Modeling of corrosion-induced cracking is limited by lacking knowledge on the behavior of corrosion products. In this work, the corrosion and cracking processes were experimentally investigated in 3D ...at two different stages. The processes were measured at micro-structural scale, applying nondestructive neutron and X-ray computed tomography in two scans at different stages in the corrosion process. A method to evaluate the average volumetric strain of the compressed corrosion layer was proposed and displacements in the concrete matrix were measured. Strain localization revealed cracks not directly visible in the images. Multimodal tomography demonstrated to be an effective method for investigating steel corrosion in reinforced concrete.
•Multimodal tomography is a powerful method for measuring steel corrosion in concrete.•A method to evaluate the average volumetric strain of compressed corrosion was proposed.•Strain localization was captured in correspondence to the crack pattern.
Neutron imaging for geomechanics: A review Tengattini, Alessandro; Lenoir, Nicolas; Andò, Edward ...
Geomechanics for energy and the environment,
September 2021, 2021-09-00, Letnik:
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Journal Article
Odprti dostop
During the last few decades, a number of advanced experimental techniques have provided an unprecedented insight into the behaviour of geomaterials. A notable example are the so-called full-field ...techniques such as x-ray and neutron imaging, which allow the non destructive characterisation of the 4D (3D+time) response of geomaterials undergoing hydro–chemo–thermo-mechanical loading. While x-ray tomography has over the last decade become a pillar in the domain, neutron imaging remains a relatively less known tool. The unique properties of a neutron beam, such as high sensitivity to hydrogen (e.g., water, hydrocarbons), high penetration into metals (allowing the imposition of extreme boundary conditions), and isotope sensitivity (e.g., D2O/H2O), make neutron imaging an extremely interesting tool for experimental geomechanics.
This paper reviews the contribution of neutron imaging to geomechanics. A particular focus is given to the potential of some very recent developments, such as the combination with simultaneous x-rays and substantial improvements in spatial and temporal resolution.
•Review Paper about the use of Neutron radiography and tomography in geomechanics.•Outlines fundamentals and facilities for neutron imaging, comparing it to x-rays.•Historical background, recent achievements and use for in-operando testing.•Reviews recently developed simultaneous x-ray/neutron imaging, and its use.
Understanding the migration of high-temperature fluids through the porous medium of cement-based materials has a pivotal role in many engineering applications. The space and time evolution of the ...free water content and the crack network in these materials creates a complex migration process. In this work, we experimentally investigate water vapour migration in pre-cracked porous media of dry and saturated initial saturation states. Besides studying the mean temperature and pressure evolution, we quantify the rapid spatial distribution of the condensed water operando through high-speed neutron radiography. The associated physical phenomena for the condensed water migration into the porous media is reported one order of magnitude stronger in the dry sample. Combined features of neutron and x-ray tomographies enable the 3D quantification of condensed water distribution. This unique data set aims to provide a novel database for the multi-physics modelling of two-phase fluid flow in cracked media for varying initial saturation.
When exposed to high temperatures, concrete is prone to explosive spalling, resulting in the projection of concrete flakes and the reduction of the structural element cross-section. Elastic energy ...alone cannot justify the explosive nature of the process: accumulated thermal energy serves as a supplementary source, together with the water in the pores, which can generate kinetic energy through vaporization. The objective of this paper is to study the fast thermal and hygral transients occurring upon depressurization of an internal interface, emulating a crack developing in hot moist concrete. One possible mechanism that could justify this contribution is the flash vaporization of water. This paper presents a new experimental approach to directly measure flash vaporization through rapid-neutron imaging. Additionally, a thermo-hygral model assesses key parameters influencing fast-transient phenomena. Experimental observations reveal moisture loss in a 1-mm-thick layer, equating to a 90 °C temperature drop, justifying a significant amount of released energy.
Here, we report on a new record in the acquisition time for fast neutron tomography. With an optimized imaging setup, it was possible to acquire single radiographic projection images with 10 ms and ...full tomographies with 155 projections images and a physical spatial resolution of 200 µm within 1.5 s. This is about 6.7 times faster than the current record. We used the technique to investigate the water infiltration in the soil with a living lupine root system. The fast imaging setup will be part of the future NeXT instrument at ILL in Grenoble with a great field of possible future applications.
Particle shape affects the mechanical behavior of crushable granular media, especially in the context of phenomena such as impact and penetration. However, shape descriptors are rarely incorporated ...into fracture criteria for single grains, which focus instead on size effects and assume idealized spherical geometries. This study aims to extend multiple frameworks used to predict the crushing resistance of individual sand grains by incorporating the effect of particle shape. We conducted an experimental study for varying grain geometries, as revealed by x-ray tomography, and propose a series of analytical models incorporating the grains’ aspect ratio, computed by ellipsoidal approximation fitting. Specifically, non-spherical shape descriptors are incorporated into different contact laws, fracture criteria, and statistical failure models providing closed-form expressions of the strength of single particles as a function of their size and shape. We compare the performance of these models and assess their accuracy against a series of compression experiments on Ottawa sand grains. Experimentally, we find that elongated grains tend to break at lower compression stress than spherical particles of equal size and that their strength depends more on their shape than on their size. By comparing the performance of the proposed models, it was found that the modified Weibull model for non-spherical grains provides the best overall performance. However, the proposed centre crack model for ellipsoidal grains was found to have a similarly satisfactory ability to capture the experimental evidence, while requiring a simpler parameter calibration procedure. By providing criteria to rationalize and predict the effect of the shape on the crushing resistance of single particles, these results offer an analytical foundation to model shape-dependent particle strength in discrete and continuum models for particle crushing which require this quantity as an input for their analyses.
Graphical abstract
Abstract
The elucidation of lithium ion transport pathways through a solid electrolyte separator is a vital step toward development of reliable, functional all‐solid‐state batteries. Here, advantage ...has been taken of the significantly higher neutron attenuation coefficient of one of the most abundant stable isotopes of lithium,
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Li, with respect to that of naturally occurring lithium isotope mixture, to perform neutron imaging on a purpose built all‐solid‐state lithium–sulfur battery. Increasing the
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Li content in the anode while using natural lithium in the solid electrolyte separator and the cathode enhances the contrast such that it is possible to differentiate, during the initial discharge, between the mobile lithium ions diffusing through the cell from the anode and those that are initially located in the solid electrolyte. The sensitivity of neutrons to the different lithium isotopes means that operando neutron radiography allows demonstration of the lithium ion diffusion through the cell while in situ neutron tomography has permitted presentation, in three dimensions, of the distribution of the trapped lithium ions inside the cell in charged and discharged states.
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