[pt] Este trabalho discute experimentalmente a utilização de fibras naturais em compósitos cimentícios para o reforço de elementos estruturais de concreto. Para tal, foram analisadas a morfologia e a durabilidade de fibras de curauá, cânhamo e sisal, bem como suas propriedades mecânicas. Dentre as fibras estudadas, o curauá apresentou o melhor desempenho, o que justificou sua implementação como reforço nos compósitos cimentícios. Para o projeto do compósito, foi decidido que o volume de fibras seria aplicado dividido em três camadas paralelas, em um arranjo alinhado longitudinalmente, como um tecido unidirecional. Os compósitos cimentícios reforçados com tecido de curauá foram mecanicamente caracterizados por testes de tração, flexão, compressão e cisalhamento. Após a investigação no nível material, o compósito desenvolvido foi aplicado sobre a superfície das vigas estruturais como um laminado afim de aumentar a capacidade portante sob duas condições de carregamento: flexão e cisalhamento. Os resultados experimentais dos ensaios estruturais foram confrontados com modelos analíticos para comparação. Os compósitos apresentaram um comportamento mecânico de alta performance, tendo alcançado o comportamento strain-hardening em todos os casos. Como reforço estrutural, o compósito proporcionou às vigas aumentos de resistência e ductilidade. Foi observado também um atraso no escoamento dos vergalhões de aço. / [en] This work experimentally discusses the use of natural fibers in cement-based composites for the strengthening of concrete structural elements. For such, the morphology and durability of curauá, hemp, and sisal fibers were analyzed, as well as their mechanical properties. Among the studied fibers, the curauá presented the best performance, which justified its implementation as reinforcement for cement-based composites. For the composite design, it was decided that the volume of fibers would be applied splitted into three parallel layers, in a longitudinally aligned arrangement, like a unidirectional fabric. A layer of this fabric was performed under a tensile test aiming to better understand its mechanical behavior. The cement-based composites reinforced with curauá fabric were mechanically characterized by tensile, bending, combined load compression, and shear tests. After the investigation at the material level, the developed composite was applied over the surface of structural beams as laminates, seeking to provide its strengthening under two distinct loading conditions: bending and shear. The experimental results of the structural tests were confronted with analytical models for comparison. The composites showed a high mechanical performance, achieving the strain-hardening behavior in all cases. When used as a structural reinforcement, the composite provided to the beams increases of strength and ductility. It was also observed a yielding delay in the steel reabars.

No description available.

Miniature compliant grippers are designed and developed to manipulate biological cells and characterize them. Apart from grippers, other compliant mechanisms are also demonstrated to be effective in manipulation and characterization. Although scalability and force-sensing capability are inherent to a compliant mechanism, it is important to design a compliant mechanism for a given application. Two techniques based on Spring-lever models and kinetoelastostatic maps are developed and used for designing compliant devices. The kinetoelastostatic maps-based technique is a novel approach in designing a mechanism of a given topology and shape. It is also demonstrated that these techniques can be used to tune the stiffness of a mechanism for a given application. In situations where any single mechanism is incapable of executing a specific task, two or more mechanisms are combined into a single continuum with enhanced functionality. This has led to designs of composite compliant mechanisms. Biological cells are manipulated using compliant grippers in order to study their mechanical responses. Biological cells whose size varies from 1 mm (a large zebrafish embryo) to 10 µm (human liver cells), and which require the grippers to resolve forces ranging from 1 mN (zebrafish embryo) to 10 nN (human cells), are manipulated. In addition to biological cells, in some special cases such as tissue-cutting and cement-testing, inanimate specimens are used to highlight specific features of compliant mechanisms. Two extreme cases of manipulation are carried out to demonstrate the efficacy of the design techniques. They are: (i) breaking a stiff cement specimen of stiffness 250 kN/m (ii) gentle grasping of a soft zebrafish embryo of stiffness 10 N/m. Apart from manipulation, wherever it is viable, the mechanisms are interfaced with a haptic device such that the user’s experience of manipulation is enriched with force feedback. An auxiliary study on the characterization of cells is carried out using a micro¬pipette based aspiration technique. Using this technique, cells existing in different conditions such as perfusion, therapeutic medicines, etc., are mechanically characterized. This study is to qualitatively compare aspiration-based techniques with compliant gripper-based manipulation techniques. A compliant gripper-based manipulation technique is beneficial in estimating the bulk stiffness of the cells and can be extended to estimate the distribution of Young’s modulus in the interior. This estimation is carried out by solving an inverse problem. A previously reported scheme to solve over specified boundary conditions of an elastic object—in this case a cell—is improved, and the improved scheme is validated with the help of macro-scale specimens.

