Summary
Modelling the physical behaviour of fibrous materials still remains a great challenge because it requires to evaluate the inner structure of the different phases at the phase scale (fibre or ...matrix) and the at constituent scale (fibre). X‐ray computed tomography (CT) imaging can help to characterize and to model these structures, since it allows separating the phases, based on the grey level of CT scans. However, once the fibrous phase has been isolated, automatically separating the fibres from each other is still very challenging. This work aims at proposing a method which allows separating the fibres and localizing the fibre–fibre contacts for various fibres geometries, that is: straight or woven fibres, with circular or non‐circular cross sections, in a way that is independent of the fibres orientations. This method uses the local orientation of the structure formed by the fibrous phase and then introduces the misorientation angle. The threshold of this angle is the only parameter required to separate the fibres. This paper investigates the efficiency of the proposed algorithm in various conditions, for instance by changing the image resolution or the fibre tortuosity on synthetic images. Finally, the proposed algorithm is applied to real images or samples made up of synthetic solid fibres.
This article aims to discuss and complete the avalanche representations of the failure process of quasi-brittle materials. Paper was used as a model material. We proposed an original method to ...determine avalanches extracted directly from the force drops in the post-peak regime of experimental force–displacement curves. We studied the avalanche distributions on notched and unnotched samples, taking into account the measurement noise. From these experimental tests, two regimes in the avalanche distribution were observed during the propagation of a macrocrack, in particular with a well-defined power law at small scale, that was consistent with other avalanche distributions based on other methods and other materials in literature. A single regime power-law distributed was found for a diffuse damage (without a significant macrocrack propagation) using the Mazars’ damage model. Our results showed that the post-peak regime of tensile curves contained the statistical signature of the propagation of a macrocrack during the rupture of paper.
Wool is considered to possibly exhibit antibacterial properties due to the ability of wool clothing to reduce the build-up of odor, which arises from the microbial activity of skin microbiota. ...Indeed, when tested with a widely used agar diffusion plate test method, even wool or other textiles not treated with any antimicrobial agent can be interpreted to show certain antibacterial effects due to the lack of growth under the specimen, as instructed in ISO 20645:2004 standard. Therefore, we analyzed in detail what happens to bacterial cells in contact with untreated wool and cotton fabric placed on inoculated agar plates by counting viable cells attached to the specimens after 1 and 24 h of contact. All wool and several cotton samples showed no growth under the specimen. Nevertheless, it was shown without a doubt that neither textile material kills bacteria or inhibits cell multiplication. A reasonable explanation is that bacterial cells firmly attach to wool fibers forming a biofilm during multiplication. When the specimen was lifted off the nutrient agar surface, the cells in the form of biofilm remained attached to the wool fibers, removing the biomass and resulting in a clear, no growth zone underneath it. By imaging the textile specimens with X-ray microtomography, we concluded that the degree of attachment could be dependent on surface topography. The results indicate that certain textiles, in this case, wool, could exhibit antibacterial properties by removing excess bacteria that grow on the textile/skin interface when taken off the body.
Mechanical properties of fiber-based materials, such as paper, are governed by the heterogeneous microstructure induced by the formation process. For example, in paper materials during tensile tests, ...lower strains are observed in the flocs (fiber aggregates where the basis weight is larger than the average one) than in the antiflocs (complement of flocs). To explain such behavior, we investigated the mechanical and structural properties of both flocs and antiflocs. Using tensile tests on flocs and antiflocs, we measured their elastic modulus and found that the elastic modulus of flocs was larger than the antiflocs’ one. To understand these differences, a multiscale structural analysis was conducted on 3D X-ray images of flocs and antiflocs at two different spatial resolutions. We found that the floc was thicker than the antifloc, whereas the microscale analysis showed the studied floc and antifloc exhibited the same bulk porosity. Then, it was concluded that the difference in elastic modulus between flocs and antiflocs is mainly due to their thickness difference.
Graphical abstract
Characterising bacterial biofilm growth in porous media is important for developing reliable numerical models of biofouling in industrial biofilters. One of the promising imaging methods to do that ...has been a recent successful application of X‐ray microtomography. However, this technique requires a contrast agent (1‐chloronaphtalene, for example) to distinguish biofilm from the liquid phase, which raises concern about biofilm disruption and impaired image interpretation. To overcome these drawbacks, we tested a new approach based on neutron tomography (NT), which does not need a contrast agent, by imaging two types of porous media (polytetrafluoroethylene – PTFE – and clay beads of various diameters) in glass or PTFE tubes in which bacterial biofilms were grown for 7 days and by comparing these images with the ones obtained with X‐ray microtomography. NT images showed that the biofilm formed preferentially around the beads and at bead/bead interface. Visual comparison of both imaging techniques showed consistent biofilm spatial distributions and that the contrasting agent did not significantly disrupt the biofilm. NT images, on the other hand, were still too noisy to allow quantitative measurements. Therefore, X‐ray microtomography (provided it uses non‐disruptive contrast agents) seems to provide more reliable microstructural descriptors.
