Research Items (56)
This work aims to study experimentally and numerically the pressure behaviour of filament wound adhesively bonded interlocked tube under internal pressure tests. To this end, a series of hydraulic pressure tests were carried-out on E glass reinforced Vinylester 411 adhesively bonded tubes. The experimental results have revealed that a leakage was witnessed on the bonding area. Furthermore, the post-mortem X-ray tomography tests on specimens, subjected to internal pressure loading, provided a better understanding of the failure mechanisms resulting from the applied pressure. Based on these results, a finite element model was developed taking into account the nonlinearity behaviour of the adhesive layer. In fact, the aforementioned model intend a compliant prediction of the pressure behaviour of the joined tube as well as the damage propagation in the bonding zone. A perfect correlation of the experimental and the numerical outcomes has been obtained.
Magnetic properties of soft ferromagnetic materials are very sensitive to high mechanical and thermal stresses. In order to characterize its changing magnetic behavior, this chapter deals with the study of the choice of the performant magnetic hysteresis model, which can be able to model perfectly the thermo–magnet–mechanical coupling of a fully processed non-oriented Fe-3 wt%Si steel sheet. Therefore, our study focuses on identifying the model parameters for different static models by application of an appropriate optimization technique. For simple models, a direct identification is used, and the GA technique will be applied for complex ones. The performance of the model depends on the error that it presents with the measurements as well as its ability to reproduce properly the experimental hysteresis studied. Our study is based on the static models of Rayleigh, Potter, Frolich, and Preisach. Identification results show that the Preisach and Frolich static models can model the hysteresis curve of the Fe-3 wt%Si steel sheet more accurately than the other models studied.
Due to the need to reducing the cost of construction and minimizing the environmental impact in producing, a Doum palm fiber has been used as a reinforcement for plater mortar. The objective of this work is to study the mechanical properties of plater mortar reinforced with varying length and mass fraction of Doum palm fiber. However, naturel fiber have been affected by the Alkali environment of mortar, to avoid this problem an alkali treatment of fiber with sodium hydroxide solution of 1% concentration has been used in order to reduce the effect of alkali attack. In this framework, five-fiber contents (0.5%, 1%, 1.5%, 2%, and 2.5%) by weight and three types of fibers (powder fibers, mixture fibers, and long fibers) have been used. The experimental investigation depicts an improvement of flexural strength for a fibers content equal to 1% for powder fibers and mixture fibers and 0.5% for long fibers. This improvement is due to the alkali treatment which removes the impurities in the fibers. For compressive strength, for 2% of treated Doum Plam fiber, it increase about 4.41%, 9.57%, and 1.26% respectively for powder, mix, and long fibers. Only samples with treatment fibers show an enhanced flexural and compressive strength. Thus, the alkaline treatment is a suitable choice to avoid fiber degradation in the alkali environment.
- Dec 2017
Preisach model is widely used to characterize ferromagnetic material’s hysteresis. Thus, it is necessary to identify its parameters in order to complete magnetic hysteresis modeling successfully. In this paper, a stochastic identification method, Genetic algorithm, is implemented. The procedure consists of the minimization of the error between measurements and program results. Obtained results are compared with the classical nonlinear least square identification method and experimental hysteresis of a fully-process non oriented Fe-3 wt%Si steel sheet.
- Sep 2017
Magnetic properties of ferromagnetic materials are sensitive to mechanical deformation, temperature stress and frequency of excitation. This paper deals with the characterization of the behavior of ferromagnetic materials under plastic deformation. Our work attempts to take into account the plastic deformation in the analytical Jiles-Atherton model through its parameters: their variations with the mechanical deformation are deduced from an identification using genetic algorithm approach for each state of deformation. Sensitive parameters to the solicitation are extended to plastic deformation. Finally, simulation results are compared to experimental data of a fully process non oriented Fe-3. wt%Si steel sheet. The mean square error is less than 5% for each case which confirms the good agreement between simulated and measured hysteresis curves.
- Jul 2017
This work denotes an insight into an experimental and numerical investigation of adhesively bonded tubular specimens. A series of tensile tests have been conducted on joined E glass reinforced thermoset resins to study the effect of the resin nature on mechanical behaviour. It has been proved through experimental outcomes that E glass/Vinylester 411 resin tube presents the best tensile properties in comparison with others resins. Therefore, the mechanical behaviour of this specimen has been investigated under uniaxial loading. The damage mechanisms resulting from this experimental test have been identified by means of the X-ray tomography and scanning electron microscope. A numerical model has been undertaken in order to predict the mechanical behaviour and the damage propagation of adhesively bonded tubular specimens. It has been proved that experimental and numerical results are in perfect agreement.
- Jun 2016
- ECCM 2016 - Proceeding of the 17th European Conference on Composite Materials
The aim of this paper is the study experimentally and numericaly the mechanical behavior of E glass fiber/ Vinylester resin adhesively bonded tube using Araldite adhesive. The tensile tests have shown that, the mechanical behavior can be described by two phases. The first phase concerns the linaire elastic behavior. The second phase, is observed by a non lineaire behavior accompanied by the apparition and propagation of cracks in the bonding zone leading to the failure of the bonding interface. The damage mechanisms have been investigated thanks to scanning electron microscopy. In order to predict the mechanical behavior and the damage propagation of joined composite tube observed during the tensile tests, a numerical model is proposed. Mainly a good agreement between experimental and numerical results has been obtained.
