in granular piles approaching an avalanche
A. Kabla, G. Debregeas, J.-M. di Meglio and T. Senden
EuroPhysics Letter 71:932 (2005).


Contact dynamics under vibration

Contacts Dynamics of a Gently Vibrated Granular Pile
A. Kabla and G. Debregeas
Phys.Rev.Lett. 92:035501 (2004).


Structural analysis of granular packs

The geometry and the number of contacts of monodisperse sphere packs using X-ray tomography
M. Saadarfar, A. Kabla, T.J. Senden and T. Aste
Powders and Grains 2005 R. Garcia-Rojo, H.J. Hermann and S. McNamara, Eds., Volume I, 2005, A.A. Balkema Publishers, London, ISBN 0 415 38348 X, pp. 33-36.