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3D Synchrotron Micro-Computed Tomography (SMT)

X-ray Computed Tomography (CT) has emerged as a powerful, non-destructive scanning technique that can produce 3D rendering of the scanned object. It is a technique in which an incident x-ray beam passes through an object, and the beam is collected with an array of detectors. The object is rotated such that the x-ray beam probes from several angles to collect attenuation data and produce the equivalent of a cross-sectional “slice” through the region of interest. Recently, it was possible to acquire images of meso- or micro-scale properties of soil fabric using industrial x-ray CT systems, microfocus x-ray CT, combinations of optical, x-ray CT and magnetic resonance imaging and SMT.

The 3D Synchrotron Micro-Computed Tomography (SMT) facility produces intense, monochromatic, continuous, and highly collimated beams of hard x-ray with energy ranges from 10 eV to nearly 100 keV; hence, it is capable of yielding high-resolution 3D images. Throughout scanning, the x-ray beam strikes and penetrates the specimen. Some of the x-ray energy is attenuated by the specimen while other energy is transmitted through it. The transmitted x-ray beam is converted to a visible light by a scintillator and captured by a camera system. The light captured by the camera is an image projection of the specimen at one angle. In order to reconstruct a complete scan, several image projections of the sample were taken at different angles from, 0° to 180°. The following Figure shows a schematic of the SMT scanning setup.

(a) Photo of mini-triaxial cell on the stage of Beamline 13 of the Advanced Photon Source (APS), Argonne National Laboratory (APL); (b) Photo of the triaxial cell’)
SMT image of Limestone aggregate
SMT slice through a partially saturated column of Mason sand (gray = sand particles; blue = water; black = air)
Triaxial test on ASTM 20-30 sand (specimen diameter and height are 9.5 mm ~20 mm, respectively)
Typical CT Scans of a microgravity (µg) triaxial experiment taken at 25% Axial Strain
Typical CT Scans of a CTC Experiment taken at 25% Axial Strain
Typical CT Scans of a microgravity (µg) triaxial experiment taken at 25% Axial Strain
Computed tomography (CT) scans of triaxial specimens tested on earth (1g environment)
Photograph of plane-strain experiment after shearing (walls to impose plane-strain condition removed before taking picture)
CT image and void ratio map (at center of specimen) for a plane strain experiment on F-75 Ottawa sand
SMT image of a sub-volume of plane strain experiment on F-75 silica sand (a) Schematic of a profile and a section; (b) segmented cross-section abcd; (c) segmented profile ABCD; (d) void ratio map of abcd; (e) void ratio map of ABCD
SMT image of a plane strain experiment of F-75 sand where the shear band is visible. (a) Segmented CT image ABCD; (b) average particle contacts within sub-volume abcd
SMT image of the shear band within a plane strain experiment of F-75 sand (a) Particle orientations inside shear band illustrated by a few darkened particles; (b) arch-like structures inside the shear band. Post-scanning image editing used to darken particles to highlight column structures

Some of the Related Publications:

  1. Cil, M. B. and Alshibli, K. (2014). “3D Evolution of Sand Fracture Under 1D Compression”, Geotechnique, Vol. 64, No. 5, pp. 351-364, http://www.icevirtuallibrary.com/doi/10.1680/geot.13.P.119
  2. Cil, M. B. and Alshibli, K. A. (2014) “3D Analysis of Kinematic Behavior of Granular Materials in Triaxial Testing Using DEM with Flexible Membrane Boundary”, Acta Geotechnica, Vol. 9, No. 2, pp. 287-298, http://link.springer.com/article/10.1007%2Fs11440-013-0273-0
  3. Hasan, A. and Alshibli, K. A. (2012) “Three Dimensional Fabric Evolution of Sheared Sand”, Granular Matter, Vol. 14, No. 4, pp. 469-482 DOI: http://dx.doi.org/10.1007/s10035-012-0353-0
  4. Hasan, A. and Alshibli, K. A. (2010) “Experimental Assessment of 3D Particle-to-Particle Interaction within Sheared Sand using Synchrotron Microtomography”, Geotechnique, Vol. 60, No. 5, pp. 369-379, DOI: http://dx.doi.org/10.1680/geot.2010.60.5.369
  5. Alshibli, K. A. and Hasan, A. (2008) “Spatial Variation of Void Ratio and Shear Band Thickness in Sand Using X-ray Computed Tomography”, Geotechnique, Vol. 58, No. 4, pp. 249-257, DOI: http://dx.doi.org/10.1680/geot.2008.58.4.249
  6. Alshibli, K.A., Alramahi, B., and Attia, A. M. (2006) “Assessment of Spatial Distribution of Porosity in Synthetic Quartz Cores Using Microfocus Computed Tomography (µCT)”, Particulate Science and Technology: An International Journal, Vol. 24, No. 4., pp. 369-380, DOI: http://dx.doi.org/10.1080/02726350600934606
  7. Alshibli, K.A. and Alramahi, B. (2006) “Microscopic Evaluation of Strain Distribution in Granular Materials during Shear”, ASCE, Journal of Geotechnical & Geoenvironmental Engineering, Vol. 132, No. 1, pp. 80-91, DOI: http://dx.doi.org/10.1061/(ASCE)1090-0241(2006)132:1(80)
  8. Al-Raoush, R. and Alshibli, K. A (2006) “Distribution of Local Void Ratio in Porous Media Systems from 3D X-ray Micro-tomography Images” Physica A: Statistical Mechanics and its Applications, Vol. 361 (March), No. 2, pp. 441-456, DOI: http://dx.doi.org/10.1016/j.physa.2005.05.043
  9. Batiste, S. N., Alshibli, K. A., Sture, S., and Lankton, M. (2004) “Shear Band Characterization of Triaxial Sand Specimens Using Computed Tomography” ASTM, Geotechnical Testing Journal, Vol. 27, No. 6, pp. 568-579, DOI: http://dx.doi.org/10.1520/GTJ12080
  10. Alshibli, K. A., Sture, S., Costes, N. C., Frank, M., Lankton, M., Batiste, S., and Swanson, R. (2000) “Assessment of Localized Deformations in Sand Using x-ray Computed Tomography”, ASTM Geotechnical Testing Journal, Vol. 23, No. 3, pp. 274-299, DOI: http://dx.doi.org/ 10.1520/GTJ11051J

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