Incremental response of granular materials: DEM results

We systematically investigate the incremental response of various equilibrium states of dense 2D model granular materials, along the biaxial compression path (\sigma 11 < \sigma 22, \sigma 12 = 0). Stress increments are applied in arbitrary directions in 3- dimensional stress space (\sigma 11, \sigma 22, \sigma 12). In states with stable contact networks we compute the stiffness matrix and the elastic moduli, and separate elastic and irreversible strains in the range in which the latter are homogeneous functions of degree one of stress increments. Without principal stress axis rotation, the response abides by elastoplasticity with a Mohr-Coulomb criterion and a non-associated flow rule. However a nonelastic shear strain is also observed for increments of \sigma 12, and shear and in-plane responses couple. This behavior correlates to the distribution of friction mobilization and sliding at contacts.Comment: 4 page

Incremental response of a model granular material by stress probing with DEM simulations

International audienceWe use DEM simulations on a simple 2D model of a granular material to test for the applicability of elastoplasticity (yield criterion, flow rule) to the response to stress increments of arbitrary directions. We apply stress probles in a three-dimensional stress space to various intermediate states (investigation points) along the biaxial compression path, and pay special attention to the influence of the magnitude of the increments The elastic part of the material response is systematically identified by building the elastic stiffness matrix of well-equilibrated configurations. The influences of the contact stiffness level and of the dominant strain mechanism, contact deformation (I) or network rearrangement (II), are considered. Stress increments sharing the same principal directions as the stress state in the ubvestigation point comply with a standard (single-mechanism) elastoplastic model with a Mohr-Coulomb criterion and well-defined flow rules and plastic moduli. Stress increments with principal axis rotation entail a response which is satifactorily modeled by superimposing 3 plastic mechanisms, 2 of them symmetrically corresponding to shear stresses of both signs. The full dependence of strain increments on sterss increments is thus parametrized with three flow rules, two of which are essentially symmetric

Numerical stress probing on a 2D model granular material

We use DEM simulations on a simple 2D model of a granular material to measure its deformation response to small stress increments of arbitrary directions (stress probes) and assess the applicability of the classical concepts of elastoplasticity. We impose stress increments in the space of principal stresses components, to numerical specimens selected at various intermediate states along the biaxial compression path. The elastic part of the incremental response is systematically identified by building the elastic stiffness matrix of well-equilibrated configurations. Plastic strain increments are computed standing on the partition hypothesis for strain increments into elastic- and plastic parts. The domain of validity of the partition hypothesis is discussed, playing extensively with the magnitude of the stress increments, in order to identify a range in which the incremental response is homogeneous of degree 1 and the essential features of plasticity models can be observed. We investigate in particular the existence of a plastic flow rule with a clearly defined plastic flow direction and yield criterion. The robustness of these features is tested over a range of contact stiffness levels and against the dominant deformation modes (i.e., based on contact deformation or network rearrangement)

A numerical experiment of backward erosion piping: kinematics and micromechanics

International audienceWe report on a numerical experiment by which we investigated the propagation of an erosion pipe in a water saturated granular soil. The simulation was performed with a two-dimensional implementation of the coupling between the discrete element method and the lattice Boltzmann method. A synopsis of the numerical scheme is provided. The specimen and testing conditions were designed as representative of the pipe front region. The kinematics of mobilisa-tion and fluidisation of the granular mass were investigated based on the physically-motivated definition of particle velocity thresholds. We measured a constant mass erosion rate, up to a clogging event. The study includes a micromechanical analysis of the response of the granular skeleton. We emphasise the influence of the unloading-induced damage on the erosion path, and the relevance of force chain arching as a self-organised resistance mechanism

Modélisation du comportement mécanique des grands CFRD (Identification des caractéristiques des enrochements et comportement du masque d'étanchéité amont)