During yarn formation by spinning, polyamide filaments are bent into approximately helical shapes and tension is created. Polyamide yarn undergone bending to compensate different stresses applied on filaments during the twist test. In this study, polyamide filaments of different linear density and circular cross-sectional shapes have been numerical simulated at different twist and tension levels. The twist behaviour of the multifilament has been simulated by using the ABAQUS finite element package and modelling the yarns as 3D continuum elements. The target of the research is to establish dependency relationships between certain factors (such as tension value, twist value and filament number) and the yarn bending expressed by the spatial orientation angle of the central filament. Statistical experiment design is used to optimize polyamide yarn bending phenomenon during spinning for a series of models varying in the tension value, twist value and filament number. Results indicate that the twist value and the yarn count are the most influential variables that control yarn bending. With a good choice of tension and twist values, yarn bending during spinning can be avoided.
The target of the research was to establish dependency relationships between certain factors (such as tension value, torsion value and filament number) and the yarn bending expressed by the orientation of the central filament spatial angle. Statistical experimental design was used to optimize yarn bending phenomenon during spinning for a series of models varying in the tension value, twist value and filament number. The twist behaviour of the multifilament was simulated using ABAQUS finite element package by modeling filaments as 3D continuum elements.
- Feb 2014
This paper presents an optimization of the mechanical properties of cement-Posidonia composite by means of experimental characterization. We are interested in producing composite of cement reinforced by Posidonia raw fibers. The ratio of fibers and water-to-cement mass is varied to determine its effect on the mechanical properties of the cement-Posidonia composite, particularly, its resistance to fracture. Three point bending and compression tests were carried out to study the mechanical properties of the composite. Scanning electron microscopy was used to examine the surface of the tested samples. The experimental investigation shows an improvement of flexural strength for a ratio W/C equal to 0.5 and fiber content equal to 10 vol%.
The twist angle is an important parameter of the yarn which determines the degree and shape of the filament’s deformation produced along their length. So, in this paper, a 3D numerical modelling of filaments assemblies has been developed. The twist behaviour of the multifilament was simulated using ABAQUS finite element package by modelling the yarns as 3D continuum elements. The distribution of filament helix angle according to the radial position of the yarn is evaluated. Results show that the helix angle draws near zero in the yarn axis but does not fall to zero in presence of migration, and becomes bigger as the filaments are positioned on the surface. Moreover, the twist angle is calculated for different twist level which proves that twist angle is highly affected by torsion level. The target of the research was to establish a relationship between twist angle, twist value and yarn linear density for a series of models varying in the filament radius, twist value and filament number.
Understanding the scratch behaviour of the composite materials is of primary importance. The scratch behaviour of glass fibre reinforced polyester composite was investigated. A new scratch device is designed and developed. Scratch tests at room temperature were carried out, using conical indenter and constant scratching velocity. The main aim of this study is to investigate the effects of tribological parameters on wear mechanisms and friction coefficient. Particularly, the effects of the normal load and the attack angle were presented. The different wear scenario of the composite material during the scratch test was deduced, then supported by an analysis of the glass fibre reinforced polyester composite wear modes using scanning electron microscopy (SEM) observations was performed. The correlation between tribological parameters and wear mechanisms was highlighted through the composite scratch map. Results were compared with those previously published associated with the metallic and the polymeric materials.
In this article a mechanical characterization of filament wound pipes is investigated. The tested pipes are composed of E glass/vinylester with ±55° angle wedding. The mechanical behavior under axial monotonic loading is studied using acoustic emission. The test was carried out according to the instructions of standard ASTM-D 2105-01 test. The experiment determines the damage mode using two methods: acoustic emission and tensile test. The results of acoustic emission associated to those obtained from tensile test, are very promising and show the relevance of the developed nondestructive test to the prediction of the mechanical behavior of filament wound pipes.
Résumé / Abstract : L’emploi des fibres végétales dans l’élaboration des matériaux composites est un secteur en plein expansion. On les utilise pour leur faible coût, leur disponibilité et leur reproductibilité. Les fibres utilisées dans cette étude sont extraites à partir des herbiers marins Posidonia Oceanica ; c’est une plante marine à fleurs avec des feuilles en forme de ruban. Cette plante présente un certain potentiel vu son intérêt écolo-gique et économique. Ce travail comporte une caractérisation mécanique des compo-sites polypropylènes renforcés de fibres de Posidonie à travers des essais de flexion 3 points. Ces composites ont été fabriqués en utilisant la méthode de moulage par injection. L’influence du taux de fibres sur les propriétés mécaniques du composite PP/Posidonie a été évalué et a montré que pour les différentes vitesses utilisées lors de l’essai de flexion (2, 10, 20 et 50mm/min), la contrainte maximale et l’allongement décroît avec l’augmentation du taux de fibres par contre on observe une aug-mentation du module en flexion des composites. Mots clefs : Polypropylène (PP), fibres de posidonie, composite, propriétés mécaniques.
