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

Abstract

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.

Effect of particle morphology and contacts on particle breakage in a granular assembly studied using X-ray tomography

“…This paper aims to make several contributions. Encouraged by the success of X-ray tomography in revealing particle rearrangements during shearing tests (e.g., [26][27][28][29]), as well as revealing some parts of breakage processes at higher mean stresses (e.g., [30][31][32][33][34][35][36]), we present our findings regarding the onset of particle breakage, deriving from our study of 3D images of a dry granular assembly undergoing crushing. Specifically, strain controlled oedometric compression tests were carried out on an assembly of zeolite granules, while performing X-ray tomography, focusing on the initial stages of particle breakage.…”

The mechanics of brittle granular materials with coevolving grain size and shape

“…At this juncture, an open area of research not explored in this work is how the inevitable statistical disorder of the particle shapes within granular materials influences the link between grain-scale and continuum-scale properties. From this standpoint, considerable assistance may derive from the combination of the proposed continuum framework with multi-scale characterization technologies based on digital imaging and high-resolution X-ray tomography, through which particle irregularities can be detected down to sub-micrometre scales, including alterations caused by grain crushing [8,60].…”

“…In return, this impacts local and collective processes ranging from contact deformation and grain fracture to volume change and critical density-stress state relationships [5][6][7]. Novel digital imaging techniques have greatly expanded our ability to examine initial and evolving particle shapes, with major benefits for the in situ characterization of continuum-scale processes [8][9][10]. Similarly, computational advances have allowed us to replicate complex particle shapes through geometric analogues ranging from sphere clumps [11] to polyhedra [12], ellipsoids [13] or level sets [14], with corresponding benefits for the study of particle fracture and shape evolution [15][16][17].…”

Using Synchrotron-Based X-Ray Microcomputed Tomography to Characterize Water Distribution in Compacted Soils

“…In traditional soil mechanics and engineering practice, research related to the microstructure of soils was mostly limited to two-dimensional (2D) distribution of soil particles and voids generally using scanning electron microscope and mercury intrusion porosimetry [1][2][3]. With the development of technology, the X-ray μ-CT has recently been proved to be effective in 3D characterization of soils, and it has been used (i) to quantify the porosity or voids [4][5][6][7][8][9][10][11][12][13][14], (ii) to investigate the strain localization (e.g., [15][16][17][18][19][20][21][22]), (iii) to characterize the particle breakage (e.g., [15,[23][24][25][26][27]), (iv) to investigate the particle morphology and orientation [28][29][30][31], and (v) to estimate the particle strains and rotations [17,25,[32][33][34][35][36][37]. e main parameters of the X-ray μ-CT tests are presented in Table 1, showing very interesting features in terms of resolution, total acquisition time, and sample size for different materials.…”