Defining a reduced volume zone for the simulation of burst test on a composite pressure vessels

International audience; A Fibre-Break Model (FBM) developed at Mines ParisTech can predict the burst pressure of high pressure composite vessels. This model uses random values of fibre strength at each Gauss point of the considered vessels meshed with finite element (FE). However, previous studies has determined the optimum FEs to be used on real-scale structures (0.1 mm x 0.1 mm x 8 mm). A simple calculation shows that, on a real-scale pressure vessel, this induces a gigantic number of FEs, hence the extensive computation time. To overcome this problem, the integral range method is proposed to find a reduced volume zone of the vessels, on which an equivalent calculation can be made and giv…

Fibre break processes in unidirectional composites

International audience; A model to predict the effects of the accumulation of fibre breakages in unidirectional carbon fibre composites has been developed that takes into account several physical phenomena controlling fibre failure, including the stochastic nature of fibre strength, stress transfer between fibres due to the shear of the matrix, interfacial debonding and viscosity of the matrix. The damage processes leading up to failure are discussed and quantified, first in terms of fibre breaks for the case of monotonically increasing tensile loading, then for sustained loading and finally the implications for more complex loads and structures are discussed. It is clearly shown that the f…

From fracture to damage mechanics: a behavior law for microcracked composites using the concept of crack opening mode

International audience; Many studies have been carried out in order to build a coherent macroscopic behavior law for a composite containing microcracks. All of them are only partially coherent and none of them is complete. This study proposes a hyperelastic behavior law for a microcracked composite, respecting all the conditions associated with the damage activation/deactivation, stress/strain relation continuity, induced anisotropy and the Clausius–Duhem inequality. This approach is based on the definition of the Crack Opening Mode for Damage Mechanics as it exists in Fracture Mechanics.

The application of a reduced volume method for the simulation of the characterisation of a carbon fibre pressure vessel

International audience; The characteristics of advanced composite materials make them ideally suited for use in pressure vessels for storing gas as fuel for ground transport vehicles. It has been found that the failure process starts with randomly distributed fibre breaks and as the loading continues, they coalesce into clusters of fibre breaks which lead to failure [4]. However, improvements are needed to reduce computational times when performing full-scale simulations. The reduced volume method is therefore applied to the stochastic fibre break model related to the concept of an integral range. This method allows the calculation for a certain volume of a laminate that statistically repre…

Micromechanics, damage and life prediction of carbon fibre composite pressure vessels

31 mai-3 juin 2004; International audience; A study by 3D finite element analysis has revealed the changes in the stress field around broken fibres in cfrp by considering the evolution of representative elementary volumes of the composite for both elastic and viscoelastic matrices and the effects of debonding. The viscoelastic behaviour of the matrix does not change the mechanism of load transfer but introduces time as a parameter. At a constant load, the relaxation of the matrix increases the coefficients of load transfer around broken fibres and causes new failures of fibres. This analysis relates the acoustic emission detected during steady loading to fibre failures. In this way a model …

Détection d'endommagement dans les composites fibres/résine à l'aide de la technologie micro-onde

National audience; On présente dans cet article une méthode novatrice de contrôle non destructif d'endommagement dans les matériaux composites. Elle est fondée sur l'observation et l'analyse des modifications des propriétés diélectriques d'un milieu dues à un endommagement. Plus précisément, son originalité réside dans le fait que le diagnostic cherché est obtenu via un circuit résonant microbande soumis à un champ électromagnétique dans la gamme des micro-ondes. Dans cet article on montre la faisabilité de la méthode sur la détection de la rupture des fibres d'une éprouvette en composite unidirectionnel soumise à un effort de flexion et on indique en quoi elle possède potentiellement des a…

Benchmarking of strength models for unidirectional composites under longitudinal tension

