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Hall S.A.,Lund University | Hall S.A.,European Spallation Source AB | Desrues J.,Laboratoire | Viggiani G.,Laboratoire | And 2 more authors.
Procedia IUTAM | Year: 2012

This paper outlines some recent advances in the full-field experimental characterisation of the mechanics of granular geomaterials (in particular, sands) using a range of methods that provide characterisation at different scales, from the sample-scale down to the inter-and intra-grain scale. The techniques used are "full-field" approaches involving in-situ x-ray micro-tomography, 3D-volumetric digital image analysis/correlation and grain ID-tracking, in-situ 3D x-ray diffraction and in-situ, spatially-resolved neutron diffraction. These methods provide new data on the mechanics of sand at different scales, including continuum measures of strain, porosity, and fabric plus discrete measures of particle kinematics and force transmission. The results of such measurements might be used to advance higher-order continuum theories, and provide the necessary input parameters, or to calibrate discrete grain-scale simulations of sand behaviour to explore loading paths that are inaccessible in the laboratory. © 2012 Published by Elsevier B.V.


Tengattini A.,University of Sydney | Tengattini A.,University Grenoble Alpes | Das A.,University of Sydney | Nguyen G.D.,University of Adelaide | And 4 more authors.
Journal of the Mechanics and Physics of Solids | Year: 2014

This is the first of two papers introducing a novel thermomechanical continuum constitutive model for cemented granular materials. Here, we establish the theoretical foundations of the model, and highlight its novelties. At the limit of no cement, the model is fully consistent with the original Breakage Mechanics model. An essential ingredient of the model is the use of measurable and micro-mechanics based internal variables, describing the evolution of the dominant inelastic processes. This imposes a link between the macroscopic mechanical behavior and the statistically averaged evolution of the microstructure. As a consequence this model requires only a few physically identifiable parameters, including those of the original breakage model and new ones describing the cement: its volume fraction, its critical damage energy and bulk stiffness, and the cohesion. © 2014 Elsevier Ltd.


Vitone C.,University of Bari | Cotecchia F.,University of Bari | Viggiani G.,Grenoble Institute of Technology | Hall S.A.,Grenoble Institute of Technology | And 2 more authors.
International Journal for Numerical and Analytical Methods in Geomechanics | Year: 2013

This article presents the developments of an ongoing research aimed at modelling the influence of fissuring on the behaviour of clays. In particular, it recalls the main results of an extensive laboratory investigation on a fissured bentonite clay from the south of Italy and presents the data of a new investigation on the evolution with shearing of the strain fields developing within the clay, resulting from Digital Image Correlation (DIC). Element test results are analysed in the framework of continuum mechanics and linked to the clay fissuring features, once characterised using the Fissuring IDentity (F-ID) chart. This article compares the bentonite behaviour with that of other fissured clays of different F-IDs, highlighting the common behavioural features. Thereafter, the soil response at the macro level is related to the DIC-derived strain fields evolving within the clay with loading. For this purpose, DIC was successfully used to investigate the deformation processes active in the fissured clay and the sources of the localisation phenomena. DIC is shown to provide indications of the extent to which highly to medium fissured clays element test results can be of use to model the clay behaviour according to continuum mechanics. © 2012 John Wiley & Sons, Ltd.


Ando E.,Grenoble Institute of Technology | Viggiani G.,Grenoble Institute of Technology | Hall S.A.,Lund University | Hall S.A.,European Spallation Source AB | Desrues J.,Grenoble Institute of Technology
Geotechnique Letters | Year: 2013

Combining x-ray tomography and three-dimensional (3D) image analysis has finally opened the way for experimental micro-(geo)mechanics, allowing access to different scales of interest. When these correspond to a scale that has been imaged at high spatial resolution, high-quality measurements can be obtained (e.g. 3D displacements and rotations of individual grains of sand sample under load). However, there are issues when the scale of interest is smaller, for example the characterisation of grain-to-grain contacts (their orientations and evolution) or production of fines by grain breakage. This paper presents a short selection of new grain-scale measurements obtained using existing techniques. The challenges associated with smaller scale measurements on the same images are also discussed through a few examples from ongoing work.


