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A new method for measuring grain displacements in granular materials by X-ray computed tomography

M.H. Khalili
Sébastien Brisard
Michel Bornert
Jean-Michel Pereira
Matthieu Vandamme
Jean-Noël Roux

Abstract

We aim to measure the individual grain displacements in a granular material under constant load (creep). X-ray computed tomography imaging provides images of the granular medium microstructure during the experiment, and discrete volumetric image correlation (DV-DIC) [1] allows the determination of the grain individual rigid body motion from the reconstructed tomography images. However, for short-term creep, and time-resolved experiments in general, the sample evolutions can be very quick and occur before the full tomography scan is complete. This constitutes a serious limitation of standard experimental procedures for the investigation of the micromechanics of the creep of granular media at the grain scale. We present a new method for measuring grain displacements, that overcomes the above-mentioned limitation. Indeed, in a granular material, assuming no breakage occurs, each grain undergoes a rigid body motion. Therefore, the displacement field reduces to a set of six degrees of freedom per grain. This suggests that the information contained in a full set of projections (necessary to perform an accurate 3D reconstruction) is excessively redundant for the determination of the grain displacements. Our method requires only few projections of the sample at its current state, thus reducing dramatically the acquisition time. Displacements are estimated from the projections directly, without 3D reconstruction. Our method is formulated as an inverse problem. A forward model based on Beer-Lambert's law is developed to efficiently perform numerical projections. The grain displacements are estimated by fitting the numerical projections to experimental projections of the current state of the sample. We also study the sensitivity of the estimated displacements to image noise, both numerically and through a theoretical model which highlights the influence of the setup parameters on the measurements. The method has been validated and its accuracy assessed against 2D and 3D numerical experiments on virtual microstructures.
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Dates and versions

hal-01194699 , version 1 (07-09-2015)

Licence

Attribution - NonCommercial - CC BY 4.0

Identifiers

  • HAL Id : hal-01194699 , version 1

Cite

M.H. Khalili, Sébastien Brisard, Michel Bornert, Jean-Michel Pereira, Matthieu Vandamme, et al.. A new method for measuring grain displacements in granular materials by X-ray computed tomography. 2nd International Conference on Tomography of Materials and Structures (ICTMS 2015), INRS-ETE, Jun 2015, Quebec city, Canada. ⟨hal-01194699⟩
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