© 2018 Elsevier Ltd Several modelling approaches are available in the literature to predict longitudinal tensile failure of fibre-reinforced polymers. However, a systematic, blind and unbiased comparison between the predictions from the different models and against experimental data has never been performed. This paper presents a benchmarking exercise performed for three different models from the literature: (i) an analytical hierarchical scaling law for composite fibre bundles, (ii) direct numerical simulations of composite fibre bundles, and (iii) a multiscale finite-element simulation method. The results show that there are significant discrepancies between the predictions of the differe…

Micromechanisms of load transfer in a unidirectional carbon fibre–reinforced epoxy composite due to fibre failures. Part 1: Micromechanisms and 3D analysis of load transfer: The elastic case

This study gives a detailed analysis of load distributions around fibre breaks in a composite and the mechanisms involved in load transfer. In contrast to other studies reported in the literature the analysis considers different configurations of composite damage from the failure of a few fibres to the failure of many. The model considers the elastic case with and without debonding at the broken fibre/matrix interface. In this way, the usual limitations of the finite element approach are overcome so as to take into account the numbers and interactions of broken fibres whilst maintaining an evaluation of the various fields involved, in particular the stress fields associated with fibre failu…

Détection des ruptures de fibres et du délaminage dans les composites verre/époxy et carbone/époxy à l'aide de structures propagatives dans la gamme des micro-ondes = fibre breaks and delamination detection in composites by using propagative structures in the microwaves frequencies

National audience; On présente dans cet article la détection de ruptures de fibre et du délaminage dans les composites unidirectionnels verre/époxy et carbone/époxy en utilisant des structures propagatives électromagnétiques dans la gamme des micro-ondes.

Une methode générale de prévision du comportement viscoélastique des composites stratifiésGeneral methodology to predict viscoelastic behaviour of composite laminates

Resume On presente dans ce papier un outil ayant pour base la theorie classique des plaques et capable de prevoir le comportement viscoelastique d'un composite stratifie. Alors que la theorie initiale n'est valide que dans le cas ou le comportement des plis est elastique lineaire, on montre que lorsque le comportement des plis est viscoelastique il est encore possible de conserver l'avantage de la souplesse d'emploi et de mise en œuvre de cet outil largement utilisee par les industriels. Des comparaisons entre des resultats obtenus a l'aide de ce nouvel outil et des resultats experimentaux mais egalement avec des calculs par elements finis montrent la pertinence de la methode.

Three-dimensional analysis of load transfer micro-mechanisms in fibre/matrix composites

International audience; This study gives a detailed analysis of load distributions around fibre breaks in a composite. In contrast to other studies reported in the literature, the analysis considers different configurations of composite damage from the failure of a few to the failure of many fibres. The model considers three types of matrix behaviours (elastic, elastic–plastic and viscoelastic) with or without debonding at the broken fibre/matrix interface. In this way, the usual limitations of the finite element approach are overcome so as to take into account the number and interactions of broken fibres whilst maintaining an evaluation of the various fields (stresses in particular).

Effect of the Time Dependent Loading of Type IV Cylinders using a Multiscale Model

International audience; The current requirements for composite cylinders are still based on an arbitrary approach derived from the behaviour of metal structures, that the designed burst pressure should be at least 2.5 times the maximum in-service pressure [1]. This could lead to an over-designed composite cylinder for which the weight saving would be less than optimum. Moreover, predicting the lifetime of composite cylinders is a challenging task due to their anisotropic characteristics. A federal research institute in Germany (BAM) has proposed a minimum load-cycle requirement that mitigates this issue by using a Monte-Carlo analysis of the burst test results [2-3]. To enrich this study, m…

Proof testing and lifetime reliability of carbon fibre reinforced composite pressure vessels

International audience

Conceptualisation et classification des problèmes de fatigue mécanique

International audience; On propose de conceptualiser et de classifier les problèmes de calcul de structures dits de fatigue (dans le cadre de la Mécanique de lʼEndommagement). Parce que le concept de fatigue est avant tout un concept que lʼon peut estimer structural plutôt que local, cette classification est faite dʼabord sur des grandeurs structurales. Ensuite, on donne une classification faite sur des grandeurs locales. Lʼobjectif de ces classifications est de favoriser la résolution locale des problèmes de fatigue dʼune classe donnée en aidant à la justification du passage des lois dʼévolution obtenues par la Thermodynamique à celles écrites dans le cadre de la fatigue.

