ORCID Profile
0000-0001-5509-5287
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Publisher: IOP Publishing
Date: 29-07-2015
Publisher: Elsevier BV
Date: 05-2018
Publisher: Elsevier BV
Date: 05-2023
Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D2SM00322H
Abstract: X-ray tomography study of the link between particle and macroscopic behaviour of an hygroscopic material. Its microstructure ( e.g., contact area and orientation) is characterised and the deformation of particles quantified and linked to water content.
Publisher: Copernicus GmbH
Date: 04-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-9048
Abstract: & & The localisation of structural damage, in the form of faults and fractures, along a distinct and emergent fault plane is the key driving mechanism for catastrophic failure in the brittle Earth. However, due to the speed at which stable crack growth transitions to dynamic rupture, the precise mechanisms involved in localisation as a pathway to fault formation remain unknown. Understanding these mechanisms is critical to understanding and forecasting earthquakes, including induced seismicity, landslides and volcanic eruptions, as well as failure of man-made materials and structures. We used time-resolved synchrotron x-ray microtomography to image in-situ damage localisation at the micron scale and at bulk axial strain rates down to 10& sup& -7& /sup& s& sup& -1& /sup& . By controlling the rate of micro-fracturing events during a triaxial deformation experiment, we deliberately slowed the strain localisation process from seconds to minutes as failure approached. This approach, originally established to indirectly image fault nucleation and propagation with acoustic emissions, is completely novel in synchrotron x-ray microtomography and has enabled us to image directly processes that are normally too transient even for fast synchrotron imaging methods. Here, we first present the experimental apparatus and control system used to acquire the data, followed by damage localisation and shear zone development in a s le of Clashach sandstone viewed in unprecedented detail. Time-resolved microtomography images demonstrate a strong intrinsic correlation between shear and dilatant strain in the localised zone, with bulk shear strain accomodated by the nucleation and rotation of en-echelon tensile microcracks within a grain-scale shear band. Rotation is accompanied by antithetic to synthetic shear sliding of neighbouring crack surfaces as they rotate. The evolving 4D strain field, measured with incremental digital volume correlation between pairs of recorded x-ray tomographic volumes, independently confirm the correlation between shear and dilatant strain and show how strain localises spontaneously, first through exploration of several competing shear bands at peak stress before transitioning to failure along the optimally-oriented final fault plane. In order to & #8216 ground-truth& #8217 inferences made from bulk measurements and seismic waves (the primary method of detecting deformation at the field-scale where direct imaging of the subsurface is impossible), we (a) compare rupture energy estimates from local slip measurements with those from bulk slip data, and (b) use AE source location estimates to identify in idual cracks and other local changes in the microstucture that may explain the AE source.& &
Publisher: Thomas Telford Ltd.
Date: 12-2018
Abstract: Hydraulic fracturing, the creation of fractures by high-pressure fluid injection into a solid medium, is of interest to enhance the permeability of rocks. This complex three-dimensional hydro-mechanical process, however, has only been studied in the laboratory by boundary measurements or acoustic techniques with low spatio-temporal resolutions until now. In this paper, direct, high spatial resolution, and near real-time visualisation results of hydraulic fracture generation and propagation in prismatic specimens of Marcellus shale rock under in situ conditions (70 MPa, plane strain) are presented. Poly-methyl methacrylate specimens are also tested under the same conditions to highlight the importance of rocks' internal structure on the response of the tested rock. The results reveal a complex interaction among the injected fluid, the pre-existing natural fractures in shale structure, and the hydraulically induced fracture highlighting the governing role of rock fabric even under high stresses. These measurements are possible due to the unique sensitivity of neutrons to water. Besides the intrinsic interest of the results presented, this exploratory investigation highlights the potential of neutron imaging in elucidating the evolution of fluid flow and fluid-driven fractures, as X-rays have done for the evolution of solid structure only. Further, understanding of the mechanics of fracking will lead to development of more accurate hydro-mechanical constitutive models thus enabling the design of field operations with higher efficiencies.
