Yves Rémond - Profile on Academia.edu (original) (raw)

Papers by Yves Rémond

Life, Feb 3, 2022

A cell-mechanobiological model is used for the prediction of bone density variation in rat tibiae... more A cell-mechanobiological model is used for the prediction of bone density variation in rat tibiae under medium and high mechanical loads. The proposed theoretical-numerical model has only four parameters that need to be identified experimentally. It was used on three groups of male Wistar rats under sedentary, moderate intermittent and continuous running scenarios over an eight week period. The theoretical numerical model was able to predict an increase in bone density under intermittent running (medium intensity mechanical load) and a decrease of bone density under continuous running (higher intensity mechanical load). The numerical predictions were well correlated with the experimental observations of cortical bone thickness variations, and the experimental results of cell activity enabled us to validate the numerical results predictions. The proposed model shows a good capacity to predict bone density variation through medium and high mechanical loads. The mechanobiological balance between osteoblast and osteoclast activity seems to be validated and a foreseen prediction of bone density is made available.

Multiscale bone remodeling : dream or reality ?

HAL (Le Centre pour la Communication Scientifique Directe), Nov 1, 2022

Prediction of osteoporotic degradation of tibia human bone at trabecular scale

Journal of The Mechanical Behavior of Biomedical Materials, Mar 1, 2023

HAL (Le Centre pour la Communication Scientifique Directe), Apr 22, 2020

On cherche à tester la capacité d'un modèle macroscopique simplifié à simuler l'évolution de l'ép... more On cherche à tester la capacité d'un modèle macroscopique simplifié à simuler l'évolution de l'épidémie de Covid-19 au niveau d'un pays ou d'une entité géographique, pour peu que l'évolution des conditions de son développement soient suffisamment homogènes sur le territoire considéré. On pense par exemple à des dates de confinement uniformes sur ce territoire, ou à une gestion globale suffisamment uniforme également. Par modélisation, on entend la capacité de simuler chaque jour ou de façon cumulée, l'évolution des nombres de cas détectés, les hospitalisations simples ou en réanimation, et le cas échéant les décès ou guérisons. La modélisation proposée ici se fonde sur les équations classiques des épidémies [1], mais tient compte des effets d'un confinement au niveau macroscopique. Seuls les détections de malades infectés par le Covid-19 sont présentées ici. La modélisation proposée permet cependant une application facile aux autres indicateurs de l'épidémie. Elle est identifiée par des paramètres qui possèdent une signification épidémiologique simple, ce qui permet de comparer les évolutions de l'épidémie entre trois pays : France, Italie et Espagne. L'optimisation des paramètres est effectuée par un processus classique de machine learning. Le modèle est applicable à tout pays dont les caractéristiques de gestion de l'épidémie sont similaires. Covid-19, épidémie, modélisation, simulation, machine learning, Cas infectés On trouvera facilement de très nombreuses publications récentes ou plus anciennes proposant des modélisations sophistiquées des épidémies. Les avancées dans ce domaine sont importantes et suivent les nouvelles capacités de simulation numérique, de modélisation mathématique comme d'optimisation par des techniques d'intelligence artificielle. Ces modèles profitent également de l'amélioration continue de la qualité des données. Il est impossible de citer tous ces travaux et ce n'est d'ailleurs pas l'objet de cet article. On pourra cependant consulter les travaux de T.L. Wiemken et R.R. Kelley [2], ou de V. Colizza & al. [3]. Parmi les plus récents, on pourra également consulter les travaux de Lin Jia et al. [4] ou de D. Caccavo . L'objectif de cette étude est de répondre à la question de savoir dans quelle mesure une modélisation macroscopique simplifiée couplée à une identification automatique par machine learning donne des résultats intéressants qui peuvent être appliqués à l'épidémie du Covid-19 de début 2020. Les prévisions de son développement en fonction des politiques

HAL (Le Centre pour la Communication Scientifique Directe), 2020

IOS Press eBooks, May 18, 2021

Almost all cells in the human body are subjected to mechanical stresses. These forces can vary fr... more Almost all cells in the human body are subjected to mechanical stresses. These forces can vary from a few Pascals (shear stress) to some mega Pascals (on hip cartilage). It is now well known that mechanical forces have a decisive effect on cellular physiology. In 1880, W. Roux introduced the concept of functional adaptation; which can be defined as a quantitative autoregulation controlled by stimuli like mechanical forces. These stresses influence functionality and cellular metabolism and can lead to appropriate tissue remodelling by triggering a cascade of reactions (mechanotransduction), being the signal for the adaptation of cells and tissues. However, although the main biological effects of mechanical forces are well documented, the relation between mechanical forces and physiological phenomena is largely unknown. In this paper, some effects of mechanical stresses on different cells (mesenchymal stem cells, bone cells, chondrocyte, endothelial cells, vascular or muscular cells, etc.) are summarized.

Blood flow numerical simulation in a realistic liver model : effect of blood pressure on the liver rigidity

A new cellulo-mechanobiological model for the prediction of bone degradation under high mechanical load

Could the Application of a Compaction Force Impact the Outcome of Alveolar Bone Grafting?

Facial plastic surgery & aesthetic medicine, Dec 31, 2020

Computer Methods in Biomechanics and Biomedical Engineering, Oct 19, 2020

Journal of Cellular Immunotherapy, Sep 1, 2018

Bio-medical Materials and Engineering, Mar 30, 2017

In this work, we present an evolutive trabecular model for bone remodeling based on a boundary de... more In this work, we present an evolutive trabecular model for bone remodeling based on a boundary detection algorithm accounting for both biology and applied mechanical forces, known to be an important factor in bone evolution. A finite element (FE) numerical model using the Abaqus/Standard ® software was used with a UMAT subroutine to solve the governing coupled mechanical-biological non-linear differential equations of the bone evolution model. The simulations present cell activation on a simplified trabeculae configuration organization with trabecular thickness of 200 µm. For this activation process, the results confirm that the trabeculae are mainly oriented in the active direction of the principal mechanical stresses and according to the principal applied mechanical load directions. The trabeculae surface activation is clearly identified and can provide understanding of the different bone cell activations in more complex geometries and load conditions.

Doklady Physics, Mar 1, 2017

The features of a Newtonian-fluid flow in a two-dimensional channel with sudden contraction and e... more The features of a Newtonian-fluid flow in a two-dimensional channel with sudden contraction and expansion are investigated by numerical modeling. The kinetics of the bifurcation transition from the symmetric mode to steady-state asymmetric flow on the outlet from the zone of contraction of the channel is analyzed. The linear dependence of the degree of asymmetry of flow on the Reynolds number is established.

Mathematics and mechanics of complex systems, Sep 2, 2020

We are trying to test the capacity of a simplified macroscopic virus-centric model to simulate th... more We are trying to test the capacity of a simplified macroscopic virus-centric model to simulate the evolution of the SARS CoV 2 epidemic (COVID 19) at the level of a country or a geographical entity, provided that the evolution of the conditions of its development (behaviors, containment policies) are sufficiently homogeneous on the considered territory. For example, a uniformly deployed lockdown on the territory, or a sufficiently uniform overall crisis management. The virus-centric approach means that we favor to model the population dynamic of the virus rather than the evolution of the human cases. In other words, we model the interactions between the virus and its environment -for instance a specific human population with a specific behavior on a territory, instead of modeling the interactions between individuals. Therefore, our approach assumes that an epidemic can be analyzed as the combination of several elementary epidemics which represent a different part of the population with different behaviors through time. The modeling proposed here is based on the finite superposition of Verhulst equations commonly known as logistic functions and used in dynamics of population. Modelling the lockdown effect at the macroscopic level is therefore possible. Our model has parameters with a clear epidemiological interpretation, therefore the evolution of the epidemic can be discussed and compared among four countries: Belgium, France, Italy, and Spain. Parameter optimization is carried out by a classical machine learning process. We present the number of infected patients with SARS-CoV-2 and a comparison between data from the European Centre for Disease Prevention and Control and the modeling. In a general formulation, the model is applicable to any country with similar epidemic management characteristics. These results show that a simple two epidemics decomposition is sufficient to simulate with accuracy the effect of a lockdown on the evolution of the COVID-19 cases.