The effect of chemical modification, reinforcement structure and fiber weight ratio on the flexural proprieties of Luffa-polyester composites was studied. A unsaturated polyester matrix reinforced with a mat of Luffa external wall fibers (ComLEMat), a short Luffa external wall fibers(ComLEBC) and a short Luffa core fi-bers (ComLCBC) was fabricated under various conditions of fibers treatments (combined process, acetylat-ing and cyanoethylating) and fiber weight ratio. It resorts that acetylating and cyanoethylating enhance the flexural strength and the flexural modulus. The fiber weight ratio influenced the flexural properties of com-posites. Indeed, a maximum value of strength and strain is observed over a 10% fiber weight ratio. The uses of various reinforcement structures were investigated. The enhancement of elongation at break and the strain values of the composite reinforced by natural mat was proved.
Effects of surface chemical modifications of luffa fibers on mechanical and hygrothermal behaviors of polyester/luffa composites were studied. Unsaturated polyester resin was used as matrix. Untreated, alkali-treated, treated with combined process, and acetylated luffa fibers were used. Scanning electron microscopy and infrared spectroscopy were used to characterize the morphology and chemical structure of the luffa fibers. The mechanical properties of the composites were characterized using the three-point flexural bending test. Water absorption tests were conducted on both the fibers and the composite materials by immersion in distilled water at 25°C. The acetylation treatment improved the mechanical properties. As shown by infrared analysis, the process decreased the hydrophilic behaviour of the luffa fibers, improving their adhesion to the polyester matrix. The chemical modifications at the surface of the luffa fibers also decreased the diffusion coefficient and the maximum amount of water absorbed by these fibers. Moreover, it was observed that for the fibers tested in this study, the diffusion process was "Fickian "at earlier times of immersion, but became complicated towards the end of the immersion. Similar results have been obtained for composite materials at earlier stages of water immersion. The diffusion process was found to be affected by external loads applied on the exposed composite materials. As the load increased, the amount of absorbed water increased at a higher rate of diffusion.
Acoustic emission is one of the most innovative of non-destructive testing techniques because makes it possible to follow in real time the damage of composite materials. The aim of this paper is to study the effect of variation in the resin type on the mechanical behavior and the acoustic activity of the filament wound pipe under monotonous axial loading. The results obtained show that the mechanical behavior as well as the acoustic activity of the filament wound pipe change for each type of studied resin.
A three dimensional (3D) numerical model of filaments assemblies has been developed in this paper. The twist behaviour of the multifilament is simulated by using the ABAQUS finite element package and modelling the yarns as 3D continuum elements. This study describes the phenomenon of migration with different levels of twist and tension. The filament trajectory has been visualised for yarn made of a 3 layered structure (external, internal and central) of 19 filaments to show the existence of the migration phenomenon. Furthermore, a study of the mean filament position is evaluated for all filaments in the yarn. The twisting tension and twist values appear to be the most influential variables that control filament migration in twisted yarns.
- May 2011
A three dimensional (3D) numerical modelling of filament assemblies has been developed in this study. The twist behaviour of the multifilament is simulated using the ABAQUS finite element package by modelling the yarns as 3D continuum elements. The migration of the filaments has been shown in a previous paper. In this study, we will describe a quantitative analysis of filament migration for different levels of twisting tension and torsion. The distribution of the filament orientation angle in accordance to the radial position and the axial position of the yarn are evaluated.
Résumé : Le palmier doum appartient à la famille des monocotylédones, c’est un arbre abondant en Tunisie. Son utilisation était limitée dans les secteurs agricole et artisanal. Afin de pouvoir élargir le domaine d’exploitation de cette ressource fibreuse, une caractérisation détaillée des fibres du palmier doum a été déjà étudiée. Une élaboration du composite biodégradable a été menée par un plan factoriel complet afin de savoir les conditions optimales pour obtenir les meilleurs propriétés mécaniques. Notre étude est focalisée à l’analyse du comportement mécanique suivi par des essais de flexion trois points du composite biodégradable obtenu à partir des pétioles du palmier doum. Mots clés : fibres du palmier doum/ composite biodégradable / thermo compression/ propriétés mécaniques
A 3D numerical modelling of filaments assemblies has been developed. The twist behaviour of the multifilament was simulated using ABAQUS finite element package by modelling the yarns as 3D continuum elements. The distribution of filament helix angle according to the radial position of the yarn is evaluated. Results show that the helix angle draws near zero in the yarn axis but not fall to zero with presence of migration, and become bigger as the filaments are positioned at surface. The aim of the research was to establish the relationship between twist angle, torsion value and yarn linear density for a series of models varying in the filament radius, twist and filament number.
The effect of chemical modification, reinforcement structure and fibre weight ratio on the flexural proprieties of Luffa-polyester composites was studied. A unsaturated polyester matrix reinforced with a mat of Luffa external wall fibres (ComLEMat), a short Luffa external wall fibres(ComLEBC) and a short Luffa core fibres (ComLCBC) was prepared under various conditions of fibres treatments (combined process, acetylating and cyanoethylating) and fibre weight ratio. It resorts that acetylating and cyanoethylating enhance the flexural strength and the flexural modulus. The fibre weight ratio influences the flexural proprieties of composites. A maximum value of strength and strain is observed over a 10% fibre weight ratio. The strain values of different composites show a rise when we use a Luffa mat as a reinforcement structure.