Publisher: Elsevier BV
Date: 05-2021
Publisher: Copernicus GmbH
Date: 04-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-15691
Abstract: & & Catastrophic failure is a critical phenomenon present in Earth systems on a variety of scales, and is associated with the evolution of damage leading to system-size failure. Laboratory testing of rock failure permits characterization of fracture network evolution at the micro-scale to understand the interaction of cracks, pores and grain boundaries to an applied stress field, and the relationship between deformation and seismic response. Previous studies have relied on acoustic emissions (hearing) or X-ray imaging (seeing) to study the process of localization, which involves spontaneous self-organization of smaller cracks along faults and fractures on localised zones of deformation. To combine hearing and seeing of the microscopic processes and their control of system-sized failure, a novel x-ray transparent cell was used for deformation experiments of rock s les, which permits integration of acoustic monitoring with fast synchrotron x-ray imaging. To increase temporal characterization of damage beyond the temporal resolution of the fast 3D synchrotron system, acoustic emission (AE) feedback control was used to regulate the applied stress and slow down the deformation processes. As a result, there is increased temporal resolution of the incremental deformation between successive x-ray scanned states allowing synchronized comparison of acoustic emissions to x-ray scans. Here, we present the seismic analysis used to characterize the velocity evolution of the rock s les, and the location and characteristics of in idual AE events in relation to microscopic deformation processes. Time-lapse velocity measurements are linked to internal stress changes and structural damage corresponding to seismic and aseismic deformation processes, while acoustic emissions are a direct indication of local cracking.& We show that we can successfully locate AE events in 3D using only two sensors on either end of the s le, based on ellipsoid mapping, and x-ray image to event correlation. We explore temporal and spatial statistics of AE signatures and how those are linked to the strain field in the s les measured with incremental digital volume correlation between pairs of recorded x-ray tomograms. The direct observation of AE and X-ray images enables quantification of relevant seismic (local cracking leading to AE) to aseismic (elastic loading and silent irreversible damage) processes, with information extracted over fine temporal resolution throughout the deformation process through the AE-feedback control.& &
Publisher: Springer Science and Business Media LLC
Date: 12-03-2018
Publisher: Copernicus GmbH
Date: 28-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-8048
Abstract: & & Tectonic-scale features happening at convergent plates are ultimately the outcome of microscopic, grain scale processes. In collision zones, prograde metamorphism occurs by gradual increase of pressure and temperature [1 2]. Among the most important prograde mineral reactions are dehydration reactions, which are characterized by solid volume reduction, porosity creation, fluid release and high pore fluid pressures [3]. Most models linking dehydration and mechanical instabilities [4-6] involve feedback loops between coupled chemical, hydraulic and mechanical processes. Feedbacks control pore fluid pressure build-up and drainage, and provide efficient pathways for the transport of chemical components. Gypsum dehydration is crucial in the formation of detachment faults thin-skinned tectonics [7]. It is also used as a proxy for serpentine dehydration and the generation of intermediate depth seismic events/aseismic slip activity [8].& & & & We performed a set of experimental gypsum dehydrations both at the TOMCAT microtomography beamline at the Swiss Light Source, and in the laboratory. Using a modified version of the Mjolnir triaxial rig [9] that allowed control of pore fluid pressure in the synchrotron microtomography setup enabled us to document how differential stress (& #8710 & #963 ) and pore fluid pressure (P& sub& f& /sub& ) influence the dehydration of Volterra alabaster gypsum to bassanite at a constant confining pressure and temperature in 4D.& & & & We derived data on mineral phase transformation and formation of pore networks by applying a deep-learning algorithm in ORS Dragonfly& #174 software, which reduced data processing times, minimized interpretation biases, and allowed analysing larger volumes. The results exhibit an extremely high accuracy compared to standard procedures. The analysis of phase proportions (gypsum, bassanite and porosity) of segmented volumes correlates very well to theoretical predictions indicating a correct segmentation from the algorithms and self-consistency of the generated datasets. Comparing results obtained& at various & #8710 & #963 and P& sub& f& /sub& to the light of mechanical data and additional in-house experiments allows us to better interpret their effect on reaction duration, magnitude and textural evolution of the rock. Transient phenomena as well as in idual grain transformation and growth are now traceable in a fully automated way.