Shape memory polymers: constitutive modeling, calibration, and simulation

Elsevier eBooks, 2023

A detailed review on constitutive models for thermoresponsive shape memory polymers

Elsevier eBooks, 2023

Equilibrium and transient swelling of soft and tough pH-sensitive hydrogels: constitutive modeling and FEM implementation

Elsevier eBooks, 2023

Life, Feb 3, 2022

Multiscale bone remodeling : dream or reality ?

HAL (Le Centre pour la Communication Scientifique Directe), Nov 1, 2022

Prediction of osteoporotic degradation of tibia human bone at trabecular scale

Journal of The Mechanical Behavior of Biomedical Materials, Mar 1, 2023

HAL (Le Centre pour la Communication Scientifique Directe), Apr 22, 2020

HAL (Le Centre pour la Communication Scientifique Directe), 2020

IOS Press eBooks, May 18, 2021

Blood flow numerical simulation in a realistic liver model : effect of blood pressure on the liver rigidity

A new cellulo-mechanobiological model for the prediction of bone degradation under high mechanical load

Could the Application of a Compaction Force Impact the Outcome of Alveolar Bone Grafting?

Facial plastic surgery & aesthetic medicine, Dec 31, 2020

Computer Methods in Biomechanics and Biomedical Engineering, Oct 19, 2020

Journal of Cellular Immunotherapy, Sep 1, 2018

Bio-medical Materials and Engineering, Mar 30, 2017

Doklady Physics, Mar 1, 2017

Mathematics and mechanics of complex systems, Sep 2, 2020

Shape memory polymers: constitutive modeling, calibration, and simulation

Elsevier eBooks, 2023

A detailed review on constitutive models for thermoresponsive shape memory polymers

Elsevier eBooks, 2023

Equilibrium and transient swelling of soft and tough pH-sensitive hydrogels: constitutive modeling and FEM implementation

Elsevier eBooks, 2023

Polymer Science Series A, Jan 1, 2008

The stress-strain behavior of HDPE under uniaxial tensile drawing below the yield point is discus... more The stress-strain behavior of HDPE under uniaxial tensile drawing below the yield point is discussed. Special attention is placed on studying the tensile loading-unloading diagrams at different unloading rates. Experimental data are analyzed in terms of a set of two-phase basic structural mechanical elements, which take into account the plastic flow and structural rearrangements of both hard and soft components. Parameters of these elements are calculated by optimal fitting of theoretical curves to an arbitrary experimental tensile loading-unloading curve measured at a constant strain rate. This approach allows description of a decrease in the residual strain with decreasing unloading rate at fixed model parameters. The physical nature of the observed deformational effects is considered.

Journal of Materials Science, Jan 1, 2012

The review focuses on the current studies of the deformation response and accompanying structural... more The review focuses on the current studies of the deformation response and accompanying structural transformations of thermoplastic semicrystalline polymers subjected to uniaxial tension prior to the yield point. The mechanisms of strain-induced cavitation of amorphous layers and damages of crystalline lamellae are analyzed in line with novel results on the deformation behavior of solid polymers at temperatures exceeding the glass transition point. The coupling of viscoelastic and plastic deformation mechanisms with the small-strain structural transformations is critically discussed on the basis of the advanced theoretical modeling of mechanical properties of semicrystalline polymers.

univ-ubs.fr

RESUME : Les pièces en polymère semi-crisallins obtenues par injection sont de plus en plus utili... more RESUME : Les pièces en polymère semi-crisallins obtenues par injection sont de plus en plus utilisées comme pièces de structure. Il est alors nécessaire de connaître les caractéristiques mécaniques le plus précisément possible. Cependant, la connaissance et la prédiction des caractéristiques mécaniques sont encore loin d'être maîtrisés, même si les processus physiques sont connus. L'étude présentée se restreint à la détermination expérimentale par un montage de vibrations libres de la variation du module d'Young dans l'épaisseur des pièces injectées. Le procédé d'injection, qui conduit aussi à des zones cristallines d'architecture variable, influence les propriétés mécaniques des polymères semi-cristallins. L'influence du temps de refroidissement et de la température du moule, et donc du taux de cristallinité, est mesuré sur la répartition des modules E i dans l'épaisseur de pièces thermoplastiques semicristallines. Les résultats présentés concernent le polyamide 6-6.

Journal of Engineering …, Jan 1, 2011

By the 2000=53=CE directive, the European Union leads to develop the recycling process industry, ... more By the 2000=53=CE directive, the European Union leads to develop the recycling process industry, specially the plastic one, for end of life vehicles (ELV). To value these recycled materials by an isofunction use, as for example for car semistructure elements, it is necessary for the mechanical properties to be better known. In this study, the effects of the recycling process on the mechanical behavior of polypropylene (PP)=elastomeric, talc particles filled or not, are presented, through different loading tests: tensile (small and finite strain), bending and creep tests. The failure, plasticity, and elasticity parameters modifications are established. Tensile and bending tests lead to some similar characteristics evolution as, for example elastic modulus values. The creep behavior evolution is more complex to understand. Both materials have a near finite strain macroscopic behavior so that, taking account of each component (talc, EPDM or EPR elastomeric part) the intrinsic behavior can be well described in the mechanical model finally presented.

Polymer Degradation …, Jan 1, 2012

The impact of recycling by grinding and re-extrusion on the physical and mechanical properties of... more The impact of recycling by grinding and re-extrusion on the physical and mechanical properties of polypropylene (PP)/ethylene octene copolymer (EOC) blends was investigated. The considered EOC content was 0 wt. %, 10 wt. % and 20 wt. %, and the investigated number of recycling passes (extrusions) was 0, 1, 3 and 6. Up to 6 re-extrusions, an increase of the melt flow index (MFI), a slight increase of the crystallinity, a slight decrease of the decomposition temperature (T onset ), and no significant oxidation were noted. Therefore, the recycling of the blends induces thermomechanical degradation by chain scission without oxidation. Increasing the content of EOC increases the MFI and the T onset of the PP blends. The first recycling procedure induced an increase of the Young's modulus and tensile yield stress, while for higher recycling numbers, these two parameters dropped. The EOC inclusions stabilized the tensile elongation at break up to 3 recycling procedures due to a decrease of their size and a homogenization of their shape, while that of neat PP continuously decreased with recycling numbers.