Yarn twist in spun yarns has the primary function of causing constraints and compressive stresses to be generated. It will be convenient, in the present paper, to study the contact and inner pressure in a twisted yarn. The twist behavior of the multifilament was simulated using ABAQUS finite element package by modelling the yarns as 3D continuum elements. The results of this analysis showed highest level of contact pressure in the yarn surface that decreases while leading to the center as well as for the inner pressure and revealed the existence of migration in the twisted yarn. Moreover, the distribution of the inner pressure according to the radial position showed the presence of compressed and swollen zones in the twisted yarn.
Yarn twist in spun yarns has the primary function of causing constraints and compressive stresses to be generated. It will be convenient, in the present study, to study the contact and inner pressure in a twisted yarn. The twist behavior of the multifilament was simulated using ABAQUS finite element package by modelling the yarns as 3D continuum elements. The study was conducted on the simulation of a 19 polypropylene filaments assembly with a circular cross section. Factors, such as dimensions and properties of filaments and interactions between filaments are included in the model. To simulate the torsion filament assembly was embedded from one side and twisted from the other. There after, we investigated the inner and contact pressure of all existing filaments inside the yarn. The results of this analysis showed highest level of contact pressure in the yarn surface that decreases while leading to the center as well as for the inner pressure and revealed the existence of migration in the twisted yarn. Moreover, the distribution of the inner pressure according to the radial position showed the presence of compressed and swollen zones in the twisted yarn.
RESUME : Dans ce papier, nous proposons une méthode pour la caractérisation du comportement mécanique des joints soudés par induction à haute fréquence pour des tubes ronds en acier doux S235JR. Cette technique de caractérisation est basée sur la réponse à la traction simple des éprouvettes comportant le cordon de soudure, sur des mesures de microdureté et sur la règle des mélanges. Les paramètres du comportement du cordon de soudure et de la zone affectée thermiquement sont obtenus en identifiant la réponse expérimentale de l'essai de traction simple de l'éprouvette soudée à l'expression du modèle d'écrouissage calculé par la règle des mélanges. La simulation numérique par éléments finis permet d'évaluer la pertinence de l'approche proposée et de valider les hypothèses admises pour cette méthode. Les résultats numériques et expérimentaux sont alors comparés. Les résultats obtenus montrent l'utilité et la performance de cette méthode pour déterminer le comportement plastique des tubes soudés. INTRODUCTION : La mise en forme des tubes métalliques par déformation plastique est largement répandue dans l'industrie automobile et aéronautique (Aue-U-Lan, 2004). La possibilité de fabriquer des composants de géométrie complexe, de faible coût, de faible poids et de forte rigidité, pousse les industriels à s'investir dans la recherche de maîtriser des procédés de transformation des tubes. La majorité des tubes déformés que ce soit par hydroformage, par cintrage, ou par autres procédés sont des tubes soudés. Les tubes soudés en acier représentent actuellement le deux tiers de la production mondiale des tubes (Hashmi, 2006). Le cordon de soudure ou la Zone Fondue (ZF) et la Zone Affectée Thermiquement (ZAT) présentent des caractéristiques mécaniques différentes de celles du matériau de base dû à des modifications métallurgiques locales
Résumé : vu leur intérêt écologique, et économiques, les fibres végétales font l’objet de plusieurs travaux de recherches afin de les utiliser comme renfort dans des matériaux composites. Parmi ces fibres on cite la posidonie. La Posidonie est une plante sous marine qui se trouve sous forme de feuilles et de pelotes (fig.1); ces dernières sont des agglomérats de fibres. Cette plante présente un certain potentiel, d'où l'intérêt de l'exploiter. Afin de valider l'utilisation de cette plante, on s’est intéressé à la réalisation d’un composite ciment renforcé par des feuilles et des fibres de posidonie brutes. Des essais de flexion 3 points ont été réalisés afin de caractériser mécaniquement ces composites. Les résultats obtenus ont montré une amélioration de la résistance à la flexion pour un rapport eau/ciment=0.6 pour un taux de renfort de 15%; par contre, on observe une régression de la résistance à la flexion pour un rapport eau/ciment=1. Mots clés : ciment, fibres et feuilles de posidonie, propriétés mécaniques
Résumé : Le palmier doum appartient à la famille des monocotylédones, c’est un arbre abondant en Tunisie. Son utilisation était limitée dans les secteurs agricole et artisanal. Afin de pouvoir élargir le domaine d’exploitation de cette ressource fibreuse, une caractérisation détaillée des fibres du palmier doum a été menée. L’inconvénient majeur pour ces composites à base des fibres naturelles est la sensibilité aux conditions environnementales, telles que la température et surtout la présence de l’humidité. Il est alors impératif d’étudier l’évolution des propriétés mécaniques vis-à-vis de l’absorption de l’eau au cours du temps. Dans ce travail, La diffusion d’eau dans le composite polyester insaturé /fibres du palmier doum est analysée expérimentalement par détermination des cinétiques d’absorption sous immersion dans l’eau distillée. Ceci pour le composite renforcé par des fibres continues, mats et courtes ; tout en variant le pourcentage massique des fibres de 5% à15% et la température d’immersion : 25°C, 50°C et 80°C. Les propriétés mécaniques en fonction de la quantité d’eau absorbée sont mises en évidence et quantifiées lors d’essais expérimentaux de flexion trois points avant et après immersion de tous les types des composites étudiés. Mots clés : Fibres du palmier doum, vieillissement, propriétés mécaniques.