Modelling an Improved NOL Ring Test Using a Reduced Volume Method for the Characterisation of Composite Cylinders

International audience

Modélisation des composites microfissurés. Utilisation d'un nouveau concept pour la mécanique de l'endommagement inspiré de la mécanique de la rupture

National audience; On propose dans cette étude un modèle de comportement d'un milieu composite microfissuré formulé de manière tridimensionnelle, qui résout l'ensemble des contraintes théoriques indispensables à la cohérence d'un modèle, notamment, le respect de la condition de contact unilatéral et la prise de l'anisotropie induite. Pour parvenir à ce résultat, on a étendu à la Mécanique de l'Endommagement, la notion de Mode d'Ouverture d'une fissure qui existe en Mécanique de la Rupture.

Effect of the loading rate on ultimate strength of composites. Application: Pressure vessel slow burst test

International audience; The strength of unidirectional elastic fibre composites is shown to depend on the loading rate as the viscoelastic nature of the matrix results in a fall in breaking load as the rate is reduced. The simulation of the accumulation of fibre breaks leading to failure, takes into account all physical phenomena involved fibre failure, including the stochastic nature of fibre strength, stress transfer through the matrix between reinforcements, interfacial debonding and the viscoelastic nature of the matrix. The kinetics of composite failure are seen to involve the initial formation of random fibre breaks which at higher loads coalesce into clusters of broken fibres. The ra…

A new invariant-based method for building biomechanical behavior laws - Application to an anisotropic hyperelastic material with two fiber families

Abstract In this article, we present a general constructive and original approach that allows us to calculate the invariants associated with an anisotropic hyperelastic material made of two families of collagen fibers. This approach is based on mathematical techniques from the theory of invariants: • Definition of the material symmetry group. • Analytical calculation of a set of generators using the Noether’s theorem. • Analytical calculation of an integrity basis. • Comparison between the proposed invariants and the classical ones.

Mécanique et comportements des milieux continus : tome 1 Concepts généraux

Cet ouvrage de Mécanique des milieux continus a pour but essentiel de vouloir rendre accessibles et opérationnels pour tout public (étudiants, chercheurs et ingénieurs), les notions et les outils nécessaires à une construction des modèles de milieux continus et de leurs lois de comportement. Tous les développements sont très détaillés afin de ne laisser aucune zone d'ombre quant à l'obtention des résultats mais également pour permettre au lecteur l'apprentissage et l'acquisition de techniques de calculs.

Analyse multiéchelle d'un composite textile = Multiscale analysis of a textile composite

National audience; On propose dans cette étude de comprendre le comportement mécanique d'un composite textile. Pour ce faire, l'étude se scinde en deux parties distinctes. Dans cet article, nous présentons la modélisation multiéchelle qui fait suite à une étude expérimentale. Son objectif est double : comprendre la nature du comportement macroscopique observé et expliquer l'origine des endommagements susceptibles d'apparaître. L'étude expérimentale du matériau fait l'objet d'un premier article.

Damage in composites : from physical mechanisms to modelling

International audience; The most critical types of damage in composite materials are transverse cracking, delamination and fiber breaking. The simulation of the behaviour and the rupture of these materials shows that it is important to consider failure mechanism in the design of structures. Each mechanism induces local deteriorations which can be accelerated when they are coupled with other mechanisms. Global criteria are unable to predict neither these processes nor their interactions. This paper is an attempt to propose realistic criteria which are the witness of local degradations and can be used for the design of composite structures.