& & & & Our data further our understanding of gypsum dehydration: We found that & #8710 & #963 greatly influences the assemblage of the bassanite needles, which tend to grow nearly vertical at & #8710 & #963 & #8773 0. Increasing & #8710 & #963 significantly increases s le compaction. On the contrary, increasing P& sub& f & /sub& decreases the bulk deformation and slows down the reaction. As pores grow around bassanite needles, the control of the orientation of needles by differential stress can influence the overall pore network and thus introduce anisotropies during transient and final stages of the reaction. Our data confirm that & #8710 & #963 and P& sub& f& /sub& greatly influence transient and final rock texture, which has implications on drainage during nappe emplacements.& & & & & strong& References& /strong& : [1] Hacker et al., 2003, /10.1029/2001JB001129 [2] Peacock, 2001, 10.1130/0091-7613(2001)029& :ATLPOD& .0.CO [3] Llana-Funez et al. 2012, /10.1007/s00410-012-0726-8 [4] Raleigh and Paterson, 1965 /10.1029/JZ070i016p03965& [5] Dobson et al., 2002 /10.1126/science.1075390 [6] Jung et al., 2004 /10.2747/0020-6814.46.12.1089 [7] Hubbert and Rubey, 1959 /10.1130/0016-7606(1959)70[115:ROFPIM]2.0.CO [8] Rutter et al. 2009 /10.1016/j.jsg.2008.09.008 [9] Butler 2020, /10.1107/S160057752001173X.& &
Publisher: Copernicus GmbH
Date: 21-06-2021
DOI: 10.5194/SE-2021-83
Abstract: Abstract. Phyllosilicates are generally regarded to have a reinforcing effect on chemical compaction by dissolution-precipitation creep (DPC) and thereby influence the evolution of hydraulic rock properties relevant to groundwater resources, geological repositories as well as fossil fuel reservoirs. We conducted oedometric compaction experiments on layered NaCl-biotite s les to test this assumption. In particular, we aim to analyse slow chemical compaction processes in the presence of biotite on the grain scale and determine the effects of chemical and mechanical feedbacks. We used time-resolved (4D) microtomographic data to capture the dynamic evolution of the transport properties in layered NaCl-NaCl/biotite s les over 1619 and1932 hours of compaction. Percolation analysis in combination with advanced digital volume correlation techniques showed that biotite grains influence the dynamic evolution of porosity in the s le by promoting a reduction of porosity in their vicinity. However, the lack of preferential strain localisation around phyllosilicates and a homogeneous distribution of axial shortening across the s le suggests that the porosity reduction is not achieved by pore collapse but by the precipitation of NaCl sourced from outside the NaCl/biotite layer. Our observations invite a renewed discussion of the effect of phyllosilicates on DPC, with a particular emphasis on the length scales of the processes involved. We propose that, in our experiments, the diffusive transport processes invoked in classical theoretical models of DPC are superseded by chemo-mechanical feedbacks that arise on longer length scales. These feedbacks drive NaCl diffusion from the marginal pure NaCl layers into the central NaCl-biotite mixture over distances of several hundredμm and several grain diameters. Such a mechanism was first postulated by Merino et al. (1983)
Publisher: The Open Journal
Date: 13-07-2020
DOI: 10.21105/JOSS.02286
Publisher: Elsevier BV
Date: 02-2015
Publisher: Copernicus GmbH
Date: 10-01-2022
Abstract: Abstract. Phyllosilicates are generally regarded to have a reinforcing effect on chemical compaction by dissolution–precipitation creep (DPC) and thereby influence the evolution of hydraulic rock properties relevant to groundwater resources and geological repositories as well as fossil fuel reservoirs. We conducted oedometric compaction experiments on layered NaCl–biotite s les to test this assumption. In particular, we aim to analyse slow chemical compaction processes in the presence of biotite on the grain scale and determine the effects of chemical and mechanical feedbacks. We used time-resolved (4-D) microtomographic data to capture the dynamic evolution of the porosity in layered NaCl–NaCl/biotite s les over 1619 and 1932 h of compaction. Percolation analysis in combination with advanced digital volume correlation techniques showed that biotite grains influence the dynamic evolution of porosity in the s le by promoting a reduction of porosity in their vicinity. However, the lack of preferential strain localisation around phyllosilicates and a homogeneous distribution of axial shortening across the s le suggests that the porosity reduction is not achieved by pore collapse but by the precipitation of NaCl sourced from outside the NaCl–biotite layer. Our observations invite a renewed discussion of the effect of phyllosilicates on DPC, with a particular emphasis on the length scales of the processes involved. We propose that, in our experiments, the diffusive transport processes invoked in classical theoretical models of DPC are complemented by chemo-mechanical feedbacks that arise on longer length scales. These feedbacks drive NaCl diffusion from the marginal pure NaCl layers into the central NaCl–biotite mixture over distances of several hundred micrometres and several grain diameters. Such a mechanism was first postulated by Merino et al. (1983).