Résumé: Ce papier se focalise sur les propriétés physiques et mécaniques des ciments renforcés par des fibres. C’est un secteur en plein essor et d’après les travaux de recherche plusieurs avantages sont constatés. Dans cette étude expérimentale, on a varié la fraction volumique des fibres afin de déterminer son effet sur les propriétés de la rupture et la résistance à la flexion des composites ciment-posidonie. La fibre est caractérisée par observation microscopique, par la masse volumique et aussi par spectroscopie infrarouge. Les propriétés mécaniques du composite sont étudiées en réalisant des essais de flexion trois points. Les résultats obtenus montrent une amélioration jusqu’à un taux volumique de 20% de fibres dans le mélange puis une régression est observée. Mots clés : ciment, fibres de posidonie, propriétés physiques, propriétés mécaniques.
Résumé: L'absorption d'eau dans les composites à matrice polymère renforcée par des fibres naturelles est un souci sérieux particulièrement dans les zones humides. Dans cette étude, Les composites à matrice polyester insaturé renforcés par les fibres continues du palmier doum avec un taux massique des fibres (10% et 14%) et à température (ambiante et 50°C), sont soumis au vieillissement en immersion dans l’eau distillée. La diffusion de l’eau dans ces composites est fickienne, le taux d’absorption évolue avec l’augmentation du taux des fibres et le coefficient de diffusion accroit avec la température. L’effet du traitement alcalin des fibres sur la cinétique d’absorption a été étudié. Il engendre une diminution du taux d’absorption et un ralentissement de la diffusion. Mots clés : fibres naturelles, absorption, vieillissement
Natural fibers as an alternative fiber reinforcement material have significant advantages over glass. Indeed, they are more environmentally friendly, healthier and safer. Their application in polymer composites requires the understanding of their structure and mechanical properties. Other advantages of using the cellulose fibers as reinforcement are their low densities and their non-abrasive aspect. Various natural fibers have been widely used. Others, however, remain of limited use such as in the case of palms. This study aimed at introducing palm fibers to be used as reinforcement in a polymeric matrix enabling production of economical and lightweight composites for load-carrying structures. First, an investigation of the extraction procedures of fibers from folioles and leafstalks of doum palm was undertaken. Secondly, the mechanical behavior of the treated and untreated doum palm fibers was studied to determine their mechanical properties. Finally, we compared the mechanical properties of the different parts of the tree with other natural fibers.
Résumé Dans cette étude une analyse de l’influence du traitement sur les propriétés mécaniques du composite palmier doum/ polyester orthophtalique a été détaillée. Le traitement alcalin améliore les propriétés mécaniques des fibres ultimes du palmier doum, élimine leurs impuretés résiduelles et influe sur les propriétés mécaniques du composite. Ce papier présente les résultats d'une étude expérimentale pour inculquer les caractéristiques mécaniques du composite à fibres longues unidirectionnelles et fibres courtes polyester orthophtalique / fibres du palmier doum. Mots clefs : Fibres naturelles, palmier doum, traitement alcalin, propriétés mécaniques.
- Mar 2009
- Colloque Franco-Maghrebin “Membranes et films composites” (CFMMFC09) ; 26th to 28th March 2009
- Feb 2009
In the presents study, an analysis of the influence of alkaline treatment for different concentrations as well as that of the enzymatic treatment on the morphology and on the mechanical properties of the leafstalk doum palm fibres is detailed to improve the hydrophobicity, the compatibility fibre/matrix and the composite mechanical resistance. The fibre surface topography has been characterized by SEM. And the obtained images show that the alkaline treatment gives porous fibres and the biological treatment gives smooth surfaces. The results confirm that both treatments eliminate the fibre residual impurities and influence their properties. A tensile test series were carried out to study the effect of the treatments on the mechanical features of the leafstalk doum palm fibres. The chemical treatment for a concentration of 1.5 N has improved considerably the mechanical properties. The composites used were made of doum palm fibres as reinforcement for epoxy resins. The composite mechanical properties have been studied from flexural tests. This study presents the results of an experimental investigation in order to select the best mechanical characteristics of epoxy resin/doum palm fibres.