The interphase layer in semicrystalline polyethylene (PE) serves as the transition between the cr... more The interphase layer in semicrystalline polyethylene (PE) serves as the transition between the crystalline lamellae and the amorphous domains and is recognized as the third constituent of PE. When PE undergoes large deformations, this interphase layer together with the amorphous phase behaves hyperelastically. Because of the metastable nature and nanometric size of the interphase and its intimate mechanical coupling to the neighboring crystal and amorphous domains, detailed characterization of its hyperelastic properties have eluded detailed experimental evaluation. To extract these properties, a combined algorithm is proposed based on applying the constitutive relations of an isotropic, compressible, hyperelastic continuum to the molecular dynamics simulation results of a PE stack from (Lee and Rutledge, 2011). The simulation element is incrementally deformed to a large strain, during which the stress--strain information is recorded. Assuming a neo--Hookean model, the tensorial constitutive equation is derived. The hyperelastic parameters for the central amorphous phase, the interphase layer, and the interlamellar domain are identified with the help of the optimization notion and a set of positive objective functions. The identified hyperelastic parameters for the interlamellar domain are in good agreement with the ones estimated experimentally and frequently used in the literature for the noncrystalline phase. The specifically developed sensitivity analysis indicates that the shear modulus is identified with a higher degree of certainty, in contrast to the bulk modulus. It is also revealed that the presented continuum mechanics analysis is able to capture the melting/recrystallization and rotation of crystalline chains that take place during the deformation. The evolutions of the boundaries of the hyperelastic elements are also identified concurrently with the hyperelastic parameters as the by--product of the presented methodology. Fig 1 A) Schematic illustration of a PE stack and the relative positioning of the constituents. The arrows indicate the direction of the applied displacement constraints in the MD simulations. B) Edited schematic of the simulated PE stack in its unloaded state together with the average density distribution along the stack (Reprinted with permission from ref. 11 .

Semi-crystalline polyethylene is composed of three domains: crystalline lamellae, the compliant a... more Semi-crystalline polyethylene is composed of three domains: crystalline lamellae, the compliant amorphous phase, and the so-called "interphase" layer separating them. Among these three constituents, little is known about the mechanical properties of the interphase layer. This lack of knowledge is chiefly due to its mechanical instability as well as its nanometric thickness impeding any property measuring experiments. In this study, the Monte Carlo molecular simulation results for the interlamellar domain (i.e. amorphous+ interphases), reported in (in ) are employed. The amorphous elastic properties are adopted from the literature and then two distinct micromechanical homogenization approaches are utilized to dissociate the interphase stiffness from that of the interlamellar region. The results of the two approaches match perfectly, which validates the implemented dissociation methodology. Moreover, a hybrid numerical technique is proposed for one of the approaches when the recursive method poses numerical divergence problems. Interestingly, it is found that the dissociated interphase stiffness lacks the common feature of positive definiteness, which is attributed to its nature as a transitional domain between two coexisting phases. The sensitivity analyses carried out reveal that this property is insensitive to the non-orthotropic components of the interlamellar stiffness as well as the uncertainties existing in the interlamellar and amorphous stiffnesses. Finally, using the dissociated interphase stiffness, its effective Young's modulus is calculated. The evaluated Young's modulus compares well with the effective interlamellar Young's modulus for highly crystalline polyethylene, reported in an experimental study. This satisfactory agreement along with the identical results produced by the two micromechanical approaches confirms the validity of the new information about the interphase elastic properties in addition to making the proposed dissociation methodology quite reliable to be applied to similar problems.

Polymer, Jan 1, 2005

The mechanical response of solid amorphous polymers is strongly dependent on the temperature and ... more The mechanical response of solid amorphous polymers is strongly dependent on the temperature and strain rate. More specifically, the yield stress increases dramatically for the low temperatures as well as for the high strain rates. To describe this behavior, we propose a new formulation of the cooperative model of Fotheringham and Cherry where the final mathematical form of the model is derived according to the strain rate/temperature superposition principle of the yield stress. According to our development, the yield behavior can be correlated to the secondary relaxation and we propose an extension of the model to temperatures above the glass transition temperature. For a wide range of temperatures and strain rates (including the impact strain rates), the predicted compressive yield stresses obtained for the polycarbonate (PC) and the polymethylmethacrylate (PMMA) are in excellent agreement with the experimental data found in the literature.

Modeling of strain rates and temperature effects on the yield behavior of amorphous polymers

Journal De Physique Iv, Jan 1, 2003

Three molecular theories are used to predict the yield behavior of amorphous polymers for a wide ... more Three molecular theories are used to predict the yield behavior of amorphous polymers for a wide range of temperatures and strain rates. These include the state transition theory of Ree-Eyring, the conformational change theory of Robertson and the disclinations theory of Argon. For each of these models, the yield stress behavior of polymethylmethacrylate (PMMA) is described over a wide range

Polymer Testing, Jan 1, 2004

The polymer processing conditions used in injection moulding strongly influence mechanical proper... more The polymer processing conditions used in injection moulding strongly influence mechanical properties of materials in the solid state. This investigation presents an experimental method for measuring the local Young’s modulus and its application to polyoxymethylene (POM), polyamide 66 and glass fibre-filled polyamide 66 test pieces. An inverse method allowing local longitudinal Young’s moduli to be estimated from local natural flexural frequencies has been evaluated. The results obtained reveal a large variation in the local Young’s modulus over the thickness of an injection moulded piece, in particular in the outer skin zone. The influence of the various operational parameters has been evaluated.

Mechanical behavior of composite based polypropylene: Recycling and strain rate effects

Journal De Physique Iv, Jan 1, 2006

Journal of Materials Science, Jan 1, 2004

The small strain (below yielding) tensile loading-unloading tests were carried out on the low-den... more The small strain (below yielding) tensile loading-unloading tests were carried out on the low-density polyethylene (LDPE) and polypropylene (PP) at low strain rate and room temperature. The experiments unambiguously indicate to a remarkable decrease in residual strains in comparison with those predicted by conventional viscoelastic models. These deviations cannot be explained without taking into account structural transformations of semi-crystalline polymers. As long as small deformations cannot result in significant change in content and texture of crystalline and amorphous components, it was assumed that such transformations should include disintegration of connectivity in crystallite clusters. This structural rearrangement is supposed to be caused by the strain-induced decrystallization of narrow (and thus highly stressed) “bridges” connecting domains of conjugated crystallites or inside crystallites. A simple 1D modelling of the deformation processes supports this expectation. The disconnection in polymer morphology is simulated by small portions of amorphous ligaments appearing between neighbouring crystallites in the course of deformation. In spite of simplicity of the model a precise fitting of the stress-strain diagram is obtained along with small variations in structural and material characteristics (crystallinity degree, effective rigidity and plastic ability) of the concerned polymers.

Composites Science and Technology, Jan 1, 2005

The simulation, by traditional uni-dimensional rheological models, of viscoelastic unloading to z... more The simulation, by traditional uni-dimensional rheological models, of viscoelastic unloading to zero stress after tensile testing of short glass fiber-reinforced polyethylene and its pure matrix is poor. The models significantly underestimate recovery rates, even with small amounts of strain. The use of a finite number of relaxation times does not sufficiently increase recovery rates during unloading when models are generated from the responses of materials under load. Similar results and observations are obtained using rate jumps in loading and unloading. 3D models developed using local state methods require that an additional recovery potential should be used. This observation seems to prove that it is necessary to take into account the evolution of the polyethylene microstructure while the stress is applying, thus justifying the existence of the additional potential. The similar situation that exists for pure polyethylene means that the phenomenon must not be confused with material damage.

Polymer, Jan 1, 2005

In many applications, polymer materials undergo a large variety of mechanical loading conditions,... more In many applications, polymer materials undergo a large variety of mechanical loading conditions, wherein the influences of temperature and strain rate are of prime importance. Mahieux and Reifsnider [Mahieux CA, Reifsnider KL. Polymer 2001;42:3281. [19]] have proposed a statistical model to describe the stiffness variation of polymers over a wide range of temperatures. However, this model does not consider any frequency/strain rate dependence of the stiffness modulus. Starting from this consideration, we propose here to transform this latter model into a robust physically based model for the prediction of the stiffness modulus for a wide range of temperatures and frequencies/strain rates. This new formulation has been successfully validated for two amorphous polymers, polymethylmethacrylate (PMMA) and polycarbonate (PC), using dynamic mechanical analysis and uniaxial compression testing. Good agreement has been found between theory and experiment for the non-linear behavior of the initial Young's modulus, at the very high strain rates.

