Porous materials

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Wetting and drying of porous materials

Wetting and drying of porous materials

When dry porous materials (having wetable surfaces) come in contact with liquid water, the wetting process that follows involves capillary conduction, where suction acts as the driving force, and is quite different from water vapour diffusion. Wetting by liquid water proceeds as a front involving a very steep gradient of moisture content. The advance of this front into the porous material is characteristic of the material (each material having its rate constant) and decreases with the square of the distance travelled. It will take approximately four times as long to pass through a sample 2 inches thick as it will a sample 1 inch thick, both of identical material. When the wetting front passes through the material, thus saturating it, the flow ceases unless a head or pressure difference is applied on the source of water. The flow that follows through the saturated material involves a different process, being controlled by the permeability and the hydraulic pressure difference. Wetting by contact with liquid water produces very large moisture content gradients, in contrast with wetting by vapour unless the latter also involves a temperature gradient.
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Optical porosimetry of weakly absorbing porous materials

Optical porosimetry of weakly absorbing porous materials

and l s 0 , respectively, of a ceramic material (n = 1.75) and of 12 granulated pharmaceutical tablets (n = 1.5) with various porosities. Two sets of tablets were manufactured from the compression of two sieve fractions (150 µm granules sizes for group A and 150-400 µm for group B). The physical porosity of these porous materials was measured using mercury intrusion and the optical porosity was computed after Eq. (7). For the ceramic material, the measured physical porosity was 0.34 and the measured optical porosity was 0.149. Application of Eq. (9) (assuming a random mixture because µ a was negligible) gives an optical porosity of 0.144, very close to the
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2016 — Computational design of functionally graded hip implants by means of additively manufactured porous materials

2016 — Computational design of functionally graded hip implants by means of additively manufactured porous materials

Article published in the journal « Computer Methods in Biomechanics and Biomedical Engineering, Taylor & Francis », 2015, 19(8): 845-854 3.1 Abstract The mechanical properties of well-ordered porous materials are related to their geometrical parameters at the mesoscale. Finite element analysis (FEA) is a powerful tool to design well- ordered porous materials by analysing the mechanical behaviour. However, FE models are often computationally expensive. This article aims to develop a cost-effective FE model to simulate well-ordered porous metallic materials for orthopaedic applications. Solid and beam FE modelling approaches are compared, using finite size and infinite media models considering cubic unit cell geometry. The model is then applied to compare two unit cell geometries: cubic and diamond. Models having finite size provide similar results than the infinite media model approach for large sample sizes. In addition, these finite size models also capture the influence of the boundary conditions on the mechanical response for small sample sizes. The beam FE modelling approach showed little computational cost and similar results to the solid FE modelling approach. Diamond unit cell geometry appeared to be more suitable for orthopaedic applications than the cubic unit cell geometry.
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Prediction of forming limits for porous materials using void-size dependent model and bifurcation approach

Prediction of forming limits for porous materials using void-size dependent model and bifurcation approach

Abstract The scientific literature has shown the strong effect of void size on material response. Several yield functions have been developed to incorporate the void size effects in ductile porous materials. Based on the interface stresses of the membrane around a spherical void, a Gurson- type yield function, which includes void size effects, is coupled with the bifurcation theory for the prediction of plastic strain localization. The constitutive equations as well as the bifurcation- based localization criterion are implemented into the finite element code ABAQUS/Standard within the framework of large plastic deformations. The resulting numerical tool is applied to the prediction of forming limit diagrams (FLDs) for an aluminum material. The effect of void size on the prediction of FLDs is investigated. It is shown that smaller void sizes lead to an increase in the ductility limits of the material. This effect on the FLDs becomes more significant for high initial porosity, due to the increase of void-matrix interface strength within the material.
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Failure of elasto-plastic porous materials due to void shape effects and void growth

Failure of elasto-plastic porous materials due to void shape effects and void growth

Abstract : This work makes use of the recently proposed second-order nonlinear homogenization model (SOM) for (visco)plastic porous materials to study the influence of the Lode parameter and the stress triaxiality on the failure of metallic materials. This model is based on the “second-order” or “generalized secant” homogenization method and is capable of handling general “ellipsoidal” void shapes (i.e., particulate microstructures with more general orthotropic overall anisotropy) and general three-dimensional loa- ding conditions.