Recently, the use of lignocellulosic fibres to reinforcing composite has received an increased attention. However, lack of good interfacial adhesion makes important the treatment of raw materials. Chemical treatment prepared the raw material to be useful by elimination of gummy and waxy substances. In this study, the Luffa fibres were treated by tow methods: alkali treatment and mixed treatment (sodium hydroxide and hydrogen peroxide). The effect of these treatments on the structure of fibres was showed using SEM and XRD (X-Ray Diffraction) analysis. The SEM results revealed that both treatments resulted in a removal of lignin, pectin and hemicellulose substances, and change the characteristics of the surface topography. The XRD analysis shows the increase of crystallinity index by many treatment conditions. We find that the alkali treatment (120 °C; 3 h; 4% NaOH) shows a good cleaning and the higher crystallinity index of treated fibres. It is also interesting to note that mixed treatment can change the Luffa fibres from mat structure to fibrils structure.
- Dec 2008
The transport of granular material often generates severe damage. Understanding the correlation between the friction coefficient, particle geometry and wear mechanisms is of primary importance for materials undergoing abrasive wear. The aim of this study is to investigate the effect of particle geometry on wear mechanisms and the friction coefficient. Numerical and analytical simulations and experimental results were compared. The process to be studied is the scratch made by a rigid cone with different attack angles on a 5xxx aluminium alloy (Al–Mg) flat surface. A scratch test was used and the wear mechanisms were observed for different attack angles. A numerical study with a finite element code was made in order to understand the effect of attack angles on the friction coefficient. Two numerical models with and without damage have been developed. The contact surface and the friction coefficient were studied too, and the results compared to the Bowden and Tabor model. The superposition of the numerical, analytical and experimental results showed a better correlation between the wear mechanisms and the friction coefficient. It also showed the importance of the model hypothesis used to simulate the scratch phenomenon.
The Luffa sponge, fruit of Luffa cylindrical, is one of the vegetable resources which can be used in such technical applications. In this study, we investigate the effect of chemical treatment of Luffa fibres in the flexural properties of polyester-Luffa composites. We confirm that the treatment of acetylation improves the flexural properties of the reinforced polyester composite. It is also showed that the increase in the weight fraction of reinforcement improves the behaviour of composite materials. The flexural strength and flexural modulus reached respectively 46,6 Mpa and 2,03 Gpa for PES/Luffa acetylated with weight fraction of 9%.
This study deals with the filament migration into the yarn assembly by using a 3D numerical modelling. The twist angles of filaments belong to the outer, inner and central layer for different levels of torsion is measured and analyzed for two variety of yarn: the first composed of 19 filaments. At the same time, a study of migration parameters and spatial orientation angle are evaluated to show the existence of migration phenomenon for all filaments in a yarn.
A 3D numerical modelling of filaments assemblies has been developed. The twist behaviour of the multifilament was analysed using finite element analysis by modelling the yarns as 3D continuum elements. This study describes the phenomenon of migration with different levels of twist and tension. The filament trajectory has been visualised for different layer (external, internal and central). The results may provide a foundation for further study of twist angle for different layer of yarn with varied value of twist and tension.
In this article, the distribution through the thickness of both the matrix's modulus and the interfacial shear strength (IFSS) in dry and aged pultruded polyester/glass fiber composites containing fillers and low profile additives are experimentally evaluated, using the nanoindentation test. The obtained results indicate that for the dry composite, both the matrix's modulus and the IFSS are constant across the thickness of that material. As a consequence of the immersion in distilled water at high temperature (65°C), the IFSS was found to exhibit a parabolic trend through the thickness of the aged specimen, with the lowest value at the external surfaces. Such minimum was reached after a short time of immersion. At the saturation time, the IFSS at all layers of the aged specimen reaches lowest value. This was not the case for the matrix's modulus, since the later was found to be not affected by the amount of the absorbed humidity. Similar results were obtained after immersion in sea water at the same temperature. However, the only difference noted was at the external surface of the aged specimen where additional degradation had taken place in the matrix and at the fiber/matrix interface. This was attributed to the accumulation of a large amount of salt molecules at the external surface of the aged specimen during the exposure process. Additional mechanical tests show that after 120 days immersion in hot water the interlaminar shear strength of the material as measured according to the ASTM standard D2344, is reduced by 35%. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers
Purpose – The purpose of this paper is to study the correlation between abrasive wear resistance, contact configuration and grain size of aluminium alloy. Design/methodology/approach – Different aluminium alloy with different grain size has been tested using a scratch test. Comparison between scratch parameters, especially scratch depth and grain size aluminium alloy, has been made. Two indenters were used: conical and spherical indenter. Findings – Correlation between grain size of aluminium alloy, configuration contact and abrasive wear resistance has been discussed. This study can be useful for choosing material which can provide better abrasive wear resistance. Originality/value – This study can be a reference both practically and academically. A similar study has been made in order to investigate the effect of hardness in abrasive wear resistance. However, the importance of microstructure and especially the grain size of aluminium alloy have been taken into account.