Polymer Science Series A, Jan 1, 2006

A general approach to the description of the mechanical properties of materials whose deformation... more A general approach to the description of the mechanical properties of materials whose deformation is accompanied by considerable structural rearrangements is developed. As in the case of classical simulation of the deformation behavior of viscoelastic and elastoplastic bodies, the concept of basic structural-mechanical element that reflects the properties of a fragment of a continuous medium is introduced. The simplest version of two alternative structural states is considered. Equations that define the kinetics of transition between these states and the mechanical properties of the base structural-mechanical element include expressions for elastic strain, plastic flow, and structure evolution. It is assumed that structural transitions and plastic flow are effected by the thermofluctuation mechanism. It is shown that the array of elements characterized by an appropriate set of parameters can describe the specific features of deformation behavior and structure evolution for a wide range of materials, in particular, polymers and composites, at their early deformation stages.

Polymer Science Series A, Jan 1, 2008

Modélisation des non-linéarités en vitesse de déformation et du comportement en déchargement des ... more Modélisation des non-linéarités en vitesse de déformation et du comportement en déchargement des polymères semi-cristallins -Les lois viscoélastiques classiques ne permettent pas de décrire complètement les comportements caractéristiques des polymères semi-cristallins, comme ceux observés lors de sauts de vitesses ou en déchargement. Nous présentons dans cet article certaines particularités du comportement mécanique pour un polyéthylène ou un polypropylène en petites déformations. Un modèle physique incluant une évolution de la microstructure est présenté et comparé aux observations expérimentales. Ce modèle permet une forte amélioration des simulations des comportements mécaniques en chargement et déchargement pour une large classe de polymères semicristallins.

Journal of Engineering Materials and …, Jan 1, 2011

The peculiarities of viscoelastic behavior of high-density polyethylene (HDPE) subjected to the u... more The peculiarities of viscoelastic behavior of high-density polyethylene (HDPE) subjected to the uniaxial cyclic tensions and retractions below the yield point are studied. This required using three different deformation programs including (i) the successive increase in strain maximum of each cycle, (ii) the controlled upper and lower stress boundaries, and (iii) the fixed strain at the backtracking points. The experimental data are analyzed in a framework of the modified structure-sensitive model , "Principles of Structural-Mechanical Modeling of Polymers and Composites," Polym. Sci. Ser. A, 48, pp. 1004-1013) of semicrystalline polymers. It is supposed that increase in the interlamellar nanovoid volume fraction results in speeding-up the plastic flow rate while decreasing cavitation rate. Consequently, a proper fitting of the stress-strain cyclic diagrams is obtained for the applied deformation programs within the common set of model parameters. This makes it possible to reveal evolution of nanovoid volume fraction in HDPE during cyclic deformations.

Third International Conference on Polymer Behavior

Applied …, Jan 1, 2009

Modélisation du Comportement du PE et du PP basée sur la Théorie de VBO: Effet de la vitesse de déformation

Depos 20 Du 8 au 10 mars 2006 Obernai, Jan 1, 2004

Comptes Rendus Mécanique, Jun 6, 2012

Second gradient continuum mixture model Hierarchically heterogeneous materials Micro-structure-re... more Second gradient continuum mixture model Hierarchically heterogeneous materials Micro-structure-related size effects Natural bone tissue Bio-resorbable material Bone resorption and synthesis Load-induced replacement of artificial material with natural bone tissue Numerical simulations

Surgical and Radiologic …, Jan 1, 2012

In this paper, we investigated the brain-sinus junction and especially the bridging veins linking... more In this paper, we investigated the brain-sinus junction and especially the bridging veins linking these two organs. Two types of optical microscopy were used: conventional optical microscopy and digital microscopy. We used thin histological sections prepared from a human brain, and stained with Masson's trichrome, hemalun and orcein. Finally we observed the path of the bridging vein inside the brain-skull interface. At smaller scales, wavy collagen fiber bundles were found and characterized inside the vein walls. Taking into account the orientations of the different sections with reference to frontal planes, we found that the bridging vein has a very complex geometry, which increases the difficulty to determine fiber orientations in its walls. Nevertheless, we found that collagen fiber bundles are mainly circumferentially oriented in the superior sagittal sinus walls. In this paper, we were able to characterize precisely the path of the bridging vein from the brain to the sinus, with different magnifications.

Effects of homogenization technique and introduction of interfaces in a multiscale approach to predict the elastic properties of arthropod cuticle

Journal of the mechanical behavior of biomedical materials, 2013

Effective elastic properties of arthropod endocuticle using a multiscale approach.Step by step ho... more Effective elastic properties of arthropod endocuticle using a multiscale approach.Step by step homogenization technique.Effects of homogenization technique.Effect of interfaces (interphases) at different scales of the microstructure.In this paper the mechanical response of the arthropod cuticle is evaluated by means of a multiscale approach including interface effects. The cuticle's elastic behavior is modeled at the nano and the micro scales by mean-field homogenization techniques. With respect to the work of Nikolov et al. (2011), the idea has been extended to study, at different scales of the structure, the effect of the used homogenization technique as well as the interface effect on the global elastic properties. First results revealed the sensitivity of the used homogenization technique on the global predicted elastic properties of the arthropod cuticle. To account for the interface between the fillers and the matrix of the composite structure of the arthropod cuticle, interphases are assumed at different scales of the structure with the same shape and topological orientation as the fillers. The approaches are based on few parameters directly related to the mechanical properties, the volume fraction and the morphology of the interphase. Results of the predicted elastic properties using the multiscale model including interphases are in good agreement with the experimental results. We show that the introduction of interphases leads to an improvement of the global elastic response in comparison to the multiscale model without interphases.

Journal of the mechanical behavior of biomedical materials, 2013

The purpose of the present work is to propose a new multiscale model for the prediction of the me... more The purpose of the present work is to propose a new multiscale model for the prediction of the mechanical behavior of vein walls. This model is based on one of our previous works which considered scale transitions applied to undulated collagen fibers. In the present work, the scale below was added to take the anisotropy of collagen fibrils into account. One scale above was also added, modeling the global reorientation of collagen fibers inside the vessel wall. The model was verified on experimental data from the literature, leading to a satisfactory agreement. The proposed multiscale approach also allows the extraction of local stresses and strains at each scale. This approach is presented here in the case of vein walls, but can easily be extended to other tissues which contain similar constituents.

Computer Methods and Programs in Biomedicine, Jan 1, 2010

c o m p u t e r m e t h o d s a n d p r o g r a m s i n b i o m e d i c i n e 1 0 0 ( 2 0 1 0 ) 1... more c o m p u t e r m e t h o d s a n d p r o g r a m s i n b i o m e d i c i n e 1 0 0 ( 2 0 1 0 ) 149-157 Kidney Mechanical behaviour Bulk modulus Free breathing Real time a b s t r a c t This article presents a method of predictive simulation, patient-dependant, in real time of the abdominal organ positions during free breathing. The method, that considers both influence of the abdominal breathing and thoracic breathing, needs a tracking of the patient skin and a model of the patient-specific modification of the diaphragm shape. From a measurement of the abdomen viscera kinematic during free breathing, we evaluate through a finite element analysis, the stress field sustained by the organs for a hyperelastic mechanical behaviour using large strain theory. From this analysis, we deduce an in vivo Poisson's ratio and a homogeneous bulk modulus of the liver and kidneys, and compare it to the ones in vitro available in the literature.