Si l'emploi des matériaux composites dans l'aéronautique est déjà effectif sur des éléments de structures principales et de grande taille, leur généralisation aux structures secondaires bute sur leur positionnement en termes de coûts et performances face aux métaux. Il s'agit dans ce travail de contribuer à la mise en place d'une filière française de pièces composites hautes performances à bas coûts en s'appuyant sur un procédé de moulage en grande série, à savoir le thermoformage à haute pression. Ainsi, il a été question dans un premier temps d'optimiser ce procédé vis-à-vis des principales matières rencontrées dans les structures aéronautiques. Ensuite, les stratifiés moulés ont été caractérisés et les effets des conditions environnementales sévères (humidité, température, impact) sur leur comportement mécanique étudiés. Par ailleurs, réduire les coûts des pièces signifie également réduire les coefficients de sécurité qui restent très élevés pour les pièces composites. Cela passe par une meilleure prédictibilité de la rupture des matériaux et du comportement mécanique au-delà du linéaire. Sur le carbone/PEEK satin de 5 pris comme matériau d'illustration, les phénomènes non linéaires (viscoplasticité) ainsi que les mécanismes d'endommagement et de rupture ont été étudiés. Un accent particulier a été mis sur le délaminage et un critère permettant de prédire son amorçage a été proposé. La possibilité de faire des modèles éléments finis des pièces directement à l'échelle mésoscopique (du pli) a été également explorée et laisse entrevoir des pistes prometteuses pour des dimensionnements plus sûrs et donc moins conservatifs. / If the use of composite materials is already effective on elements of main structures and large size parts, their generalization to secondary parts is not effective due to their cost and their performances compared to metals. The framework of this thesis is to contribute to the establishment of a French chain of high performance composite parts at low cost. Thus, it was initially question of optimizing the process vis-à-vis the main composite materials used in the aerospace structures. Then, the molded laminates were characterized and the effects of severe conditions (humidity, temperature, impact) on their mechanical behavior were studied. Also, reduce the cost of parts also means reducing the safety factors which remain very high. This requires a better prediction of the failure and the mechanical behavior beyond the linear. Taking the five harness satin weave carbon/PEEK material as example, non-linear phenomena (viscoplasticity), damage mechanisms and failure criteria were studied, with particular emphasis on the delamination. The possibility to perform finite element analysis of the parts directly at the mesoscopic scale (ply-scale) was also explored and suggests promising expectations for a less conservative sizing of composite structures.

Uma grande diversidade de macrofibras poliméricas para reforço de concreto se encontram disponibilizadas hoje em dia. Por natureza estas fibras apresentam grande diversidade de características e propriedades. Estas variações afetam sua atuação como reforço no concreto. No entanto, não há normas brasileiras sobre o assunto e as metodologias de caracterização de normas estrangeiras apresentam divergências. Algumas normas definem que a caracterização do comportamento mecânico deva ser feita nos fios originais e outras que se devam utilizar métodos definidos para caracterização de materiais metálicos. A norma EN14889-2:2006 apresenta maior abrangência, mas deixa dúvidas quanto à adequação dos critérios de caracterização geométrica das fibras e não define um método de ensaio específico para sua caracterização mecânica. Assim, há a necessidade de estabelecimento de uma metodologia que permita a realização de um programa de controle de qualidade da fibra nas condições de emprego. Esta metodologia também proporcionaria uma forma de caracterização do material para estudos experimentais, o que permitiria maior fundamentação científica desses trabalhos que, frequentemente, fundamentam-se apenas em dados dos fabricantes. Assim, foi desenvolvido um estudo experimental focando a caracterização de duas macrofibras poliméricas disponíveis no mercado brasileiro. Focou-se o estudo na determinação dos parâmetros geométricos e na caracterização mecânica através da determinação da resistência à tração e avaliação do módulo de elasticidade. Na caracterização geométrica foi adotada como referência a norma europeia EN14889-2:2006. As medições do comprimento se efetuaram por dois métodos: o método do paquímetro e o método de análise de imagens digitais, empregando um software para processamento das imagens. Para a medição do