Publisher: Copernicus GmbH
Date: 21-06-2021
Publisher: Elsevier BV
Date: 11-2018
Publisher: IOP Publishing
Date: 08-06-2021
Abstract: The measurement of the position of single-sized spheres in 3D from a single, ergent, radiographic projection is addressed in the present study with the development of a novel method. Generally speaking, the location of the shadow cast by a single sphere on a detector defines a source-detector ray the position of the particle along this ray is identified by the strong prior knowledge of its radius and the size of the shadow. For a dense assembly of equal-sized particles whose projections overlap, a novel Fourier transform based technique is introduced to give a first 3D determination of the particle centres. The uncertainty of this measurement is calculated from synthetic data with a known noise distribution. A further refinement of this measurement is performed based on the minimisation of the projection residual. The combined approach is validated both on synthetic data, and on real radiographs of a glass bead packing. The effect of noise on the measurement uncertainty is evaluated. The technique is made available to the community in the open source python package radioSphere .
Publisher: Springer International Publishing
Date: 30-12-2014
Publisher: The Royal Society
Date: 08-04-2013
Abstract: Complex systems techniques are used to analyse X-ray micro-CT measurements of grain kinematics in Hostun sand under triaxial compression. Network nodes with the least mean shortest path length to all other nodes, or highest relative closeness centrality, reside in the region where the persistent shear band ultimately develops. This trend, whereby a group of grains distinguishes themselves from the rest in the s le, remarkably manifests from the onset of loading. The shear band's boundaries and thickness, evident from the network communities' borders and essentially constant mean size, provide corroborating evidence of early detection of strain localization. Our findings raise the possibility that the formation and the location of the persistent shear band may be decided in the nascent stages of loading, well before peak shear stress. Grain-scale digital image correlation strain measurements and statistical tests confirm the results are robust. Moreover, the trends are unambiguously reproduced in a discrete element simulation of plane strain compression.
Publisher: Springer International Publishing
Date: 30-12-2014
Publisher: IOP Publishing
Date: 07-07-2021
Abstract: The bone tissue formed at the contact interface with metallic implants, particularly its 3D microstructure, plays a pivotal role for the structural integrity of implant fixation. X-ray tomography is the classical imaging technique used for accessing microstructural information from bone tissue. However, neutron tomography has shown promise for visualising the immediate bone-metal implant interface, something which is highly challenging with x-rays due to large differences in attenuation between metal and biological tissue causing image artefacts. To highlight and explore the complementary nature of neutron and x-ray tomography, proximal rat tibiae with titanium-based implants were imaged with both modalities. The two techniques were compared in terms of visualisation of different material phases and by comparing the properties of the in idual images, such as the contrast-to-noise ratio. After superimposing the images using a dedicated image registration algorithm, the complementarity was further investigated via analysis of the dual modality histogram, joining the neutron and x-ray data. From these joint histograms, peaks with well-defined grey value intervals corresponding to the different material phases observed in the specimens were identified and compared. The results highlight differences in how neutrons and x-rays interact with biological tissues and metallic implants, as well as the benefits of combining both modalities. Future refinement of the joint histogram analysis could improve the segmentation of structures and tissues, and yield novel information about specimen-specific properties such as moisture content.
Location: Switzerland
No related grants have been discovered for Edward Andò.