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| Titel |
Damage localisation and fracture propagation in granite: 4D synchrotron
x-ray microtomographic observations from an in-situ triaxial deformation
experiment at SOLEIL |
| VerfasserIn |
Alexis Cartwright-Taylor, Florian Fusseis, Ian Butler, Michael Flynn, Andrew King |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250152651
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| Publikation (Nr.) |
 EGU/EGU2017-17515.pdf |
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| Zusammenfassung |
| To date, most studies of damage localisation and failure have utilised indirect techniques to
visualise the pathway to failure. The advent of synchrotron tomography and x-ray
transparent experimental cells provides for the first time the opportunity to image
localisation and fracture propagation in-situ, in real time with spatial resolutions of a few
microns.
We present 4D x-ray microtomographic data collected during a triaxial deformation
experiment carried out at the imaging beamline PSICHE at the French Synchrotron SOLEIL.
The data document damage localisation and fracture propagation in a microgranite. The
sample was deformed at 15 MPa confining pressure and 3x10−5 s−1 strain rate, in a novel,
miniature, x-ray transparent, triaxial deformation apparatus, designed and built at the
University of Edinburgh. We used a 2.97 mm diameter x 9.46 mm long cylindrical sample of
Ailsa Craig microgranite, heat treated to 600 ˚ C to introduce flaws in the form of pervasive
crack damage. As the sample was loaded to failure, 21 microtomographic volumes were
acquired in intervals of 5-20 MPa (decreasing as failure approached), including one scan at
peak differential stress of 200 MPa (1.4 kN end load) and three post-failure scans. The
scan at peak stress contained the incipient fault, and the sample failed immediately
when loading continued afterwards. During scanning, a constant stress level was
maintained. Individual datasets were collected in ∼10 minutes using a white beam with
an energy maximum at 66 keV in a spiral configuration. Reconstructions yielded
image stacks with a dimension of 1700x1700x4102 voxels with a voxel size of 2.7
μm.
We analysed damage localisation and fracture propagation in the time series data.
Fractures were segmented from the image data using a Multiscale Hessian fracture filter [1]
and analysed for their orientations, dimensions and spatial distributions and changes in these
properties during loading. Local changes in volumetric and shear strains between
time steps were quantified using 3D digital image correlation [2]. In combination,
these analyses show the extent and evolution of local aseismic deformation and that
related to microcracking. Our results provide direct evidence of ongoing deformation
processes such as micro-fracture nucleation at pre-existing flaws, in the form of cracks,
grain boundaries and pores, and coalescence of en-echelon tensile micro-fractures
along a shear fault in response to changes in the local stress field. These direct 4D
observations of damage evolution and strain localisation complement the seminal
results of Lockner et al. [3], who first imaged the process of fault growth using
acoustic emissions locations. Our data provide further insight into the aseismic
mechanisms that dissipate 99% of the total accumulated strain energy [4] and the
interactions between these mechanisms and the developing microcracks. Our results also
provide experimental verification of models for shear fracture formation whereby
pre-existing flaws become connected by en-echelon tensile cracks that extend from their
edges.
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[1] Voorn et al., 2015, J. Petroleum Sci. Eng. 127, 270-285.
[2] Hall, S. et al., 2010, Geotechnique 60, 315-322.
[3] Lockner, D., et al., 1991, Nature 350, 39-42.
[4] Byerlee, J., 1993, Geology 21, 303-306. |
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