diâmetro, além das metodologias mencionadas, foi usado o método da densidade. Conclui-se que o método do paquímetro, com o cuidado de esticar previamente as macrofibras, e o método das imagens digitais podem ser igualmente utilizados para medir o comprimento. Já parar determinar o diâmetro, recomenda-se o método da densidade. Quanto à caracterização mecânica, foi desenvolvida uma metodologia própria a partir de informações obtidas de outros ensaios. Assim, efetuaram-se ensaios de tração direta nas macrofibras coladas em molduras de tecido têxtil. Complementarmente, foi avaliado também o efeito do contato abrasivo das macrofibras com os agregados durante a mistura em betoneira no comportamento mecânico do material. Também se avaliou o efeito do método de determinação da área da seção transversal nos resultados medidos no ensaio de tração da fibra. Conclui-se que o método proposto para o ensaio de tração direta da fibra é viável, especialmente para a determinação da resistência à tração. O valor do módulo de elasticidade, por sua vez, acaba sendo subestimado. A determinação da área da seção da fibra através do método da densidade forneceu também os melhores resultados. Além disso, comprovou-se que o atrito das fibras com o agregado durante a mistura compromete o comportamento mecânico, reduzindo tanto a resistência quanto o módulo de elasticidade. Assim, pode-se afirmar que a metodologia proposta para o controle geométrico e mecânico das macrofibras poliméricas é adequada para a caracterização do material. / A wide variety of synthetic macrofibers for concrete reinforcement are available nowadays. By nature, these fibers exhibit great diversity of properties and characteristics. These variations affect its performance as reinforcement in concrete. However, there are no Brazilian standards on the subject and characterization methodologies available in foreign standards present divergences. Some standards define that the characterization of the mechanical behavior should be made in the original filaments and others that the test should be performed according methods for metallic materials characterization. The standard EN14889-2:2006 provides greater coverage about the subject, but leaves doubts about the suitability of the geometric characterization criteria of the fibers and does not set a specific testing method for its mechanical characterization. Thus, there is a need to establish a methodology that allows to carry out a quality control program of the fiber in the onsite conditions. This approach would also provide a way of materials characterization for experimental studies, which would allow better scientific basis of these works, which often rely exclusively on data taken from manufacturers. Thus, an experimental study focusing on the characterization of two polymer macrofibers available in Brazil was developed. The study aims at the determination of the geometrical and mechanical characteristics, such as the tensile strength and the elastic modulus. The geometric characterization was based on the prescriptions of the European standard EN14889- 2:2006. Measurements of length were made by two methods: the caliper method and digital image analysis method, employing software for image processing. For the measurement of the diameter, besides the aforementioned methodologies, the density method was also used. It is concluded that the caliper method, taking care to stretch the macrofibers previously, and the method of digital images can also be used to measure the length. To determine the diameter, it is recommended the density method. As for the mechanical characterization, a methodology was developed taking in consideration the previous information related to other tests. Thus, the direct tensile test was carried out in macrofibers glued in textile fabric frames. In addition, it was also evaluated the effect of the abrasive contact of macrofibers with the aggregates during mixing on the mechanical behavior of the material. Also, the effect of the method of determining the cross-sectional area in the results measured in fiber tensile test was evaluated. It is concluded that the proposed method for direct tensile test of the fiber is feasible, especially for tensile strength assessment. The value of the modulus of elasticity, in turn, has been underestimated. The determination of the fiber section area through the density method also gave the best results. Furthermore, it was found that the friction of the fibers with aggregate during mixing compromises the mechanical behavior reducing both strength and elastic modulus. Thus, it can be said that the proposed methodology for the geometric and mechanical control of polymer macrofibers is suitable for the material characterization.

