Alexandre Vivet

Université de Caen Normandie | UNICAEN · Centre de Recherche sur les Ions, les Matériaux et la Photonique (CIMAP)

Using first-principle calculations, we have investigated the chemical functionalization of (8,0) zigzag single wall carbon nanotubes (SWNTs) by the amine group on Stone–Wales (SW) defects. The binding of NH2 with the defective (8,0) nanotube was explored and the preferential grafting sites have been identified. On the other hand, the modifications...

This article proposes an alternative way to use carbon nanotubes to improve the performance of carbon fibre-reinforced composites. A chemical process, based on esterification of surface groups, is used to anchor nanotubes onto carbon fibre surface. Anchored nanotubes form a network surrounding the carbon fibres. After CNT anchoring, the tow is impr...

A simple method is developed for grafting carbon nanotubes (CNTs) onto a carbon fiber surface. CNT and carbon fiber undergo an oxidation treatment. Oxidation generates oxygen, like carboxyl, carbonyl or hydroxyl groups, or amine groups on nanotubes and carbon fiber surface. Functionalized CNTs are dispersed in a solvent and deposited on carbon fibe...

La société Lineo NV produit des pré-imprégnés lin/époxyde destinés à un renfort unidirectionnel. Les fils de lin utilisés proviennent de l'industrie textile traditionnelle. Les propriétés mécaniques des quatre premiers modèles de pré-imprégnés élaborés ont été étudiées. L'évolution de la production a pour but de diminuer l'épaisseur des pré-imprégn...

A phenomenological 3D anisotropic nonlinear fatigue damage model has been developed for a short glass fiber-reinforced polyamide. The model is formulated within the framework of continuum damage mechanics and is based on a proposed anisotropic hyperelastic strain energy function. The proposed model accounts for the effects of fiber content and nonl...

The present paper proposes a mathematical development of the plasticity and damage approaches to simulate sheet metal forming processes. It focuses on the numerical prediction of the deformation of the sheet metal during the deep drawing process when a crack appears. Anisotropic plasticity constitutive equations are proposed. A fully implicit integ...

Composites reinforced with plant fibers have a high potential for valorization in new industrial applications, due to their good specific mechanical characteristics, their low cost and their availability. In order to accelerate their wide use in the industrial field, it is essential to improve their behaviour and durability in longterm atmospheric...

Developing an efficient non-associated plasticity criterion fully coupled with isotropic ductile damage is the main contribution of the current research. Two ductile degradation functions with variable degradation exponents are considered in this model, one for elasticity and the other for plasticity. Mixed (isotropic/kinematic) hardening rule and...

The main objective of this paper is to develop a numerical model susceptible to solve the numerical locking problems that may appear when applying the conventional solid and shell finite elements of ABAQUS. This model is based on a hexahedral solid shell element. The formulation of this element relays on the combination of the enhanced assumed stra...

In this paper, we propose an experimental and numerical model to study the creep behavior of the unidirectional Alfa fiber composite strength by the photoelasticity method. To have better mechanical properties, chemical treatment is made for Alfa fibers. Tensile tests are made to predict the Young modulus and tensile strength. These tests confirm t...

A model, based on the Van Wyk model, is developed to predict the compaction behaviour of stack sequence of dry fabric plies, and is used a set of 3 parameters (stiffness k, pressure sensitivity n and initial fibre ratio Vf0) with P = (k(Vf- Vf))n. The method originality is to construct the behaviour law of a complex stack sequence by the assembly o...

Because the timber market is more and more competitive, the particleboard manufacturers are looking for new sources of plant raw material. In the same time, the use of healthier, safer and more environmentally friendly materials becomes a priority in the building sector. In this context, using bio-based adhesives to bond the particles instead of th...

This study is focusing on the finite element simulation of low velocity impact applied to glass fiber-reinforced composites. Elasto-visco-plasticity is adopted taking into account strain rate effect, with isotropic hardening. To avoid numerical locking, hexahedral solid shell finite element SS is developed. The formulation is based on the mixed Ass...