Une modélisation numérique des grands barrages en enrochement à masque amont (CFRD) a été entreprise pour mieux comprendre les pathologies observées sur ces ouvrages récemment construits, principalement des fissures horizontales et verticales sur le masque amont en béton en phase de construction et de mise en eau. Le but de cette modélisation est ensuite de confirmer, préciser ou compléter les solutions proposées par les experts pour éviter ces désordres.D abord, une loi de comportement développée au sein d EDF-CIH appelée L&K-Enroch a été présentée. Il s'agit d'un modèle élastoplastique qui prend en compte les déformations irréversibles de l enrochement sous sollicitation déviatorique et isotrope dans les grands CFRD. Cette thèse propose aussi une méthode de calage des paramètres de ce modèle.Deux modélisations des barrages sont également présentées dans cette thèse afin de vérifier la fiabilité de la loi de comportement L&K-Enroch et de mieux comprendre les pathologies sur le masque amont en béton du CFRD. La modélisation en déformation plane (2D) est d abord entreprise et a comme support le barrage d Aguamilpa (180,5 m), au Mexique. Une modélisation plus poussée en 3D prenant en compte de l'effet de la vallée est ensuite entreprise. Elle a comme support le barrage de Mohale (145 m) au Lesotho.L'effet d échelle de l'enrochement est également étudié en comparant les résultats de simulation pour les matériaux de différentes tailles. L'impact de l effet d échelle sur le comportement du barrage est aussi analysé.Les simulations présentées en 2D et 3D sont une contribution à l'analyse du comportement mécanique des grands CFRD. Les résultats de la modélisation 2D montrent généralement une bonne correspondance avec les mesures in-situ. La modélisation 3D explique, d'une manière plus convaincante, l apparition des fissures sur le masque amont en béton des CFRD. Certaines mesures constructives sont finalement proposées afin de limiter ou d'éviter ces désordres dans le masque.A numerical modeling of high concrete face rockfill dam (CFRD) has been considered in order to better understand the pathology of cracks observed in the recently constructed high CFRD, especially the horizontal and vertical cracks detected on the concrete face slab during the construction and the impoundment. The purpose of this modeling is then to confirm, clarify or complete the solutions proposed by the experts to avoid these disorders.This PhD thesis presents a constitutive model developed by EDF-CIH known as L&K-Enroch. It is an elastoplastic model that takes into account the irreversible deformations of rockfill under deviatoric and isotropic loading in high CFRD. A first attempt of proposing a parameter calibration approach has been made as well.Two dam modellings are also presented in this thesis in order to verify the reliability of the constitutive model and to better understand the pathology of cracks observed on the concrete face slab of CFRD. A 2D modeling is compared to the behaviour of the 180.5 m Aguamilpa Dam, Mexico; a 3D modeling taking into account the valley effect is compared to the behaviour of the 145 m Mohale Dam, Lesotho.This thesis also studies the scale effect of rockfill through a comparison of the simulation results of materials of different sizes. The impact of the scale effect on the dam behavior is analyzed as well.The presented 2D and 3D simulations are a contribution to the analysis of the mechanical behaviour of high CFRD. The results of the 2D modeling show a relatively good agreement with the monitored data. The 3D modeling explains, in a rather convincing way, the pathology of cracks on the slab face of CFRD. Some measures are proposed to limit or avoid these different kinds of cracks.LYON-Ecole Centrale (690812301) / SudocSudocFranceF

Oleuropein-Laded Ufasomes Improve the Nutraceutical Efficacy

Ufasomes are unsaturated fatty acid liposomes made up of oleic and linoleic acids, natural components required in various biological processes. This kind of nanocarrier is characterized by a simple and dynamic structure and is able to improve the bioavailability of unsaturated fatty acids. The aim of this investigation was to evaluate ufasomes as natural compound delivery systems to deliver oleuropein and improve its antioxidant activity. Oleuropein is a phenolic compound mainly present in olives and olive oil, with several biological properties, such as the antioxidant activity. However, to improve their biological activity, antioxidant compounds should be able to cross cell membranes and uniformly incorporate in cells. Because of the great similarity between their constituents and cell membranes, ufasomes could be advantageous carriers for oleuropein delivery. The physico-chemical characteristics of ufasomes were investigated. A regular shape was shown by transmission electron microscopy studies, while the mean sizes were dependent on the ufasomes composition. In vitro studies highlighted that empty ufasomes did not lead to cell mortality at the tested concentrations and a good carrier internalization in CaCo-2 cells, further studies in vitro studies demonstrated that oleuropein-loaded ufasomes were able to enhance the antioxidant activity of the free active substance making this carrier a suitable one for nutraceutical application