Human vocal folds possess outstanding abilities to endure large, reversible deformations and to vibrate up to more than thousand cycles per second. This unique performance mainly results from their ...complex specific 3D and multiscale structure, which is very difficult to investigate experimentally and still presents challenges using either confocal microscopy, MRI or X-ray microtomography in absorption mode. To circumvent these difficulties, we used high-resolution synchrotron X-ray microtomography with phase retrieval and report the first ex vivo 3D images of human vocal-fold tissues at multiple scales. Various relevant descriptors of structure were extracted from the images: geometry of vocal folds at rest or in a stretched phonatory-like position, shape and size of their layered fibrous architectures, orientation, shape and size of the muscle fibres as well as the set of collagen and elastin fibre bundles constituting these layers. The developed methodology opens a promising insight into voice biomechanics, which will allow further assessment of the micromechanics of the vocal folds and their vibratory properties. This will then provide valuable guidelines for the design of new mimetic biomaterials for the next generation of artificial larynges.
A 3D tri-phasic numerical model was developed to predict water vapor permeability in composite materials made of polypropylene (PP) as matrix and cellulose particles as fillers, with existence of an ...interphase around permeable inclusions. About 70 tri-phasic structures composed of ellipsoidal, heterogenous-size particles were generated to represent composites with four different filler contents (φp=2.96−6.06−12.67−19.91%v/v) with interfacial region at the filler/matrix interface (either 1 or 2 μm thick) displaying its own permeability. The relative permeability (i.e., ratio between composite and neat matrix permeability) was calculated from Finite Element Method (FEM) simulations on these structures. A good prediction of experimental relative permeability for the whole filler content range investigated was observed. The presence of a percolating interphase observed in some structures explains the high permeabilization observed for high φp. The proposed 3D numerical model was confronted to five state-of-the art analytical models and was the only one able to describe the observed complex structures with identification of reliable characteristics for the interphase (thickness, permeability).
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•Composite permeability exponentially increases with particle volume fraction due to percolation phenomena.•Algebraic equations could not be used alone without previously deep understanding of the composite morphology when percolation occurs.•FEM simulations well depicted permeability increases due to percolating interphase.•FEM simulations are needed for a better characterization of the interphase (thickness and diffusivity).
Snow stands out from materials at the Earth’s surface owing to its unique optical properties. Snow optical properties are sensitive to the snow microstructure, triggering potent climate feedbacks. ...The impacts of snow microstructure on its optical properties such as reflectance are, to date, only partially understood.
However, precise modelling of snow reflectance, particularly bidirectional reflectance, are required in many problems, e.g. to correctly process satellite data over snow-covered areas.
This study presents a dataset that combines bidirectional reflectance measurements over 500–2500 nm and the X-ray tomography of the snow microstructure for three snow samples of two different morphological types. The dataset is used to evaluate the stereological approach from Malinka (2014) that relates snow optical properties to the chord length distribution in the snow microstructure. The mean chord length and specific surface area (SSA) retrieved with this approach from the albedo spectrum and those measured by the X-ray tomography are in excellent agreement. The analysis of the 3D images has shown that the random chords of the ice phase obey the gamma distribution with the shape parameter m taking the value approximately equal to or a little greater than 2. For weak and intermediate absorption (high and medium albedo), the simulated bidirectional reflectances reproduce the measured ones accurately but tend to slightly overestimate the anisotropy of the radiation. For such absorptions the use of the exponential law for the ice chord length distribution instead of the one measured with the X-ray tomography does not affect the simulated reflectance. In contrast, under high absorption (albedo of a few percent), snow microstructure and especially facet orientation at the surface play a significant role in the reflectance, particularly at oblique viewing and incidence.
The mechanical efficiency of the biocementation process is directly related to the microstructural properties of the biocemented sand, such as the volume fraction of calcite, its distribution within ...the pore space (localized at the contact between grains, over the grain surfaces) and the contact properties: coordination number, contact surface area, contacts orientation and types of contact. In the present work, all these micromechanical properties are computed, for the first time, from 3D images obtained by X-ray tomography of intact biocemented sand samples. The evolution of all these properties with respect to the volume fraction of calcite is analyzed and compared between each other (from untreated sand to highly cemented sand). Whatever the volume fraction of calcite, it is shown that the precipitation of the calcite is localized at the contacts between grains. These results are confirmed by comparing our numerical results with analytical estimates assuming that the granular medium is made of periodic simple cubic arrangements of grains and by considering two extreme cases of precipitation: (1) The calcite is localized at the contact, and (2) the grains are covered by a uniform layer of calcite. In overall, the obtained results show that a small percentage of calcite is sufficient to get a large amount of cohesive contacts.
Permeability of textile fabrics with spherical inclusions Caglar, Baris; Orgéas, Laurent; Rolland du Roscoat, Sabine ...
Composites. Part A, Applied science and manufacturing,
August 2017, 2017-08-00, 2017-08, Letnik:
99
Journal Article
Recenzirano
We investigated the effect of rigid spherical inclusions such as microcapsules and fillers on the permeability of fabrics by using glass beads as model inclusions. Beads with a range of diameters ...(40–800μm) and volume fractions (2.5–10%) were sieved between layers of woven E-glass fabric targeting a fiber volume fraction of 40%. Permeability measurements were completed by X-ray microtomography to analyze the samples pore structure and estimate their permeability using Computational Fluid Dynamics simulations. Experimental and numerical estimates were also fitted with a Kozeny model accounting for porosity and specific surface of samples. We identified a threshold curve related to bead diameter and volume fraction below which the permeability follows that of a plain packed textile, and above which a strong departure from this trend is observed, induced by strong distortions of the textile. This behavior was closely correlated to the internal features of the textile.
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