Plant fiber properties, such as morphological and mechanical, are characterized by a large dispersion. Thereby, a statistical analysis is needed to obtain consistent results. An experimental study, conducted on 50 flax yarns, shows that the flax yarn properties (Young's modulus, tensile strength and diameter) follow Gaussian distributions. This app...

The objective of the present paper is to predict numerically the effect of low velocity impact on the composite epoxy reinforced with quasi-unidirectional flax fabrics. The composite circular plate is meshed with a solid shell finite element (SS). Only one element in the thickness direction is adopted. This SS element is implemented into the user e...

The purpose of this work was to analyse the damage process resulting from buckling load applied on composites reinforced by flax fibre. Continuous buckling tests were performed on specimens until cracks appeared on their outer face. These tests were monitored with an acoustic emission system. The high sensitivity of this method allows the detection...

This paper proposes to assess, in a multi-scale experimental approach, the hygroscopic expansion coefficients of flax yarns in radial direction and of flax fibre reinforced composites in the three directions (longitudinal, transverse and out of plane). Results show a significant flax yarn radial swelling coefficient (βr=1.06) and a composite highly...

Composites reinforced with plant‐based fibers present a high potential for valorization in new industrial applications due to their good specific mechanical characteristics, renewability, and recyclability. In order to accelerate their wide industry adoption, it is critical to assess their behavior and durability in heat and humid environments. Thi...

The main objective of this work is to develop an hexahedral solid shell finite element in order to resolve the numerical locking effects that may have occurred when employing the conventional solid and shell finite elements. The developed formulation relay on the coupling between the Assumed Natural Strain (ANS) and Enhanced Assumed Strain (EAS) me...

Dans ce travail, nous présentons les résultats de la caractérisation d'un matériau biocomposite (polypropylène / fibre d'alfa courte), pour différents niveaux de fibres (0%, 15% et 30%) non traitées et traitées à l'anhydride maléique. Pource faire, des échantillons ont été fabriqués conformément à la norme ISO 3167-A et testés sous charge statique....

In order to analyse the influence of conditioning at relative humidity on the behaviour of flax fibre reinforced composites, a preliminary study on flax fabrics needs to be conducted. Therefore, this paper investigates the effect of conditioning on the tensile properties of non-impregnated flax fabrics at different humidities. These fabrics are use...

Based on experimental test results, flax fiber reinforced polymer composites are characterized by nonlinear visco-elastoplastic behavior. The aim of this work is to model the quasi-unidirectional flax fiber reinforced composite behavior through a three dimensional formulation with orthotropic elasticity and orthotropic plasticity using Hill criteri...

In the past decades, research was directed towards the use of plant fibres instead of synthetic fibres as reinforcement of composites. Due to their high specific mechanical properties coupled with low cost and their wide availability at the European scale, flax fibres could be considered as the most interesting plant fibres. Experimental tests carr...

The purpose of this work is the improvement of flax fiber-reinforced composites obtained by vacuum molding in order to encourage their insertion into industrial products. The relatively high degree of porosity in these kinds of composites, due to the lack of compatibility between epoxy matrix and flax fibers and the hydrophilicity of flax fiber, re...

In this paper, several rigorous numerical simulations were conducted to examine the relevance of mean-field micromechanical models compared to the Fast Fourier Transform full-field computation by considering spherical or ellipsoidal inclusions. To be more general, the numerical study was extended to a mixture of different kind of microstructures co...

Nowadays, the prediction of mechanical behaviour of reinforced composites is a paramount problem in computational materials science. The macroscale effective coefficients are obtained from the microscale information also known as the so-called corrector problem. A numerical strategy based on integral equation known as the periodic Lippmann-Schwinge...

In this feature paper, we first review the state-of-the-art of experimental techniques and measurements to characterize the mechanical properties of anisotropic vegetal alfa-fibers, epoxy-resin and the behavior of the interphase between matrix and alfa fiber. Second, we conduct experimental tests to determine the mechanical properties of both fiber...

The aim of this work is to establish simple rules to optimise the architecture of plant woven fabric reinforcement for structural composite applications (sorption and mechanic aspects). For that, the influence of architectural parameters of reinforcement such as the frame, the yarn diameter, the pick count, and the filling rate, was studied from si...