The interest in using natural fibres in composites has increased in recent years thanks to their light weight, non-abrasive, combustible, non-toxic, low cost and biodegradable properties. However, lack of good interfacial adhesion and poor resistance to moisture absorption make the use of natural fibre reinforced composites less attractive. Chemical treatment of the fibre eliminated gummy and waxy substances from the fibre surface, modified the surface, reduced the moisture absorption and increased the surface roughness. In this study, luffa ecorse fibres (LE) were pre-treated with mixed process containing sodium hydroxide and hydrogen peroxide. The pre-treated fibres were modified using chemical treatments such as acetylation (Ac), cyanoethylation (Cya) with different concentrations and grafting acrylic acid (AA). The treatment effects on the fibres have been characterized by means of infrared spectroscopy and water absorbency. It was found that treatments reduced the overall water uptake of Luffa ecorse fibres and enhance their interfacial adhesion when they are used in composites materials. Introduction A combination of properties of some natural fibres, such as low cost, low density, non-toxicity, high specific properties, no abrasion during processing, and recycleability, contribute to a rising interest from the manufacturing industry of low cost, low weight composites. Despite the advantages of cellulosic fibres in thermoplastics, the polymer-cellulose composites materials is handicapped by their low permissible processing temperatures and highly hydrophilic character associated with a low compatibility of hydrophobic polymers as well as with a loss of mechanical proprieties after moisture uptake [1, 2]. Due to the poor compatibility, surface of fibres most be treated to improve the interface between fibre and matrices. Beldzki et al  reported many methods to modify the surface of natural fibres for their use in composite materials. A.K. Saha et al [3, 4, and 7] modified jute fibre with acrylonitrile to reduce the absorption of fibres. They reports also that when the duration of reaction and the rate of acrylonitrile in solution increase the cyanoethylation ratio. Many searchers [5, 6, 8] reported that the treatment of cellulose based fibres with acetic anhydride decrease their hydrophilic behaviour by the substitution of hydroxyl groups by acetyl groups. Others searchers reported that chemical modification of fibre surface enhance the mechanical proprieties of composites materials. The Luffa cylindrica has a ligneous fibrous netting system in which the fibrous cords are disposed in a multidirectional array, forming a natural mat. Gianpitro  has reported that the fibres which are composed of 60% cellulose, 30% hemi cellulose and 10% lignin. BOYNORD et al  assumed that using Luffa fibres in composite material may be very advantageous. In the present work, the pre-treated Luffa ecorse fibres were treated with acrylonitrile, acetic anhydride and acrylic acid. Untreated, pre-treated and modified fibres were characterized using infrared spectroscopy and surface energy. The absorption capacity and retention of water were also evaluated in order to prove the surface modification efficiency.
Today the scratch test is an important tool, widely used for the development of some industrial sectors (anti-scratch coating, glass industries, automobile industries,...). Surface mechanics uses this process to characterise the local and interfacial behaviour of material (wear, friction and adherence). In this work, an aluminium alloy, used for the transportation of a granular material, is studied. A comparison of experimental, numerical and analytical results is discussed. (c) 2007 Elsevier B.V All rights reserved.
Nous présentons, dans ce travail, une modélisation de l'essai de torsion d'un assemblage de filaments en polypropylène de section creuse. Nous nous intéressons à l'étude du phénomène de pression, voire la pression interne et la pression de contact entre les filaments. L'identification du comportement viscoélastique est effectuée à partir des essais de traction et de relaxation. La simulation de la torsion des textiles linéaires a été réalisée avec le code de calcul par éléments finis ABAQUS qui permet de résoudre des problèmes allant des analyses linéaires relativement simples aux simulations non linéaires les plus compliquées.
- Nov 2006
- Cinquièmes Journées Scientifiques et techniques en Mécanique et Matériaux JSTMM’06
The aim of this study is to give scientific data about the physical, morphological and mechanical proprieties of esparto fibres. The use of esparto fibres for reinforcing thermoplastics is a novel way. That is why a better investigation of their proprieties and surface characteristics is necessary to maximize their potential use. In this study, different methods of extraction were conducted on the fibres using mechanical separation (At1), aqueous solution of NaOH 3N (At2) and chemical modification by acetylation (At3). Esparto fibres were characterized through technical analysis such as SEM and FTIR. The result of microscopic analysis shows that esparto fibres have a similar structure to that of a composite material in which the ultimate fibres of cellulose constitute the reinforcement. The pycnometric measurement shows that the density of esparto fibres is similar to those of jute and Agave americana L. The FTIR spectra of various esparto fibres show a decrease of the number of carboxyl groups after (At2) fibres acetylating. This result proves the contribution of the chemical modifications for the hydrophobic improvement of the proprieties of fibres. In addition a comparison between properties of esparto fibres and other vegetal ones has been integrated. The results of this study indicate that technical esparto fibres can have promising properties especially in reinforcement of composite materials
The transport of granular material often generates severe damage. Understanding the correlation between the friction coefficient, particle geometry and wear mechanisms is of primary importance for materials undergoing abrasive wear. The aim of this study is to investigate the effect of particle geometry on wear mechanisms and the friction coefficient. Numerical and analytical simulations and experimental results have been compared. The process to be studied is the scratch made by a rigid cone with different attack angles on a 5xxx aluminium alloy (Al–Mg) flat surface. A scratch test was used and the wear mechanisms were observed for different attack angles. A numerical study with a finite element code was made in order to understand the effect of attack angle on the friction coefficient. The contact surface and the friction coefficient were also studied, and the results compared to the Bowden and Tabor model. The superposition of the numerical, analytical and experimental results showed a better correlation between the wear mechanisms and the friction coefficient. It also showed the importance of the model hypothesis used to simulate the scratch phenomenon. To cite this article: S. Mezlini et al., C. R. Mecanique 333 (2005).