Dans ce travail, la caractérisation mécanique de l’interphase entre les zones amorphes et cristallines dans le polyéthylène a été abordée. La caractérisation élastique est effectuée en appliquant deux approches micromécaniques à partir des données de la simulation moléculaire pour la zone interlamellaire. Ces approches micromécaniques sont d’une part le modèle étendu d’inclusion composite, et d’autre part la méthode de double inclusion. Les résultats des deux approches s’accordent parfaitement. Il a été mis en évidence que le tenseur de rigidité de l’interphase n’est pas défini positif, l’interphase est donc mécaniquement instable. La comparaison avec les résultats expérimentaux valide la méthodologie proposée. Pour la caractérisation hyperélastique, l’algorithme hybride proposé consiste à appliquer la loi de comportement d’un milieu continu isotrope, compressible et hyperélastique aux résultats de la simulation de la dynamique moléculaire d’un élément unitaire de polyéthylène. La notion d’optimisation d’un ensemble de fonctions coûts non négatives est l’idée clé de cette partie. Les paramètres hyperélastiques identifiés sont en bon accord avec ceux qui ont été estimés expérimentalement. L’évolution des frontières de l’interphase avec la déformation est le second résultat de cette analyse. La fin du travail est dédiée à la simulation numérique de la grande déformation viscoplastique d’un agrégat de polyéthylène. Le modèle de Gent adopté pour la contrainte de rappel, le tenseur de projection proposé pour l’approche modifiée de Taylor, et l’optimisation multiniveau font parties des contributions apportées. / Elastic characterization of the interphase layer in polyethylene is implemented by applying the relationships of two micromechanical approaches, “Extended Composite Inclusion Model” and “Double-Inclusion Method”, to the Monte Carlo molecular simulation data for the interlamellar domain. The results of the two approaches match perfectly. The interphase stiffness lacks the common feature of positive definiteness, which indicates its mechanical instability. Comparison with experimental results endorses the proposed methodology. For the hyperelastic characterization of the interlamellar domain and the interphase layer, the proposed hybrid algorithm consists in applying the constitutive equations of an isotropic, compressible, hyperelastic continuum to the molecular dynamics simulation results of a polyethylene stack. Evolution of the interphase boundaries are introduced as auxiliary variables and the notion of minimizing a set of nonnegative objective functions is employed for parameter identification. The identified hyperelastic parameters for the interlamellar domain arein good agreement with the ones that have been estimated experimentally. Finally, the large, viscoplastic deformation of an aggregate of polyethylene is reexamined. The Gent model adopted for the back stress of the noncrystalline phase, correcting the projection tensor for the modified Taylor approach, and the idea of multilevel optimization are among the contributions made.

Les CMC oxyde/oxyde sont de bons candidats pour des applications thermostructurales. Le comportement mécanique et les mécanismes d’endommagement de deux composites alumine/alumine à renforts tissés bi- et tridimensionnels ont été étudiés et comparés. La microstructure de ces CMC à matrice faible a été caractérisée à partir de porosimétrie et de CND, tel que thermographie IR, scan ultrasonore et tomographie X, ce qui a permis de mettre en évidence la présence de défauts initiaux. Le comportement mécanique en traction, ainsi qu’en compression dansle cas du CMC à renfort bidimensionnel, dans la direction des fibres ainsi que dans la direction ±45°, aété étudié à température ambiante. Afin d’exploiter pleinement ces essais, nous avons eu recours à plusieurs méthodes d’extensométrie et de suivi d’endommagement, telles que la thermographie IR et l’émission acoustique. Les propriétés mécaniques à rupture ainsi que le module de Young du CMC à renfort bidimensionnel développé à l’Onera se sont avérées supérieures à celles disponibles dans la littérature. Les mécanismes d’endommagement des matériaux ont été déterminés à partir d’observations post mortem au MEB et d’essais in situ dans un MEB, ce qui a permis d’évaluer la nocivité des défauts initiaux. Enfin, l’étude du comportement mécanique de ces composites a permisde proposer un modèle d’endommagement tridimensionnel qui permettra de poursuivre le développement de ces matériaux grâce à du calcul de structure. A l’issue de cette thèse, des pistes d’amélioration des procédés d’élaboration et de choix d’instrumentation à utiliser pour les futures études, notamment en ce qui concerne le suivi d’endommagement, ont également été proposées. / Oxide/oxide CMCs are good candidates for thermostructural applications. Themechanical behaviour and damage mechanisms of two alumina/alumina composites with two andthree dimensional woven reinforcements were studied and compared. The microstructure of theseweak matrix CMCs was characterized by porosimetry and NDT methods, such as IR thermography,ultrasound scanning and X-ray tomography, which highlighted initial defects. The mechanicalbehaviour was studied through tensile tests, as well as compression tests in the case of the twodimensionalreinforced CMC. These tests were conducted at room temperature, in the fibres directionsand in the ±45° direction. In order to fully exploit these tests, several extensometry and damagemonitoring methods, such as IR thermography and acoustic emission, were used. Young’s moduli andmaximum stresses and strains of the two-dimensional reinforced CMC developed at Onera appearedto be higher than those available in the literature. The damage mechanisms of the materials weredetermined by post mortem SEM observations and in situ testing in a SEM, which made it possible toassess the nocivity of initial defects. Studying the mechanical behaviour of these composites finallyenabled the development of a three-dimensional damage model that will facilitate the furtherdevelopment of such materials, through finite element analysis. Finally, some improvements regardingthe manufacturing processes and the instrumentation for damage monitoring were suggested forfuture studies.