This paper focuses on the load transfer improvement caused by nanofibers (NF) in carbon fiber reinforced composites. Load transfer is defined as the ability to transfer the mechanical loading between two adjacent fibers through the surrounding matrix. NF action is explored with a finite element model representing two carbon fibers separated by a la...

The agriculture in France offers exceptional wastes that can be recycled and turned into biomaterials. This paper presents a comparison between the properties of particleboards made from different agricultural wastes (hemp and flax shives, sunflower bark and rape straw) and those of classical particleboards based on wood. The use of these new agror...

Le comportement sous chargement monotone des composites renforcés par des fibres naturelles commence à être assez bien connu aujourd'hui. Cependant, le comportement à la rupture est encore mal maîtrisé. Le présent travail décrit une approche numérique développée pour simuler le mécanisme de propagation d'une fissure matricielle à l'interface fibre...

L'agriculture française propose des ressources remarquables pas ou peu exploitées et pouvant être valorisées en agromatériaux. Cette étude propose une comparaison des propriétés de panneaux de particules agglomérées réalisés à partir de différentes agroressources : le bois, la chènevotte, les anas de lin, l'écorce de tige de tournesol et la paille...

Flax fibre reinforced polymers are at the heart of current scientific and societal concerns. However their mechanical behaviour is still poorly known despite significant scientific efforts, in particular the non-linear behaviour observed under tensile tests. In this paper, results of hardening, creep and repeated progressive tests under uniaxial lo...

Composites of carbon nanotubes (CNT) in polymeric matrices have attracted considerable attention in the research and industrial communities due to their interesting and unique properties. However, the main intrinsic problem of CNT is their insolubility or very poor solubility in either water or organic solvents. Therefore, the dispersion of CNT has...

In this paper, an analytical solution is developed for free vibration analysis of conical fiber metal shells. In order to find constitutive relations, the assumptions of thins hells are used and the governing equations are based on Love’s theory. The Galerkin method is employed to solve the governing equations in which beam functions are used to ap...

The paper deals with the assessment of the influence of morphological parameters of a 2D random short fibre composite on its effective elastic properties. A double-scale 2D finite element approach is used and periodic representative volume elements are generated according to the model with an n-order approximate geometry. This one is a recent and p...

The aim of the present work is to study the effect of conventional textile treatments of woven flax on the mechanical properties and the water sorption of flax/epoxy composites. The flax fabrics are standard 2/2 twills. Various treatments are carried out on fabric such as mercerization, bleaching, and leaching for long fibers or on yarn such as lea...

We have investigated the sidewall functionalization of several (n, 0) zigzag Single Wall Carbon Nanotubes (SWNTs) by the hydroxyl, amine and carboxyl groups with n varying from 5 to 23 by using ab initio calculations. The results show that the stability of the OH, NH2 and COOH groups depends on the size of carbon nanotubes. The binding energies and...

An investigation of the influence of the carbon nanotube (CNT) agglomeration on the effective mechanical properties of CNT-based polymer composites is proposed. The study is based on a finite element (FE) analysis and a stochastic generation of 2D representative volume elements (RVE) in which both the distribution of the inclusions and a complete s...

The theme of my research is the study of interactions between the manufacturing process, the microstructure and the properties of materials. Since 2004, I have focused on the incorporation of nanoparticles into polymer materials and carbon fiber reinforced composites. Several keywords summarize the backbone of my work: * measurement of the effectiv...

We present a numerical investigation of the elastic coefficients of random fibre composites with high contrast of properties. Here we consider a numerical study based on the generation of representative volume elements (RVEs) with overlapping random fibre network. Such a concept requires an important Monte-Carlo draw of patterns as well as an accur...

Using ab initio calculations, we have investigated the sidewall functionalization of several (n,0) zigzag single wall carbon nanotubes (SWCNTs) by the amine group with n varying from 5 to 23. The results show that the stability of the NH2 group depends on the size of carbon nanotubes. The binding energies and structural properties have been determi...