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Cyclic behavior of elasto-plastic porous materials subjected to triaxial loading conditions

Cyclic behavior of elasto-plastic porous materials subjected to triaxial loading conditions

Mots clés — Elasto-plasticity, Porous materials, Cyclic loading, Homogenization. 1 Introduction Although significant advances have been made these last years in ductile fracture and monotonic loading conditions, a lot of questions remain open in the domain of cyclic response of materials. In particular, large amount of experimental data [1, 2] has shown a strong dependence of the material cyclic response upon the applied pressure. In this regard, consideration of a porous-matrix material system allows for a physical interpretation of pressure-dependent cyclic responses. More precisely, non linear homogenization models [3, 4] and micromechanical models [5] for elasto-plastic porous materials have been used for the prediction of material softening mainly due to the porosity evolution under monotonic loading conditions. To achieve that, a precise prediction of the evolution of the microstructure is needed (e.g., evolution of volume, shape and orientation of voids). On the other hand, many numerical and analytical results have been obtained concerning the influence of stress triaxiality [6, 7], denoted here as X Σ , and defined as the ratio between the mean stress to the von Mises equivalent or effective deviatoric stress. Recently, the effects of the third stress invariant, through the Lode angle [8, 9] in monotonic loading states have also been investigated. Nevertheless, much less has been studied in the context of cyclic loading conditions [10, 11] with a main emphasis on axisymmetric loading states. Even if in the majority of studies in the bibliography, cyclic response is analyzed using small strain calculations considering macroscopic strain amplitudes in the range of 1% − 5%, local strains can be in excess of 100% due to strong localization of the deformation around impurities or voids as is the present case. For that reason, it is critical that a finite deformation analysis is carried out. In this regard, the scope of this study is to investigate the effect of cyclic loading conditions and finite deformations upon microstructure evolution and material softening/hardening using FEM periodic unit-cell calculations with 3D geometry.
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Failure of elasto-plastic porous materials subjected to triaxial loading conditions

Failure of elasto-plastic porous materials subjected to triaxial loading conditions

model (SOM) for (visco)plastic porous materials [1] to study the influence of the Lode parameter and the stress triaxiality on the failure of metallic materials. This model is based on the “second-order” or “generalized secant” homogenization method [2] and is capable of handling general “ellipsoidal” microstructures (i.e., particulate microstructures with more general orthotropic overall anisotropy) and general three-dimensional loading conditions.

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Divalent heavy metals adsorption on various porous materials: removal efficiency and application

Divalent heavy metals adsorption on various porous materials: removal efficiency and application

158 The work done in this thesis is dedicated to heavy metals removal from wastewater. This can be accomplished by several methods including adsorption on porous materials. Adsorption is considered an inexpensive and efficient method for removing heavy metals even at low concentrations. Several adsorbents with different physical and chemical properties have been studied. However, comparing the adsorption performance of these materials is difficult because the experimental conditions vary from one study to another. Among the various materials studied in literature, a great deal of attention is paid nowadays to organically modified mesoporous silicates and nanocasted mesoporous carbons. In this study the goal was to immobilize EDTA, which has good divalent cations chelating properties, on different types of mesostructured silica (SBA-15, SBA-16 and KIT-6). Then their efficiencies in removing Cu 2+ , Ni 2+ , Cd 2+ and Pb 2+ from aqueous solutions were compared with that of mesoporous carbon CMK-3 and Faujasite zeolite type X that served as the reference material.
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Effect of temperature distribution on moisture flow in porous materials

Effect of temperature distribution on moisture flow in porous materials

Effect of temperature distribution on moisture flow in porous materials Woodside, W.; Kuzmak, J. M. https://publications-cnrc.canada.ca/fra/droits L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB.

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Coalescence criteria for porous materials with small-scale voids

Coalescence criteria for porous materials with small-scale voids

Some examples of porous materials with small-scale voids From the Nuclear Industry: Irradiated materials (Ding et al., 2016) (CEA - DMN/SEMI/LM2E Microscopy team) Nanovoids are observed to contribute to the fracture of the material through classical mechanisms of ductile fracture:

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Random Auxetic Porous Materials from Parametric Growth Processes