Computer methods in biomechanics and biomedical engineering, 2013

Journal of Mechanics of …, Jan 1, 2012

Bridging veins (BVs) are frequently damaged in traumatic brain injury due to brain-skull relative... more Bridging veins (BVs) are frequently damaged in traumatic brain injury due to brain-skull relative motion. These veins, connected to the superior sagittal sinus (SSS), are prone to rupture upon head impact giving rise to an acute subdural hematoma (ASDH). We modeled the biomechanical characteristics of ASDH to study the behavior of the SSS-BVs compound with its surrounding medium. The almost periodic distribution of the BVs along the SSS allowed the use of the homogenization method based on asymptotic expansion to calculate the effective elastic properties of the brain-skull interface region. The representative volume element (RVE) under study is an anisotropic equivalent medium with homogenized elastic properties, accounting for the variations of each constituent's mechanical properties. It includes the sinus, the BVs and blood, and the surrounding cerebrospinal fluid and tissue. The results show large variations in the RVE anisotropic properties depending on each constituent of the BV and, to a certain extent, on the variability of the surrounding constituents' mechanical properties.

In this paper we present a new method to predict in real time from a preoperative CT image the in... more In this paper we present a new method to predict in real time from a preoperative CT image the internal organ motions of a patient induced by his breathing. This method only needs the segmentation of the bones, viscera and lungs in the preoperative image and a tracking of the patient skin motion. Prediction of internal organ motions is very important for radiotherapy since it can allow to reduce the healthy tissue irradiation. Moreover, guiding system for punctures in interventional radiology would reduce significantly their guidance inaccuracy. In a first part, we analyse physically the breathing motion and show that it is possible to predict internal organ motions from the abdominal skin position. Then, we propose an original method to compute from the skin position a deformation field to the internal organs that takes mechanical properties of the breathing into account. Finally, we show on human data that our simulation model can provide a prediction of several organ positions (liver, kidneys, lungs) at 14 Hz with an accuracy within 7 mm.

Prediction of abdominal organ positions during free breathing is a major challenge from which sev... more Prediction of abdominal organ positions during free breathing is a major challenge from which several medical applications could benefit. For instance, in radiotherapy it would reduce the healthy tissue irradiation. In this paper, we present a method to predict in real-time the abdominal organs position during free breathing. This method needs an abdo-thoracic preoperative CT image, a second one limited to the diaphragm zone, and a tracking of the patient skin motion. It also needs the segmentation of the skin, the viscera volume and the diaphragm in both preoperative images. First, a physical analysis of the breathing motion shows it is possible to predict abdominal organs position from the skin position and a modeling of the diaphragm motion. Then, we present our original method to compute a deformation field that considers the abdominal and thoracic breathing influence. Finally, we show on two human data that our simulation model can predict several organs position at 50 Hz with accuracy within 2-3 mm.

Progress in Biophysics & Molecular Biology, Jan 1, 2010

Prediction of abdominal viscera and tumour positions during free breathing is a major challenge f... more Prediction of abdominal viscera and tumour positions during free breathing is a major challenge from which several medical applications could benefit. For instance, in radiotherapy it would reduce the healthy tissue irradiation. In this paper, we present a new approach to predict real-time abdominal viscera positions during free breathing. Our method needs an abdo-thoracic 3D preoperative CT or MR image, a second one limited to the diaphragmatic area, and a tracking of the patient’s skin position. First, a physical analysis of the breathing motion shows it is possible to predict accurately abdominal viscera positions from the skin position and a modelling of the diaphragm motion. Secondly, a quantitative analysis of the skin and organ motion allows us to define the demands our real-time simulation has to fulfill. Then, we present in detail all the necessary steps of our original method to compute a deformation field from data extracted in both 3D preoperative image and skin surface tracking. Finally, experiments carried out with two human data show that our simulation model predicts abdominal viscera positions, such as liver, kidneys or spleen, at 50 Hz with an accuracy within 2–3 mm.

Bridging veins are frequently damaged in traumatic brain injury. These veins are prone to rupture... more Bridging veins are frequently damaged in traumatic brain injury. These veins are prone to rupture in their subdural portion upon head impact, due to brain-skull relative motion, giving rise to an acute subdural hematoma. To understand the biomechanical characteristics of this hematoma, we take into account the periodical distribution of bridging veins in the sagittal plane. This allowed the use of the method of homogenization by asymptotic expansion to calculate the homogenized elastic properties of the brain-skull interface region. The geometry of this zone was simplified and a representative volume element was developed comprising: sinus, bridging vein, blood circulating inside them, surrounding cerebrospinal fluid and tissues. The heterogeneous elementary cell is transformed to an anisotropic homogenous equivalent medium and the homogenized elastic properties were calculated. The macroscopic homogenized properties resulted from the current study can be incorporated into a finite element model of the human head at macroscopic scale. The main results of this homogenization theory are the calculation of the local stress field into the elementary cell, as well as its homogeneous anisotropic properties at the macroscopic scale.

Fast Segmentation of Abdominal Wall: Application to Sliding Effect Removal for Non-rigid Registration

… and Clinical Applications, Jan 1, 2012

Composites Science and Technology, Jan 1, 2010

Effective conductivity of polymer composites, filled with conducting fibers such as carbon nanotu... more Effective conductivity of polymer composites, filled with conducting fibers such as carbon nanotubes, is studied using statistical continuum theory. The fiber orientation distribution in the matrix plays a very important role on their effective properties. To take into account their orientation, shape and distribution, two-point and three-point probability distribution functions are used. The effect of fibers orientation is illustrated by comparing the effective conductivity of microstructures with oriented and non-oriented fibers. The randomly oriented fibers result in an isotropic effective conductivity. The increased fiber orientation distribution can lead to higher anisotropy in conductivity. The effect of fiber’s aspect ratio on the effective conductivity is studied by comparing microstructures with varying degrees of fiber orientation distribution. Results show that the increase in anisotropy leads to higher conductivity in the maximum fiber orientation distribution direction and lower conductivity in the transverse direction. These results are in agreement with various models from the literature that show the increase of the aspect ratio of fibers improves the electrical and thermal conductivity.

Composite Structures, Jan 1, 1987

This paper deals with tridirectional composite material mechanical behaviour. The different const... more This paper deals with tridirectional composite material mechanical behaviour. The different constituents of the composite material are fibre-yarns, matrix and their respective interfaces. The mechanical behaviours of these constituents are built up for each of them. They are characterised by some parameters from the elastic domain, up to the rupture. These parameters are identified by using classical and original tests on a tridirectional carbon-carbon composite.Micro-macro mechanical relationships are then given. They derive from simple physical ideas and are founded on damage notion and homogenisation theory.This approach completes another mechanical model of the homogeneous behaviour for this material.Comparisons between the theoretical and experimental results are given.

Cette étude porte sur la caractérisation des dommages de plaques stratifiées carbone/époxy suite ... more Cette étude porte sur la caractérisation des dommages de plaques stratifiées carbone/époxy suite à un impact basse vitesse. Les stratifiés étudiés sont constitués de nappes pré-imprégnées unidirectionnelles superposées de M21/T700GC. Les essais ont été réalisés en faisant varier masse de l'impacteur et hauteur de chute en conservant pour chaque essai, un niveau d'énergie identique recommandée par la norme aéronautique. L'instrumentation de l'essai ainsi que l'analyse multi physique réalisée sur les plaques impactées ont permis de mieux comprendre les mécanismes d'endommagements du matériau stratifié testé. En effet, ont été couplés accéléromètre, caméra rapide et jauges de déformations pour les mesures pendant l'essai. Une étude thermographique et une analyse aux ultrasons des plaques impactées ont révélés la localisation des endommagements dans les différents stratifiés testés. A niveau d'énergie initiale constante, les plaques testées avec la masse la plus importante sont très largement endommagées par rapport aux plaques impactées avec une faible masse.