Détection de ruptures de fibres au sein d'un composite unidirectionnel à l'aide d'un circuit micro-onde résonant

International audience; Cet article présente une méthode novatrice de controle non destructif d'endommagement dans les matériaux composites. Elle est fondée sur l'observation et l'analyse des modifications des propriétés diélectriques d'un milieu dues à un endommagement. Plus précisément, son originalité réside dans le fait que le diagnostic cherché est obtenu via un circuit résonant microbande soumis à un champ électromagnétique dans la gamme des micro ondes. Cet article démontre la faisabilité de la méthode sur la détection de la rupture des fibres d'une éprouvette en comosite unidirectionnel soumise à un effort de flexion et indique en quoi elle possède potentiellement des atouts pour et…

Matériaux composites soumis à de grandes vitesses de sollicitation

International audience; L'objet de ce travail est de modéliser la réponse à des sollicitations quasi-statiques et dynamiques de deux matériaux composites utilisés dans l'industrie automobile : un tissu verre/polypropylène et une matrice polypropylène renforcée de fibres courtes en verre. Pour ce faire, des essais mécaniques à différentes vitesses de sollicitation (de 10-4s-1 à 100s-1 ) ont été menés. La campagne expérimentale nous a permis d'identifier pour chacun des matériaux les phénomènes dissipatifs prépondérants et de quantifier leur part dans la déformation totale, en fonction de la vitesse. Nous proposons ensuite un modèle unifié de comportement permettant de répondre de manière coh…

Elévation de température au sein d'une éprouvette de polyamide sous sollicitation de traction

The control of the residual lifetimes of carbon fibre-reinforced composite pressure vessels

International audience; The understanding of the degradation of carbon fibre composites, with emphasis on the use of these composites in filament-wound pressure vessels, is explored. Earlier studies by many researchers have led to a general appreciation of the mechanisms involved; however, only recently have both computational power and experimental techniques become sufficiently developed to allow for the use of quantitative analyses. It is shown that damage is controlled by fibre failure, and that initially this occurs randomly within the structure. In monotonic loading, the development of clusters of fibre breaks causes rapid failure; however, under maintained loads the kinetics of damag…

Durability of a 3D woven composite assisted by finite element multi-scale modelling

International audience; The textile composite studied is a 3D woven composite. A unit cell is defined by using microscopic examinations of the microstructure. A multiscale approach assisted by the finite element method is performed in order to estimate the effective properties of the composite and then to access to local stress field. This approach allows the determination of the kind of load to which warp yarns are subjected. Moreover, detailed analysis of damaged model using different configurations of broken yarns are treated. The evolution of the stress concentration coefficient highlight the load transfers due to consecutive yarn breaks.

Suivi de l'endommagement dans les structures en composites par une analyse optique in-situ

National audience; Ce travail présente une technique de détection et de suivi de l'endommagement dans les structures en matériaux composites. Les mécanismes d'endommagement dans ces matériaux sont complexes. Dès lors que l'on souhaite modéliser le comportement d'une structure, il est important de comprendre comment celle-ci s'endommage. La méthode optique d'observation in-situ proposée est appliquée au cas d'une plaque trouée.

Détection d'endommagement dans les composites à l'aide de la technologie micro-onde

6-8 juin 2007; National audience

Détection et discrimination par émission acoustique des endommagements dans les composites. Comparaison expérience / modélisation

International audience; On présente dans cette étude la discrimination des phénomènes de ruptures de fibre, de microfissuration intralaminaire, de macrofissuration intralaminaire ainsi que du microdélaminage au sein des composites stratifiés d'unidirectionnels orientés, dans le cadre d'une méthode de détection des endommagements basée sur la technique de l'Emission Acoustique. Ces résultats expérimentaux sont confrontés aux prévisions issues d'un modèle de comportement de matériaux composites unidirectionnels, basés sur la physique des phénomènes à l'échelle des constituants.