Hall S.A.,Lund University | Hall S.A.,European Spallation Source AB
Geophysical Research Letters | Year: 2013

The challenge of understanding how localized deformation modifies fluid flow in porous rock is addressed. New approaches are presented, based on neutron radiography and digital image analyses, to track fluid flow in rock specimens and to calculate flow velocity fields providing local flow measurements. The results show that neutron radiography, backed up by appropriate image analysis, is a very powerful tool in this context, being far more sensitive to the fluids in the rock than X-ray radiography. Analysis of neutron radiography images of water imbibition into a laboratory-deformed sandstone specimen has provided new measurements of local fluid flow velocities within a shear band, indicating that flow is faster and water storage is higher in the band (attributed to higher capillary forces associated with damage). © 2013 American Geophysical Union. All Rights Reserved.


Ando E.,Grenoble Institute of Technology | Hall S.A.,Lund University | Hall S.A.,European Spallation Source AB | Viggiani G.,Grenoble Institute of Technology | And 2 more authors.
Geotechnique Letters | Year: 2012

Strain localisation plays a key role in the deformation of granular materials. Such localisation involves bands of just a few grains wide, which dominate the material's macroscopic response. This grain-scale phenomenon presents challenges for continuum modelling, which is the rationale behind models that explicitly take micro-scales into account. These in turn require micro-scale experimental analysis. In this work, X-ray tomography is used to image a small sample of oolitic sand while it deforms under triaxial compression. Grains are followed with a technique combining recent developments in image correlation and particle tracking. From these rich data, the evolution of the material in a subvolume of a thousand grains inside the sample (which contains 53 000 grains) is presented. The subvolume is chosen to lie inside the shear band that appears at the sample scale. Three-dimensional (3D) grain kinematics are analysed in three increments: the beginning of the test, the peak of the sample's macroscopic axial stress response and the residual stress state. When the sample's deformation is homogeneous (increment one) or fully localised (increment three), the kinematics of the grains in the subvolume appear to be representative of the kinematics occurring at the sample scale, allowing micro-mechanical observations to be made. In the transition from homogeneous to localised deformation (increment two), however, the scale of observation requires a zoom out of the subvolume to the sample scale in order to capture the complex mechanisms at play.


Ainsworth R.,Royal Holloway, University of London | Molloy S.,European Spallation Source AB
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2014

The European Spallation Source (ESS) linac will consist of three families of superconducting RF cavities to accelerate protons to a final beam energy of 2.5 GeV for collision with the target. Beam induced HOMs in these cavities may drive the beam unstable and increase the cryogenic load, severely limiting the operation of the linac. The effect of these modes on the beam quality is investigated in detail using a numerical code dedicated to beam-HOM interaction. © 2012 Elsevier B.V.


Raymond S.,Joseph Fourier University | Kaneko K.,Japan Atomic Energy Agency | Hiess A.,European Spallation Source AB | Steffens P.,Laue Langevin Institute | Lapertot G.,Joseph Fourier University
Physical Review Letters | Year: 2012

Polarized inelastic neutron scattering under a magnetic field is used to get a microscopic insight into the spin resonance of the heavy fermion superconductor CeCoIn5. The resonance line shape is found to depend on the neutron polarization: Some of the spectral weight is common to the two polarization channels while the remaining part is distributed equally between them. This is evidence for the spin resonance being a degenerate mode with three fluctuation channels: A Zeeman split contribution and an additional longitudinal mode. © 2012 American Physical Society.


Yeck J.,European Spallation Source AB
IPAC 2014: Proceedings of the 5th International Particle Accelerator Conference | Year: 2014

This paper evaluates the driving forces behind big science projects. The paper should be useful to organizations and individuals participating in big science projects or wanting to make business with such projects. Copyright © 2014 CC-BY-3.0 and by the respective authors.


Hilger A.,Helmholtz Center Berlin | Kardjilov N.,Helmholtz Center Berlin | Manke I.,Helmholtz Center Berlin | Zendler C.,Helmholtz Center Berlin | And 5 more authors.
Optics Express | Year: 2015

A neutron transport system for the planned imaging instrument ODIN at the future European Spallation Source (ESS) based on neutron optical components was designed and optimized. Different ways of prompt pulse suppression were studied. The spectral performance of the optimal neutron guide configuration is presented. In addition, the influence of the gaps in the guide system needed for the required chopper configuration was investigated. Given that the requirements for an imaging instrument located on a long guide system and hosting a complex chopper system are extremely demanding in terms of spectral and divergence needs, this study can be beneficial for a wide range of instruments in various ways. © 2015 Optical Society of America.

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