Random Auxetic Porous Materials from Parametric Growth Processes

Abstract We introduce a computational approach to optimize random porous materials through parametric growth processes. We focus on the problem of minimizing the Poisson’s ratio of a two-phase porous random material, which results in an auxetic material. Initially, we perform a parametric optimization of the growth process. Afterward, the optimized parametric growth process implicitly generates an auxetic random material. Namely, the growth process intrinsically entails the formation of an auxetic material. Our approach enables the computation of large-scale auxetic random materials in commodity computers. We also provide numerical results indicating that the computed auxetic materials have close to isotropic linear elastic behavior.
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Experimental Demonstration of Entrance/Exit Effects on the Permeability Measurements of Porous Materials

Experimental Demonstration of Entrance/Exit Effects on the Permeability Measurements of Porous Materials

Hazen-Darcy equation is only applicable when the velocity of the fluid is sufficiently small so that that the Reynolds number of the flow is around unity or smaller. [3] Davis and Olague have shown from their analysis of the experimental datasets published by Darcy that for velocities higher than 4 × 10 –3 m/s, the normalized pressure drop vs fluid velocity is better represented by quadratic model than by a linear one. [4] As the velocity increases, the influences of inertia and turbulence become more significant and the results diverge from the linear Darcy model. This departure eventually causes the pressure-drop across a porous medium to be gov- erned by inertial effects, which depends on the fluid density q and quadratic velocity V 2 . The physical phenomenon respon- sible for the quadratic term in Equation 3 is assumed to be the force imposed to the fluid by solid surface obstructing the fluid flow path. According to Newton, this resistivity is pro- portional to the fluid density and the average fluid velocity square. [5] The addition of this contribution gives the Hazen- Dupuit-Darcy equation:
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Resistance of porous materials to rain

Resistance of porous materials to rain

Without waterproofing these 20 cm, thick walls were traversed with difficulty by the rain (more than 8 hours artificial rain) but they took a very long time to dry (more than one m[r]

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Impregnation as a technique for measuring zero porosity modulus of porous materials

Impregnation as a technique for measuring zero porosity modulus of porous materials

It might have been expected that the compaction technique would produce residual strains in the material and that a modulus of elasticity versus porosity relation different than that f[r]

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Pressures developed during the unidirectional freezing of water-saturated porous materials

Pressures developed during the unidirectional freezing of water-saturated porous materials

Heaving pressure measurenlents with unsorted glass beads show t h e significance of the smaller beads in producing the ultimate ice lens pressures.. 1, \vhich hacl[r]

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In-Pore stress by drying-induced capillary bridges inside porous materials.

In-Pore stress by drying-induced capillary bridges inside porous materials.

NaCl primary crystal and pore membrane wall, before the secondary precipitation. (d)[r]

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Accurate 3D microstructure characterisation of porous materials by X-ray microtomography

Accurate 3D microstructure characterisation of porous materials by X-ray microtomography

Hervé Delingette, Modélisation, déformation et reconnaissance d'objets tridimensionnels à l'aide de maillages simplexes, PhD thesis, Ecole centrale de Paris, 1994.. Active surface[r]

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Study of new porous materials for silicon microfabricated column development in gas chromatography

Study of new porous materials for silicon microfabricated column development in gas chromatography

Another approach for the synthesis of monodispersed mesostructured nanoparticles consisted in the growth of silica shell around a template, the latter being eventually further removed to generate hollow core shell particles. “Soft” templates such as surfactant vesicles, 27 bacteria, 28 or gas bubble 29 were used, however they often led to ill-defined shapes and polydispersed particles with a disordered porous arrangement and unpredictable pore sizes. At the reverse, the use of “hard” templates such as polymer latex and surfactants as co- template afforded a more reliable approach for the synthesis of structured silica particles. 30-31 A recent work, from H. Blas et al. 32 reported the synthesis of individual monodispersed spherical hollow mesostructured silica nanoparticles, with calibrated and oriented pores (perpendicular orientation with respect to the core surface). Such structures could be of great interest for chromatographic applications as it offers to control independently several structural parameters such as the particle diameter and the shell thickness.
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A possible force mechanism associated with the freezing of water in porous materials

A possible force mechanism associated with the freezing of water in porous materials

L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB. Highway Rese[r]

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Suction and its use as a measure of moisture contents and potentials in porous materials

Suction and its use as a measure of moisture contents and potentials in porous materials

NRC Publications Record / Notice d'Archives des publications de CNRC: https://nrc-publications.canada.ca/eng/view/object/?id=3737e2f5-06be-4ccf-b6bc-af323d024f29 https://publications-cnr[r]

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