7.22 Health Monitoring of High Performance Composite Pressure Vessels

The most important form of damage in carbon fiber reinforced composite pressure vessels is the failure of the fibers however the rate of fiber failure is controlled by the viscoelastic nature of the matrix, which determines overall in-service lifetimes. This type of damage is very different from that encountered with metal pressure vessels and requires a detailed understanding in order to ensure reliability. Innovative proof testing methods based on these processes are necessary. The damage processes and the means of quantifying them are discussed. Their reliability under pressure over periods of decades is analyzed. Intrinsic safety factors linked directly to the properties of the composit…

Quantifiable analysis of the failure of advanced carbon fibre composite structures leading to improved safety factors

Abstract The increasing use of advanced composite materials means that they must now be considered as major materials for a wide variety of structures some of which will be in service for decades. There is therefore an important need to be able to quantify damage accumulation leading to failure in these materials particularly as they are often used in extreme situations for which failure must be avoided. This review shows how damage accumulation in many major composite structures is dominated by fibre failure but that the viscoelastic nature of the matrix induces time effects including delayed failure. It is shown that damage accumulation can be quantitatively modelled using a multi-scale a…

Simulation numérique du confort de sièges d'automobiles : comportement mécanique 3D de mousses de polyuréthanne ; optimisation 2D d'un profil simplifié de siège

Resume Dans cet article, le comportement mecanique de differentes mousses de polyurethanne (PU) est etudie. Une attention particuliere est portee sur la dependance par rapport au temps du comportement de ces dernieres, sous les hypotheses de la theorie des grandes deformations. Des tests experimentaux selectionnes parmi une base de donnee experimentale comprenant des essais de compression uniaxiale (en cyclage et relaxation) et des essais de cisaillement simple sont presentes. Une loi de comportement phenomenologique est developpee et utilisee pour modeliser le comportement mecanique de ces mousses polymeriques. La validation numerique de la loi de comportement utilisee est decrite grâce a …

Prédiction de la contrainte de rupture de composites unidirectionnels et suivi de l'accumulation de ruptures de fibres

Micromechanisms of load transfer in a unidirectional carbon fibre–reinforced epoxy composite due to fibre failures. Part 2: Influence of viscoelastic and plastic matrices on the mechanisms of load transfer

A local three-dimensional (3D) finite element analysis (FEA), of the mechanisms governing composite damage (in the region around a fibre break), has been carried out. The model considers viscoelastic and plastic matrix behaviours with and without debonding at the broken fibre/matrix interface. The finite element analysis has shown that even a simple viscoelastic law describing the behaviour of the epoxy resin leads to an increasing load on the neighbouring intact fibres, as a function of time. The plastic behaviour of the matrix has been shown to have consequences on reloading after unloading. In contrast to other studies reported in the literature, the calculations were carried out on diff…

Health monitoring of high performance composite pressure vessels,

International audience; The most important form of damage in carbon fiber reinforced composite pressure vessels is the failure of the fibers however the rate of fiber failure is controlled by the viscoelastic nature of the matrix, which determines overall in-service lifetimes. This type of damage is very different from that encountered with metal pressure vessels and requires a detailed understanding in order to ensure reliability. Innovative proof testing methods based on these processes are necessary. The damage processes and the means of quantifying them are discussed. Their reliability under pressure over periods of decades is analyzed. Intrinsic safety factors linked directly to the pr…

Visual indicator for the detection of end-of-life criterion for composite high pressure vessels for hydrogen storage

International audience; A model to predict the accumulation of fibre breaks in advanced composites, that takes into account all physical phenomena implicated in fibre failure (i.e. the random nature, stress transfer due to breaks, fibre debonding and viscosity of the matrix) shows clearly that the failure of a unidirectional composite structure results in the formation of random fibre breaks which at higher loads coalesce into clusters of broken fibres. This stage of development is followed almost immediately by failure. This has direct application to filament wound pressure vessels of the type used to store hydrogen under high pressure. A novel, cost effective, method of revealing developi…

A constructive approach of invariants of behavior laws with respect to an infinite symmetry group – Application to a biological anisotropic hyperelastic material with one fiber family

Abstract In this paper, six new invariants associated with an anisotropic material made of one fiber family are calculated by presenting a systematic constructive and original approach. This approach is based on the development of mathematical techniques from the theory of invariants: • Definition of the material symmetry group. • Definition of the generalized Reynolds Operator. • Calculation of an integrity basis for invariant polynomials. • Comparison between the new (constructed) invariants and the classical ones.