Un essai de compression-flexion pour la caractérisation de matériaux à deux phases : Application à l’endommagement surfacique de carbone-carbone

Existence d'un endommagement de subsurface sur des composites carbone-carbone après frottement intense

Comptes Rendus De L Academie Des Sciences Serie Ii Fascicule B-mecanique Physique Astronomie, Jan 1, 1998

On met en évidence un endommagement spécifique localisé au voisinage du bord d'une structure comp... more On met en évidence un endommagement spécifique localisé au voisinage du bord d'une structure composite, lorsque celle-ci a subi un frottement intense de type freinage. La mesure de cet endommagement est rendue délicate à la fois par la géométrie particulière de ces structures, mais aussi par l'hétérogénéité et la porosité habituelles des matériaux utilisés, les plus performants pour résister aux températures élevées. On identifie cet endommagement par meso-dureté et à des profondeurs successives dans le voisinage de la surface de contact.Evidence is presented of specific damage localized at the edge of carbon-carbon structures submitted to high tribological solicitations like braking. The measurement of this damage is more difficult on account of the geometry of braking structures, but also because of the heterogeneity and porosity typically displayed by the composites used, which are extremely resistant to high temperature. Evaluation of damage is based on meso-hardness at various depths under the braking surface.

This paper deals with the measurement of subsurface damage of composite materials after braking s... more This paper deals with the measurement of subsurface damage of composite materials after braking situations. Several carbon–carbon composites materials have been studied and tested under industrial braking conditions. Two damage measurement methods were used to estimate the braking effects on the mechanical behaviour of these materials. In particular, a meso-hardness test has been adapted to the heterogeneity of carbon–carbon composite and to their macro-porosity. Depending on the type of material, the results show that meso-hardness is a good indicator of local behaviour at a small depth under the surface. For one C–C composite, reinforced with long random fibers, we measure the evolution of damage as a function of the distance of the braking surface. Another original compression-bending test was also used, which confirms this damaged subsurface effect before wear occurs.

Etude du vieillissement de polymères thermoplastiques chargés de fibres de verre

CR JNC11, Arcachon, Jan 1, 1998

French national conference on composites JNC13

Composites science and technology, Jan 1, 2005

La chimie et le sport

... Auteurs : Alain Berthoz, Jean-François Caron, Marie-Florence Grenier-Loustalot, Charles-Yanni... more ... Auteurs : Alain Berthoz, Jean-François Caron, Marie-Florence Grenier-Loustalot, Charles-Yannick Guezennec, Pierre Letellier, Claude Lory, Denis Masseglia, Nicolas Puget, Isabelle Queval, YvesRémond, Fabien Roland, Jean-François Toussaint et Jean-Luc Veuthey. ...

The global mechanical behaviour of a 4D carbon–carbon (C– C 4D) composite material is described. ... more The global mechanical behaviour of a 4D carbon–carbon (C– C 4D) composite material is described. Designed for aeronautic applications and particularly for the brake discs of heavy air craft, this material is a layered composite reinforced in three directions in the plane (−60°, 0°, 60°) to which the fourth direction of reinforcement is perpendicular. Having ascertained the compliance matrices in the plane to which the braking surface is parallel, we have determined the engineering constants of an elementary ply from the basic assumptions of the classical laminations theory (CLT). Finally, to construct both linear-elastic and elastoplastic constitutive equations of the C– C 4D, we propose a thermodynamic model that accurately characterises the behaviour of this material. This simple model can be identified from simple mechanical tests.

Sur la reconstitution du comportement mécanique d'un matèriau composite 3 D à partir de ses constituants

Mechanism and Machine Theory, Jan 1, 2009

We propose hereafter a unified model of epicyclic gear trains, based on a primitive parametric ke... more We propose hereafter a unified model of epicyclic gear trains, based on a primitive parametric kernel, which contains all usual gear train formulations of any compound gear train. We show that the nested and the Ravigneaux gear train derive from a unified model, which permits to obtain the formulation of ratio and efficiency. Therefore the conception of a gear train if the kinematics or dynamics are fixed can be solved with an analytical resolution.

Journal of Materials Processing Technology, Jan 1, 2009

A transient three-dimensional finite element model is developed to simulate the phase transformat... more A transient three-dimensional finite element model is developed to simulate the phase transformation during the selective laser sintering process; taking into account the thermal and sintering phenomena involved in this process. A bi-level structure integration procedure is chosen, in which the temperature dependent thermal conductivity, specific heat, and density are integrated at the outer level then used as material constants for the integration of the heat equation in the inner level. Results for temperature and density distribution, using a polycarbonate powder, are presented and discussed.

Comptes Rendus de l'Academie des …, Jan 1, 1999

La description cinematique d'un systeme donne de solides rigides (resolution du probleme direct) ... more La description cinematique d'un systeme donne de solides rigides (resolution du probleme direct) ne permet pas d'aborder le probleme de son invention. Le problbme inverse, c'est-a-dire l'obtention du concept si la cinematique est fixee (entree-sortie) n'a jamais et6 aborde de facon analytique. On propose, a partir dune approche pararrktrique, une formulation permettant de resoudre le probleme inverse pour tout train epicycldidal a deux &ages. En outre, pour ces m6canismes, on met en evidence une tbeorie unifite dont le noyau primitif est une fonction hqmographique de tous les parametres du systeme. 0 1999 Academic des sciences/Editions scientifiques et medicales Elsevier SAS

Comptes Rendus De L Academie Des Sciences Serie Ii Fascicule B-mecanique Physique Astronomie, Jan 1, 1999

La description cinématique d'un système donné de solides rigides (résolution du problème direct) ... more La description cinématique d'un système donné de solides rigides (résolution du problème direct) ne permet pas d'aborder le problème de son invention. Le problème inverse, c'est-à-dire l'obtention du concept si la cinématique est fixée (entrée-sortie) n'a jamais été abordé de façon analytique. On propose, à partir d'une approche paramétrique, une formulation permettant de résoudre le problème inverse pour tout train épicycloïdal à deux étages. En outre, pour ces mécanismes, on met en évidence une théorie unifiée dont le noyau primitif est une fonction homographique de tous les paramètres du système.The calculation of a given gear train (solution of the direct problem) is never really difficult, but does not give one any idea how it was invented. Since the inverse problem (i.e. obtaining the concept if the kinematics are fixed) has never been approached in an analytical way, we propose, from the general formula of the ratios, a single equation which enables one to resolve the inverse problem for every two-level gear train, and suggest new unified kinematic and dynamic formulations.

Materials Science Forum, Jan 1, 2007

In the selective laser sintering (SLS) manufacturing technique a pre-heated layer of material pow... more In the selective laser sintering (SLS) manufacturing technique a pre-heated layer of material powder undergoes a laser radiation in a selective way to produce three dimensional metallic or polymeric solid parts. Here, we consider sintering of polymer powder. The phase transformation in this process involves the material heat transfer which is strongly affected by the material sintering phenomena. A transient three dimensional finite element model is developed to simulate the phase transformation during the selective laser sintering process. This model takes into account the heat transfer in the material (powder and solid), the sintering and the transient nature of this process. The numerical simulation of the set of equations, describing the problem, is made possible by means of the commercial finite element software Abaqus. A bi-level structure integration procedure is chosen, in which the density is integrated at the outer level and the heat equation is integrated in the inner level. After successfully computing the integration of the density, a material Jacobian representing the thermal phenomena is computed and supplemented the Abaqus Code via an implicit user subroutine material. Results for temperature and density distribution, using a polycarbonate powder, are presented and discussed.