- Feb 2001
An analytical shear-lag model has been developed for quantifying the interfacial shear strength of glass-reinforced composites from micro-indentation experiments. The model takes into account the local fibre environment, together with the occurrence of debonding and fibre sliding. In order to simulate the experimental indentation curves, various interfacial laws have been implemented. In a first approach, it was assumed that the shear stress in the debonded part of the interface was constant and proportional to the debonding stress. A more refined generalised interface law relating the shear stress to the fibre displacement was subsequently introduced to describe a progressive transition from an adhesive to a sliding state. The model has been successfully applied to the analysis of experimental reduced indentation curves giving the displacement of the fibre surface as a function of the applied load.
- Feb 2000
A shear-lag model has been developed in order to assess interfacial shear strength from micro-indentation experiments. The treatment of the experimental load/displacement curves is based upon the quantification of the two components of the indenter displacement, i.e. (i) the elasto-plastic indentation of the fibre surface by the Vickers indenter, and (ii) the displacement of the fibre surface due to its compression and to the deflection of the matrix. The latter component has been modelled by using an analytical shear-lag model which takes into account both fibre/matrix debonding and fibre sliding in the debonded areas. Some of the basic hypothesis of this analytical approach have been checked by finite-element (FE) simulations with appropriate model configurations. By means of this model, the critical shear debonding stress can be obtained from the experimental indentation curves. Moreover, the data-reduction scheme takes into account separately the local environment of each indented fibre. This method has been successfully applied to experimental data by using a unidirectional E-glass/epoxy composite.
- Jan 1999
- GAMM annual meeting
A mono-dimensional shear lag model has been developed in order to assess the interfacial shear strength from microindentation test. The treatment of the experimental load/displacement curves is based upon the quantification of the two components of the indenter displacement (the elasto-platic indentation of the fibre surface by the Vickers indenter and the displacement of the fibre surface due to the elastic stifness of fibre-matrix system together the interface sliding). The developed model was used for a quantitative analysis of the experimental indentation curves obtained on a variety of composite materials. Some extensions of the model are developed to account for some deviations between the model and the experiments.
- Jan 1999
The aim of this study was to evaluate the effect of post curing by heat of the mechanical properties of woven glass-polyester composites. A three point bending test was considered under monotonic static and repetitive cyclic loadings. The damage mechanisms of specimen cross section were analysed using an optical microscope. Upon the post curing by heat it was confirmed that the mechanical properties of the woven glass-polyester composites were increased moderately and the cure performance of the composite was also improved. Micro indentation tests were applied to study the quality of fibre-matrix interface by using both post cured and non post-cured. composites. The results of micro-indentation tests were in agreement with the monotonic and fatigue test and confirmed that post-cure improves the resistance of fibre-matrix interface.
Le rôle de l' interface fibre-matrice dans le comportement mécanique, la tenue en fatigue et la durabilité des composites est largement établi. Le développement de techniques de caractérisation fiables des propriétés mécaniques de l' interface est à cet égard déterminante et a justifié le développement d'une panoplie d'essais micromécaniques. Parmi ceux-ci, l'essai de microindentation instrumentée présente l'intérêt de pouvoir être mis en oeuvre sur des composites réels et donc sur des interfaces réelles. Le traitement des courbes de microindentation est basé sur la dissociation du déplacement de l'indenteur en deux composantes. La première composante correspond à l' indentation élastoplastique de la surface de la fibre par l'indenteur Vickers. Cette composante d' indentation est mise en évidence par l'empreinte rémanente laissée par l' indenteur sur la surface de la fibre après indentation. La deuxième composante (courbe d' indentation réduite) correspond au déplacement de la surface de la fibre dû à la compression de la fibre et au cisaillement de la matrice. La détermination des paramètres du modèle se fait par identification sur la totalité de la courbe de mise en charge. A cet effet, une procédure de calcul par minimisation de la variance a été implémentée sur le logiciel de traitement de la machine.
- Nov 1996
The indentation technique has been developed to perform surface mechanical characterization of materials. This technique consists in monitoring the penetration of a diamond indenter in the material to be characterized while the displacement and the force are continuously measured. Modelling loading and unloading curves allows estimation of plastic and elastic properties of the material. Linking this technique with an optical sighting system permits the characterization of various phases of the composite materials with a displacement accuracy better than 0·1 μm. The mechanical behaviour of carbon or glass fibre reinforced polymer under various solicitations is mainly related to the behaviour of its ‘phases’: the matrix, the fibres and the fibre–matrix interface. Several techniques have been developed giving information about mechanical properties of the composite, particularly for the interfacial strength. Modelling static and dynamic indentation curves on fibres allows computation of the interfacial strength and fibre mechanical properties.This paper presents our indentation technique and the model that we have developed to study glass fibre–epoxy matrix and carbon fibre–epoxy matrix composites with a fibre diameter of 5–20 μm.