Micromechanisms of load transfer in a unidirectional carbon fibre-reinforced epoxy composite due to fibre failures: Part 3. Multiscale reconstruction of composite behaviour

International audience; This third article describes a multiscale process which takes into account the most important microscopic phenomena associated with composite degradation, including fibre fractures and interfacial debonding, overloading of fibres neighbouring a fibre break as well as viscoelastic behaviour of the matrix. The results have been used to accurately predict the macroscopic failure of unidirectional carbon fibre-reinforced epoxy and quantify damage accumulation in pressure vessels made of the same material. The approach described has allowed the acoustic emission activity resulting from fibres breaks to be evaluated and shown how the residual lifetimes of such vessels, whe…

Modelling unilateral damage effect in strongly anisotropic materials by the introduction of the loading mode in damage mechanics

Abstract Damage weakens the mechanical characteristics of materials. But this weakening can disappear if the cracks close again: this is called the unilateral effect of damage. We propose a model of this phenomenon using damage mechanics in the case of a diffuse network of identical microcracks. The microcracks state is defined with two internal state variables. These two variables are control parameters of the geometry of the microcracks. They also define the loading mode in damage mechanics as in fracture mechanics. In order to limit the anisotropy induced by the microcracks, hence by the loading, we suppose that the geometry of damage spreads into preferential directions. Therefore, this…

Elévation de température au sein d'une éprouvette de polyamide sous sollicitation de traction dynamique

National audience

Fibre breakings detection in unidirectional composites using microwave technology

International audience

Analytical and finite element analyses on reliability of carbon fibre reinforced plastics

International audience

Détection d'endommagement dans les composites à l'aide des micro-ondes. Comparaison avec la thermographie infrarouge

International audience; On compare dans cette étude deux méthodes de détection d'endommagement dans les composites : une basée sur la technologie des structures propagatives électromagnétiques dans la gamme des micro-ondes et l'autre basée sur la mesure de champs thermiques dans la gamme des infrarouges. Toutes deux sont appliquées à la détection des ruptures de fibres et du délaminage dans des composites fibres/résine de type verre/époxy et carbone/époxy.

Pour une approche locale de la fatigue : proposition d'une conceptualisation et d'une classification des problèmes de fatigue

International audience; Dans cette étude, on propose de conceptualiser et de classifier les problèmes de calcul de structures dits de fatigue (dans le cadre de la Mécanique de l'Endommagement). Parce que le concept de fatigue est avant tout un concept que l'on peut estimer structural plutôt que local, cette classification est faite d'abord sur des grandeurs structurales. Ensuite, on donne une classification faite sur des grandeurs locales. L'objectif de ces classifications est de favoriser la résolution locale des problèmes de fatigue d'une classe donnée en aidant à la justification du passage des lois d'évolution obtenues par la Thermodynamique à celles écrites dans le cadre de la fatigue.

Mécanique du point (Cours et travaux dirigés)

Détection d'endommagement dans les composites à l'aide d'une technologie utilisant des micro-ondes et par thermographie infrarouge

National audience; On présente dans cette étude deux méthodes de détection d'endommagement dans les composites : une basée sur la technologie des structures propagatives électromagnétiques dans la gamme des micro-ondes et l'autre basée sur la mesure de champs thermiques dans la gamme des infrarouges. Toutes deux sont appliquées à la détection des ruptures de fibres et du délaminage dans des composites fibres/résine de type verre/époxy et carbone/époxy. La méthode par micro-onde est fondée sur les modifications des propriétés diélectriques d'un milieu lors d'un endommagement. Elle analyse les modifications de l'onde réfléchie d'une onde transmise dans le matériau vue comme une structure prop…

Modelling the effect of porosity on the mechanical properties of unidirectional composites. The case of thick-walled pressure vessels

International audience; The present article highlights morphological features present in composite pressure vessels. The use of X-ray microtomography provides three-dimensional information about the voids in a large thick-walled type 3 pressure vessel at the mesoscopic scale. The observations show that the porosity structure depends strongly on composite thickness and orientation. A numerical approach is proposed to model realistically the damage phenomena in pressure vessels.