A new approach to solving the inverse problem for compound gear trains

Journal of Mechanical Design, Jan 1, 1999

ABSTRACT

Bulletin-Institut de l'engrenage et des …, Jan 1, 1997

Une méthode générale de résolution du problème inverse pour les systèmes de trains épicycloïdaux

Bulletin-Institut de l'engrenage et des …, Jan 1, 1996

Computational Materials …, Jan 1, 2012

The mechanical response of few-layer graphene (FLG), consisting of 2-7 atomic planes and bulk gra... more The mechanical response of few-layer graphene (FLG), consisting of 2-7 atomic planes and bulk graphite is investigated by means of molecular dynamics simulations. By performing uniaxial tension tests at room temperature, the effects of number of atomic planes and chirality angle on the stress-strain response and deformation behavior of FLG were studied using the Tersoff potential. It was observed that by increasing of the FLG number of layers, the increase of bonding strength between neighboring layers reduce the elastic modulus and ultimate strength. It was found that, while the chirality angle of FLG showed a significant effect on the elastic modulus and ultimate tensile strength of two and three graphene layers, it turns to be less significant when the numbers of layers are more than four. Finally, by plotting the deformation behavior, it was concluded that FLGs present brittle performance.

Physics Letters A, Jan 1, 2012

In this Letter, we used classical Molecular Dynamics (MD) simulations to investigate the tensile ... more In this Letter, we used classical Molecular Dynamics (MD) simulations to investigate the tensile behavior of graphene. The validity of the proposed MD architecture is verified by comparing the simulation results with the available experimental results. By performing uniaxial tension simulations, we studied the effects of strain rate, chirality, nanoribbons width and number of atomic planes on the mechanical properties of graphene. We particularly investigated the effects of doped nitrogen atoms and point vacancies concentrations on the Young's modulus and tensile strength of graphene. By plotting the deformation process of graphene at various strain levels, the failure behavior is discussed.

Solid State …, Jan 1, 2011

In this study, the effects of nitrogen atom substitution and curvature on the thermal conductivit... more In this study, the effects of nitrogen atom substitution and curvature on the thermal conductivity of graphene are studied using non-equilibrium molecular dynamics (NEMD) simulations. Using the optimized Tersoff potential proposed by Lindsay and Broido [L. Lindsay, D.A. Broido, Phys. Rev. B 82 (2010) 205441], the predicted thermal conductivity of graphene is close to the experimental range. It was observed that only 1% concentration of nitrogen doping in graphene decreases the thermal conductivity of graphene by more than 50% and removes its chirality dependency. Our simulations also show that graphene is a high flexible structure and suggest limited curvature effects on its thermal conductivity.

Qualitative Equivalence Between Electrical Percolation Threshold and Effective Thermal Conductivity in Polymer/Carbon Nanocomposites

Journal of Engineering …, Jan 1, 2012

... Majid Baniassadi, Akbar Ghazavizadeh, Yves R??mond, Said Ahzi, David Ruch, Hamid Garmestani. ... more ... Majid Baniassadi, Akbar Ghazavizadeh, Yves R??mond, Said Ahzi, David Ruch, Hamid Garmestani. ... Baniassadi, M., Addiego, F., Laachachi, A., Ahzi, S., Garmestani, H., Hassouna, F., Makradi, A., Toniazzo, V., and Ruch, D., 2011, ???Using SAXS Approach to Estimate Thermal ...

Application of the Strong Contrast Technique to Thermoelastic Characterization of Nanocomposites

Supplemental …

... Majid Baniassadi&#x27;&#x27;2, Akbar Ghazavizadeh3, David Ruch&#x27; ... more ... Majid Baniassadi&#x27;&#x27;2, Akbar Ghazavizadeh3, David Ruch&#x27; ,Yves Rémond2, Said Ahzi2, Hamid Garmestani4 &#x27;Centre de ... University of Aveiro, 3810-193, Aveiro, Portugal &quot;School of Materials Science and Engineering, Georgia Institute of Technology, 771 Ferst Dr. NW Atlanta ...

Atomistic-Continuum Modeling of the Mechanical Properties of Silica/Epoxy Nanocomposite

Journal of Engineering …, Jan 1, 2012

ABSTRACT In this study, a hierarchical multiscale homogenization procedure aimed at predicting th... more ABSTRACT In this study, a hierarchical multiscale homogenization procedure aimed at predicting the effective mechanical properties of silica/epoxy nanocomposites is presented. First, the mechanical properties of the amorphous silica nanoparticles are investigated by means of molecular dynamics (MD) simulations. At this stage, the MD modeling of three-axial tensile loading of amorphous silica is carried out to estimate the elastic properties. Second, the conventional twp phase homogenization techniques such as finite elements (FE), Mori-Tanaka (M-T), Voigt and Reuss methods are implemented to evaluate the overall mechanical properties of the silica/epoxy nanocomposite at different temperatures and at constant weight ratio of 5%. At this point, the mechanical properties of silica obtained in the first stage are used as the inputs of the reinforcing phase. Comparison of the FE and M-T results with the experimental results in a wide range of temperatures reveals fine agreement; however, the FE results are in better agreement with the experiments than those obtained by M-T approach. Additionally, the results predicted by FE and M-T methods are closer to the lower bound (Reuss), which is due to lowest surface to volume ratio of spherical particles. [DOI: 10.1115/1.4005419]

Mechanics of Materials, Jan 1, 2010

Continuum damage mechanics is used to model the damage induced by a thermal shock to the R7T 7 gl... more Continuum damage mechanics is used to model the damage induced by a thermal shock to the R7T 7 glass, the French borosilicate glass used for nuclear waste vitrification. A finite element model of the thermal shock is developed in which the elastic constitutive equations are coupled with an anisotropic stress-based damage evolution law. The Weibull distributions of strength measured at various temperatures by biaxial flexural tests are used to identify the parameters of this damage evolution law. Vibration tests are conducted to identify the elastic properties of the glass and to determine the effect of thermal shock-induced damage on the glass residual stiffness. The residual stiffness predicted by the damage model agrees with that measured experimentally. The fractured surface in the glass after a thermal shock is estimated, assuming that all the elastic energy associated with the stresses that are higher than a pre-determined threshold is dissipated in the creation of new surfaces. Comparison between the predicted and experimentally-measured fractured surface is performed. The model is shown to capture the saturation of the crack network density for severe thermal shocks; whereas this is not the case if damage is not accounted for in the constitutive equations.

Journal of Engineering …, Jan 1, 2012

For a better understanding of the thermomechanical behavior of glasses used for nuclear waste vit... more For a better understanding of the thermomechanical behavior of glasses used for nuclear waste vitrification, the cooling process of a bulk borosilicate glass is modeled using the finite element code Abaqus. During this process, the thermal gradients may have an impact on the solidification process. To evaluate this impact, the simulation was based on thermal experimental data from an inactive nuclear waste package. The thermal calculations were made within a parametric window using different boundary conditions to evaluate the variations of temperature distributions for each case. The temperature differences throughout the thickness of solidified glass were found to be significantly non-uniform throughout the package. The temperature evolution in the bulk glass was highly responsive to the external cooling rates applied; thus emphasizing the role of the thermal inertia for this bulky glass cast.