Modélisation des renards hydrauliques : vers une approche discrète couplée

Une approche numérique discrète est présentée dans cette contribution afin de modéliser le front régressif d'érosion dans le phénomène de « renard hydraulique» pour les barrages et digues en terre. Les méthodes numériques discrètes DEM et LBM sont utilisées pour reproduire respectivement le comportement du squelette granulaire et du fluide interstitiel dans la région du front d'érosion

Sulforaphane-loaded ultradeformable vesicles as a potential natural nanomedicine for the treatment of skin cancer diseases

Sulforaphane is a multi-action drug and its anticancer activity is the reason for the continuous growth of attention being paid to this drug. Sulforaphane shows an in vitro antiproliferative activity against melanoma and other skin cancer diseases. Unfortunately, this natural compound cannot be applied in free form on the skin due to its poor percutaneous permeation determined by its physico-chemical characteristics. The aim of this investigation was to evaluate ethosomes® and transfersomes® as ultradeformable vesicular carriers for the percutaneous delivery of sulforaphane to be used for the treatment of skin cancer diseases. The physico-chemical features of the ultradeformable vesicles were evaluated. Namely, ethosomes® and transfersomes® had mean sizes &lt;400 nm and a polydispersity index close to 0. The stability studies demonstrated that the most suitable ultradeformable vesicles to be used as topical carriers of sulforaphane were ethosomes® made up of ethanol 40% (w/v) and phospholipon 90G 2% (w/v). In particular, in vitro studies of percutaneous permeation through human stratum corneum and epidermis membranes showed an increase of the percutaneous permeation of sulforaphane. The antiproliferative activity of sulforaphane-loaded ethosomes® was tested on SK-MEL 28 and improved anticancer activity was observed in comparison with the free drug

Neem oil or almond oil nanoemulsions for vitamin E Delivery: from structural evaluation to in vivo assessment of antioxidant and anti-inflammatory activity

Purpose: Vitamin E (VitE) may be classified in "the first line of defense" against the formation of reactive oxygen species. Its inclusion in nanoemulsions (NEs) is a promising alternative to increase its bioavailability. The aim of this study was to compare O/W NEs including VitE based on Almond or Neem oil, showing themselves antioxidant properties. The potential synergy of the antioxidant activities of oils and vitamin E, co-formulated in NEs, was explored. Patients and methods: NEs have been prepared by sonication and deeply characterized evaluating size, ζ-potential, morphology (TEM and SAXS analyses), oil nanodroplet feature, and stability. Antioxidant activity has been evaluated in vitro, in non-tumorigenic HaCaT keratinocytes, and in vivo through fluorescence analysis of C. elegans transgenic strain. Moreover, on healthy human volunteers, skin tolerability and anti-inflammatory activity were evaluated by measuring the reduction of the skin erythema induced by the application of a skin chemical irritant (methyl-nicotinate). Results: Results confirm that Vitamin E can be formulated in highly stable NEs showing good antioxidant activity on keratinocyte and on C. elegans. Interestingly, only Neem oil NEs showed some anti-inflammatory activity on healthy volunteers. Conclusion: From the obtained results, Neem over Almond oil is a more appropriate candidate for further studies on this application

Numerical photogrammetry in laboratory experiences on 2D slopes

In this preliminary study a numerical photogrammetry system was tested in measuring incremental displacement fields in slope models realised with analogous Schneebeli material. Two tests were performed corresponding to different sets of boundary conditions on the displacements; controlled and uncontrolled deformation scenery were experienced. The resulting measures showed efficiency, limits and perspective of this measuring technique