Mécanique du Solide (Cours, exercices et problèmes corrigés)

Prédiction du comportement mécanique et étude de l’endommagement d’un composite tressé 3D par une analyse multiéchelle. Application à la conception de réservoirs pour véhicules GNV

Cette étude porte sur la prédiction du comportement mécanique et l’étude de l’endommagement de composites tressés 3D, utilisés pour fabriquer des réservoirs multiformes. D’une part, on cherche à prédire les propriétés effectives du matériau homogénéisé par une approche dite d’homogénéisation multiéchelle à partir de la connaissance des propriétés des constituants, de leur fraction volumique et de leur disposition au sein d’un élément de volume représentatif du matériau hétérogène communément appelé volume élémentaire représentatif (VER). D’autre part, on cherche à avoir accès à des grandeurs locales pour mieux comprendre les mécanismes d’endommagement identifiés expérimentalement et évaluer…

Détection et discrimination par émission acoustique des endommagements dans les composites stratifiés d'unidirectionnels ; rupture de fibre, macro et micro fissuration intralaminaire, microdélaminage. Comparaison expérience/modélisation

National audience; On présente dans cette étude la discrimination des phénomènes de ruptures de fibre, de microfissuration intralaminaire, de macrofissuration intralaminaire ainsi que du microdélaminage au sein des composites stratifiés d'unidirectionnels orientés, dans le cadre d'une méthode de détection des endommagements basée sur la technique de l'Emission Acoustique. Ces résultats expérimentaux sont confrontés aux prévisions issues d'un modèle de comportement de matériaux composites unidirectionnels, basés sur la physique des phénomènes à l'échelle des constituants. Plus précisément, ce modèle prend notamment en compte : le caractère aléatoire des ruptures de fibres, les transfert de c…

A methodology for the control of the residual lifetimes of carbon fibre reinforced composite pressure vessels

International audience; Pressure vessels must be periodically proof tested. Traditional techniques for metal vessels are inapplicable for composite vessels as the latter do not break by crack propagation so that the reasoning behind the traditional testing procedures is not appropriate. Damage accumulation leading to the degradation of a composite vessel is by fibre failure. Fibres show a wide distribution in strengths and loading a composite inevitably breaks some. The method which has been developed is supported by an analysis of delayed fibre failure due to the relaxation of the resin around fibre breaks. This provokes overloading of intact fibres neighbouring breaks. The time until a cr…

A simplified FE2 model of fibre failure and its consequences applied to the design of composite pressure vessels

International audience

Analyse multiéchelle d'un composite textile

National audience; On propose dans cette étude d'expliquer le comportement mécanique d'un composite textile au travers d'un processus multiéchelle. Les propriétés mécaniques nécessaires à la réalisation des calculs ont été déterminées par une étude expérimentale préalable.

Intrinsic mechanisms limiting the use of carbon fiber composite pressure vessels

International audience; The viscoelastic properties of the resins used in carbon fiber composite pressure vessels introduce time effects which allow damage processes to develop during use under load. A detailed understanding of these processes has been achieved through both experimental and theoretical studies on flat unidirectional specimens and with comparisons with the behavior of pressure vessels. Under steady pressures, the relaxation of the resin in the vicinity of earlier fiber breaks gradually increases the sustained stress in neighboring intact fibers and some eventually break. The rate of fiber failure has been modeled based only on physical criteria and shown to accurately predic…

Predicting mechanical behaviour and damage kinetics of a 3D interlock composite materials by using a multiscale approach

International audience; The present work aims to investigate the mechanical behaviour and the damage kinetics of a3D interlock woven fabric composite, especially used for natural gas tanks dedicated to thetransportation industry. On the one hand, we aim at predicting the macroscopic coefficients ofthe stiffness matrix by homogenization multiscale approach. For this, we identified a basicunit cell which represents well the composite microstructure. On the other hand, damagemechanisms are analyzed: optical microscopy examinations on damaged specimens revealedseveral types of defects. We used the same multi-scale approach to assess the impact of thesedefects on the decrease of stiffness.