Journal of nanoscience and nanotechnology, 2010

In this paper, we report the use of the TMCVD technique for the optimisation of deposited diamond... more In this paper, we report the use of the TMCVD technique for the optimisation of deposited diamond films onto Ti6Al4V substrates. A number of samples were made varying the experimental parameters. The specimen surfaces were characterised using micro Raman spectra and SEM analyses. Results show that very different surface finish (from micro to nanostructures) and film characteristics can be obtained from the experimental parameters used. The quality of deposited diamond is very dependant on the experimental settings and process. It was found that lower residual stresses are developed using the TMCVD technique than with conventional CVD but depend on the structural diamond growth during the process. The quality of the deposited film was evaluated as a function of diamond to amorphous carbon ratio but showed no direct relation with the surface finish since it characterises the quality of the deposited diamond but not the quality of the film surface.

Thin Solid Films, Jan 1, 2010

In this paper, we present numerical simulations of the residual stresses developed between diamon... more In this paper, we present numerical simulations of the residual stresses developed between diamond coatings and Ti-6Al-4V substrates when using chemical vapour deposition technique. The large difference in thermal expansion coefficients of diamond and titanium alloys results in high residual stresses in the diamond film. This could lead to interfacial cracking and material failure. The finite element method was used to simulate the cooling process of diamond films at various thicknesses and deposited at temperatures ranging from 600 °C to 900 °C. The influence of different parameters such as temperature, film thickness, material characteristics, geometry and edge effects are investigated for different case geometries. The film debonding and cracking is discussed and numerical results are compared with existing experimental and numerical results. Finally, some propositions are made to enhance the experimental process in order to reduce the residual stress intensities and the possible material degradation.

Physica E: Low-dimensional Systems and …, Jan 1, 2012

c MD is used for studying the thermal and tensile response of boron-nitride sheets. c Elastic mod... more c MD is used for studying the thermal and tensile response of boron-nitride sheets. c Elastic modulus is acquired to be around 800-850 GPa and dependent on chirality. c Boron-nitride nanostructures present highly brittle failure behavior. c Thermal conductivity is predicted to be around 80 W/m-K and independent of chirality.

Despite the success of surgical implants such as artificial hip, materials used in these procedur... more Despite the success of surgical implants such as artificial hip, materials used in these procedures still do not satisfy the demands of human life time functioning. Currently used materials such as titanium alloys, ceramics and polymers are degraded after about a dozen years of use. Diamond coating technology has proven to be efficient in the performance of human joints. In this study, we have investigated the deposition of diamond thin films on Ti6Al4V using a new developed time-modulated Chemical Vapour Deposition (TMCVD) method. Finite element simulations were used to analyse the development of residual stresses. Micro Raman spectroscopy was also used to evaluate the residual stresses and compare with numerical models.

Materials & Design, Jan 1, 2010

In the present work a mesh free method is used to study the effect of interfaces on the crack pro... more In the present work a mesh free method is used to study the effect of interfaces on the crack propagation path in multilayered like Solid Oxide Fuel Cells (SOFCs) materials. The partition of unity principle was introduced to model the crack tip singularity. The penalty method is used to model the materials discontinuity along the interfaces. The stress intensity factors (SIF) were computed using the interaction integral. The mesh free method is implemented and verified using results from the literature. A parametric study of crack propagation in mono-layer and bi-layer material is conducted. Finally an application to SOFC unit shows that crack initiated in the anode propagates towards the anode/electrolyte interface.

Applied RVE Reconstruction and Homogenization of Heterogeneous Materials

Statistical correlation functions are a well-known class of statistical descriptors that can be u... more Statistical correlation functions are a well-known class of statistical descriptors that can be used to describe the morphology and the microstructure-properties relationship. A comprehensive study has been performed for the use of these correlation functions for the reconstruction and homogenization in nano-composite materials. Correlation functions are measured from different techniques such as microscopy (SEM or TEM), small angle X-ray scattering (SAXS) and can be generated through Monte Carlo simulations. In this book, different experimental techniques such as SAXS and image processing are presented, which are used to measure two-point correlation function correlation for multi-phase polymer composites.

Higher order correlation functions must be calculated or measured to increase the precision of the statistical continuum approach. To achieve this aim, a new approximation methodology is utilized to obtain N-point correlation functions for multiphase heterogeneous materials. The two-point functions measured by different techniques have been exploited to reconstruct the microstructure of heterogeneous media.

Statistical continuum theory is used to predict the effective thermal conductivity and elastic modulus of polymer composites. N-point probability functions as statistical descriptors of inclusions have been exploited to solve strong contrast homogenization for effective thermal conductivity and elastic modulus properties of heterogeneous materials. Finally, reconstructed microstructure is used to calculate effective properties and damage modeling of heterogeneous materials.

The Journal of chemical physics, 2014

An approximate solution for n-point correlation functions is developed in this study. In the appr... more An approximate solution for n-point correlation functions is developed in this study. In the approximate solution, weight functions are used to connect subsets of (n-1)-point correlation functions to estimate the full set of n-point correlation functions. In previous related studies, simple weight functions were introduced for the approximation of three and four-point correlation functions. In this work, the general framework of the weight functions is extended and derived to achieve optimum accuracy for approximate n-point correlation functions. Such approximation can be utilized to construct global n-point correlation functions for a system when there exist limited information about these functions in a subset of space. To verify its accuracy, the new formulation is used to approximate numerically three-point correlation functions from the set of two-point functions directly evaluated from a virtually generated isotropic heterogeneous microstructure representing a particulate composite system. Similarly, three-point functions are approximated for an anisotropic glass fiber/epoxy composite system and compared to their corresponding reference values calculated from an experimental dataset acquired by computational tomography. Results from both virtual and experimental studies confirm the accuracy of the new approximation. The new formulation can be utilized to attain a more accurate approximation to global n-point correlation functions for heterogeneous material systems with a hierarchy of length scales. © 2014 AIP Publishing LLC.

Journal of The Mechanics and Physics of Solids, Jan 1, 2009

The strong-contrast formulation is used to predict the effective conductivity of a porous materia... more The strong-contrast formulation is used to predict the effective conductivity of a porous material. The distribution, shape and orientation of the two phases are taken into account using two- and three-point probability distribution functions. A new approximation for the three-point probability function appropriate for two-phase media is proposed and discussed. Computed results for the effective conductivity using the strong-contrast formulation are compared to the Voigt and the Hashin-Shtrikman upper-bound estimates. These results show that the predicted effective conductivity is lower than both Voigt and Hashin-Shtrikman bounds. Compared to previous results using the weak-contrast formulation, the strong-contrast formulation seems to provide a better estimate for the effect of the microstructure on the conductivity.

International Journal of Solids and Structures, Jan 1, 2009

Statistical continuum theory based approaches are commonly used for the computation of the effect... more Statistical continuum theory based approaches are commonly used for the computation of the effective properties of heterogeneous materials. Statistical distribution and morphology of the microstructure are represented by n-point probability function. One-point probability function statistical representation of the microstructure leads to volume fraction dependent homogenization. However, second and higher order probability functions include the information of phase distribution and morphology. Most statistical based homogenization methods are limited to two-point probability function due to the lack of simple approximation of higher order probability functions that can be easily exploited. In this paper, a new approximation of the three-point probability function is proposed and discussed. The new approximation results are compared to existing approximations from the literature and to the real probability functions calculated from a computer generated two-phase micrographs.