Experimental micro-mechanics of granular media studied by x-ray tomography: recent results and challenges

Andò, Edward; Viggiani, Gioacchino; Hall, Stephen A.; Desrues, Jacques

doi:10.1680/geolett.13.00036

Cited by 126 publications

(75 citation statements)

References 8 publications

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“…Experimentally, setup allowing a full-field observation of the strain repartition during the loading are scarce [4,7,8] and there has been a long debate if shear bands emerge before, at or after the peak of the loading curve. Recent progresses in the detection methods [9,10] have allowed to observe intermittent inhomogeneities in the strain field occuring before failure [11][12][13]. Those results have renewed (a) axelle.amon@univ-rennes1.fr the interest for this field of research with a particular interest for the understanding the microscale processes at the origin of the shear bands formation [14].…”

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confidence: 99%

Experimental study of shear band formation: Bifurcation and localization

Nguyen¹,

Amon²

2016

EPL

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-We report the experimental observation of the bifurcation at the origin of localization of the deformation in a granular material submitted to uniaxial compression. We present a quantitative characterization of the heterogeneity in the strain field repartition allowing to evidence objectively the existence of a bifurcation initiating the shear bands formation process. We show that this bifurcation is supercritical and has no clear signature on the stress-strain curve. At the bifurcation, a symetry breaking occurs characterized by the emergence of a well-defined orientation corresponding to the Mohr-Coulomb angle. Yet, plasticity is still diffuse and the shear band extension is of the order of the sample width. While loading proceeds, the shear band narrows until it reaches, after the peak of the stress-strain curve, a stationary width.

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confidence: 99%

Experimental study of shear band formation: Bifurcation and localization

Nguyen¹,

Amon²

2016

EPL

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“…7,8 It may be in turn to march on to the verification in 3D by numerical simulation, while 3D diffuse modes inside granular materials are difficult to observe experimentally, even by the most updated 3D CT measurement. 9 In this paper, with the aim of verifying that hypothesis, the mechanism of the formation of experimentally observed shear band patterns in Figure 1A,B is elucidated with the aid of numerical studies of diffuse bifurcations and 3D shear band patterns of granular materials. Shear bands on a cubic granular materials are simulated by numerical bifurcation analysis using nonlinear finite-element analysis for finite strains and the subloading surface Cam-clay plasticity model.…”

Section: Introductionmentioning

confidence: 84%

Diffuse bifurcations engraving diverse shear bands in granular materials

Yamakawa

Ikeda

Saiki

et al. 2017

Num Anal Meth Geomechanics

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SummaryShear bands with characteristic spatial patterns observed in an experiment for a cubic or parallelepiped specimen of dry dense sand were simulated by numerical bifurcation analysis using the Cam-clay plasticity model. By incorporating the subloading surface concept into the plasticity model, the model became capable of reproducing hardening/softening and contractive/dilative behavior observed in the experiment. The model was reformulated to be compatible with the multiplicative hyperelasto-plasticity for finite strains. This enhanced constitutive model was implemented into a finite-element code reinforced by a stress updating algorithm based on the return-mapping scheme, and by an efficient numerical procedure to compute critical eigenvectors of elastoplastic tangent stiffness matrix at bifurcation points. The emergence of diamond-and column-like diffuse bifurcation modes breaking uniformity of the materials, followed by the evolution of shear bands through strain localization, was observed in the analysis. In the bifurcation analysis of plane strain compression test, unexpected bifurcation modes, which broke out-of-plane uniformity and led to 3-dimensional diamond-like patterns, were detected. Diffuse bifurcations, which were difficult to observe by experiments, have thus been found as a catalyst creating diverse shear band patterns.

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“…The angularity of the grains and the grading of the sand created important challenges during image processing, especially regarding the segmentation of the particles and the definition of a size descriptor to obtain the mean diameter of the particles. Andò et al (2013) describe the challenges to overcome, regarding granular mechanics and image processing.…”

Section: Introductionmentioning

confidence: 99%

Evolution of deformation and breakage in sand studied using X-ray tomography

et al. 2018

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Particle breakage of a granular material can cause significant changes in its microstructure, which will govern its macroscopic behaviour; this explains why the mechanisms leading to particle breakage have been a common subject within several fields, including geomechanics. In this paper, X-ray computed micro-tomography is used, to obtain three-dimensional images of entire specimens of sand, during high-confinement triaxial compression tests. The acquired images are processed and measurements are made on breakage, local variations of porosity, volumetric strain, maximum shear strain and grading. The evolution and spatial distribution of quantified breakage and the resulting particle size distribution for the whole specimen and for specific areas are presented here for the first time and are further related to the localised shear and volumetric strains. Before peak stress is reached, compaction is the governing mechanism leading to breakage; neither compressive strains nor breakage are significantly localised and the total amount of breakage is rather low. Post peak, in areas where strains localise and breakage is present, a dilative volumetric behaviour is observed locally, as opposed to the overall compaction of the specimen. Some specimens exhibited a compaction around the shear band at the end of the test, but there was no additional breakage at that point. From the grading analysis, it is found that mainly the grains with diameter close to the mean diameter of the specimen are the ones that break, whereas the biggest grains that are present in the specimen remain intact.

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Experimental micro-mechanics of granular media studied by x-ray tomography: recent results and challenges

Cited by 126 publications

References 8 publications

Experimental study of shear band formation: Bifurcation and localization

Experimental study of shear band formation: Bifurcation and localization

Diffuse bifurcations engraving diverse shear bands in granular materials

Evolution of deformation and breakage in sand studied using X-ray tomography

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