Une nouvelle technique de détection des endommagements dans les composites basée sur l'utilisation des micro-ondes et des circuits microrubans résonants

Resume On presente dans cet article une methode non destructive novatrice de detection d'endommagement dans les materiaux composites. Elle est fondee sur l'observation et l'analyse des modifications des proprietes dielectriques d'un milieu dues a un endommagement. Plus precisement, son originalite reside dans le fait que le diagnostic cherche est obtenu via un circuit resonant microbande soumis a un champ electromagnetique dans la gamme des micro-ondes. Dans cette Note, on montre la faisabilite de la methode en examinant sa capacite a detecter les ruptures de fibres au sein d'une eprouvette en composite unidirectionnel soumise a un effort de flexion. Pour citer cet article : J. Rossignol, A…

Damage accumulation in a carbon/epoxy composite : Comparison between a multiscale model and computed tomography experimental results

International audience; High-resolution computed tomography has been carried out for carbon/epoxy laminates loaded in situ to failure. The experimental data allows major damage mechanisms to be quantified in 3D, in an unambiguous and mechanically representative way, where previous experimental analysis is limited. A multi-scale model that predicts damage accumulation in tensile loaded composites is compared to the experimental analysis, to validate the underpinning assumptions within the model and overall performance. The model considers the random nature of fibre-strengths, stress transfer resulting from fibre breaks, fibre/matrix debonding and viscosity of the matrix. Assumptions within t…

Indicateur visuel de l'état de fin de vie d'un réservoir composite

National audience

Bending effect on the risk for delamination at the reinforcement/matrix interface of 3D woven fabric composite using a shell-like RVE

This paper presents a computational homogenisation-based technique for flexural effects in textile reinforced composite planar shells. An homogenisation procedure is used for the in-plane and the out-of-plane behaviour of three-dimensional woven composite shells, taking the in-plane periodicity of the material into account while relaxing any periodicity tying in the thickness direction. Several types of damage (matrix or reinforcement cracking, delamination, …) can appear in a composite material. In this paper, material non-linear computations are used to assess the importance of bending on the risk for delamination at the reinforcement/matrix interface. The normal and tangential stresses a…

Damage accumulation and life prediction in carbon fibre composite pressure vessels

Composites and nanostructures

Determination of lifetime probabilities of carbon fibre composite plates and pressure vessels for hydrogen storage

International audience; It is shown that an analogy can be made between the failure of unidirectional carbon fibre reinforced epoxy plates and filament wound carbon fibre composite pressure vessels and that their strengths and failure probabilities can be determined. Fibres in filament wound composite structures are placed on geodesic paths around the mandrel, which becomes the liner; so that when the structure is pressurised the fibres are only subjected to tensile forces, as in a unidirectional composite. Multiscale modelling reveals that composite failure is controlled by fibre breakage and that clustering of fibre breaks determines ultimate reliability of the structure. Time dependent r…

A new constructive method using the theory of invariants to obtain material behavior laws

International audience; The aim of this paper is to present a constructive method to derive mechanical behavior laws using the Theory of Invariants and Continuum Thermodynamics. More precisely, we want to construct, in a general way, the state or dissipation potential in a polynomial form given a set of variables V and the material symmetry group S. For this purpose, we show how to obtain a set of generators for the S-invariant polynomials of V. Then, using the Grœbner basis concept, we write all the decompositions of a polynomial of a given degree.