Dans ce travail, afin d'améliorer les propriétés mécaniques des composites lin/époxy, des traitements chimiques ont été testés. Les fibres de lin subissent divers traitements pour des applications destinées au secteur textile : blanchiment, mercerisation, lessivage, traitement enzymatique ou traitement enzymatique avec détergent. Les composites ont...

Nous présentons une approche stochastique multi-échelle pour évaluer les propriétés mécaniques effectives de matériaux composites matrice polymère/nanotubes de carbone (NTC). Les effets sur le comportement mécanique des matériaux composites de différentes caractéristiques des NTC, comme la longueur, le diamètre, le taux volumique et la dispersion,...

Dans ce travail, afin d'améliorer les propriétés mécaniques des composites lin/époxy, des traitements chimiques ont été testés. Les fibres de lin subissent divers traitements pour des applications destinées au secteur textile : blanchiment, mercerisation, lessivage, traitement enzymatique ou traitement enzymatique avec détergent. Les composites ont...

Un banc d'essai de micro-traction est utilisé pour tester la traction de fibres élémentaires de lin. Les champs de déplacements de la fibre sont calculés en temps réel par une technique de corrélation d'images numériques. Ceci permet de discriminer les essais visiblement défectueux. Les déformations longitudinales sont issues de ces champs de dépla...

RESUME: Le présent travail a pour objectif le développement d'une méthode simple de greffage des nanotubes de carbone (NTC) sur la surface de fibres de carbone. Le greffage de NTC doit améliorer les propriétés interfaciales de composite résine époxyde/fibre de carbone. La fonctionnalisation des NTC est effectuée par un traitement acide (HNO 3 /H 2...

The present work investigates the hysteretic behaviour of Cu-Zn-Al single crystal submitted to superelastic shear tests. Major symmetric loops were performed within the shear strain limit of the stress-induced martensitic transformation. Minor loops inside the major loops allowed to analyse more closely the hysteretic behaviour of the Cu-Zn-Al sing...

The finite element modeling is used to improve the accuracy of In composition determination by taking into account the two limiting factors in high resolution microscopy: strain relaxation and projection.

Biaxial proportional loading such as tension (compression)–internal pressure and bi-compression tests are performed on a Cu-Zn-Al and Cu-Al-Be shape memory polycrystals. These tests lead to the experimental determination of the initial surface of phase transformation (austenite→martensite) in the principal stress space (σ1,σ2). A first “micro–macro...

Using strain analysis on high resolution electron microscopy images and finite element modeling of InGaN quantum wells (QWs), it is shown that the In composition changes inside the layers can be accurately determined. The analyzed samples were nominally grown with 15%–17% In composition by molecular beam or metalorganic vapor phase epitaxy. Inside...

On one hand, bi-compression tests and tension (compression)-internal pressure tests on a Cu-Al-Be shape memory alloy (SMA) polycrystals permit the determination of the yield surface of phase transformation initiation (Austenite → Martensite). On the second hand, the lattice measurements of the L21 austenite and the monoclinic martensite cells for t...

Like in the plasticity theory, the prediction of phase transformation yield surfaces constitutes a key point in the modeling of polycrystalline shape memory alloys thermomechanical behavior. Generally in some micro-macro integration, the nature of the interface between austenite and twinned or untwinned martensite under stress free state and the ch...

Colloque National Mecamat, Aussois, France, 20-24 janvier

On one part, lattice parameters of a 66.84Cu 23.73Zn 9.4Al at.% alloy in austenite A and martensite M phases are measured. Using the mathematical crystallographic theory of the phase transformation, the nature of the phase transformation is determined. One obtains thus an exact interface between parent phase and untwinned martensite like the shape...

On one hand, the lattice measurements of the austenite and the martensite cells for one CuZnAl and one CuAlBe alloys permit to determine the nature of the phase transformation i.e. an "exact" interface between the parent phase and an untwinned martensite variant. Hence, for single crystals, the yield surface looks like a polygon with several sector...

CuZnAl single crystals were thermomechanically treated to test their shear and tensile pseudoelastic behaviors. Despite the technological difficulties inherent to shear test setting, interesting results were reached. Due to the low crystallographic symmetry of martensite, the first stress-induced variant is a function of both the mechanical loading...