La suffusion est un cas particulier d'érosion interne qui apparait dans les ouvrages hydrauliques. Elle se caractérise par le détachement et le transport des particules fines à travers les gros grains sous l'action d'un écoulement hydraulique en laissant derrière un squelette granulaire dont les caractéristiques en termes de densité et d'arrangement géométrique granulaire ont été changées. De telles modifications dans la micro-structure du sol peuvent conduire à des déformations à l'échelle macroscopique et peuvent influencer le comportement mécanique du sol. Ce travail a été consacré à l'étude du mécanisme de suffusion et à son impact sur les propriétés mécaniques des sols non-cohésifs. Pour atteindre cet objectif, deux approches ont été suivies dans ce travail: l'une numérique et l'autre expérimentale. Un modèle numérique discret a été défini pour décrire quantitativement le comportement macroscopique du sol et analyser la micro-structure des assemblages granulaires. Il est basé sur l'utilisation de particules sphériques et la résistance au roulement aux contacts, ainsi que sur une nouvelle méthode de compactage des échantillons pour simuler celle utilisée au laboratoire, et atteindre une large gamme de densités initiales. Le modèle a été validé par comparaison de résultats numériques et de données expérimentales. Ce modèle a d'abord été appliqué sur des assemblages granulaires avec des teneur en fines différentes afin d'étudier le rôle des particules fines pour une micro-structure de sol donnée, sans tenir compte d'un processus d'érosion. Il a été montré qu'il existe un pourcentage de fines, en dessous de la teneur seuil, où des particules fines peuvent commencer à participer au transfert de force, et que, si la suffusion s'initie et mobilise ces particules, ceci pourra affecter le comportement macroscopique du sol. Par la suite, une cinétique simplifiée d'extraction du grain a été proposée pour décrire le processus de suffusion. Elle est basée sur une approche de couplage fluide-solide partielle. L'intérêt de cette procédure d'extraction est que, d'une part, elle tient en compte des critères géométriques et hydrauliques complexes; d'autre part, le modèle induit un coût de calcul raisonnable. Cette procédure a été validée sur la base d'essais expérimentaux de suffusion effectués avec un dispositif nouvellement développé. Les conséquences de cette érosion sur les propriétés mécaniques des sols ont été caractérisées par la réalisation en laboratoire et la simulation d'essais de compression triaxiale. Le développement de la suffusion et ses conséquences sur le comportement macroscopique sont discutés en terme de densité et granulométrie initiale du sol, de chargement hydraulique et du type de particules érodées (actives ou inactive vis-à-vis du transfert de force). / Suffusion is a particular case of internal erosion taking place in hydraulic earth structures. It is characterized by the detachment and migration of fine particles by interstitial flow leaving behind the granular skeleton. Such modifications in the soil microstructure may lead to deformations at the macroscopic scale and may influence the mechanical behavior of the soil. This research was devoted to investigate the suffusion mechanism and its impact on the mechanical properties of cohesionless soils. To achieve this objective, two approaches were followed in this work: numerical and experimental approaches. A discrete numerical model was defined to describe quantitatively the soil macroscopic behavior and to analyze the microstructure of granular assemblies. It is based on the use of spherical particles and contact rolling resistance, as well as a new method of compaction to mimic the one used in laboratory and to reach a wide range of initial densities. The model was validated through comparison of numerical results with experimental data. This model was first applied on granular assemblies with different fines contents to study the role of fine particles with respect to a given soil microstructure, without taking into account an erosion process. It was shown that there exists a fines content, below the threshold, where fine particles may start to participate in the force transfer that if suffusion initiates and mobilizes these particles, it may affect the macroscopic behavior of the soil. Thereafter, a simplified kinetics of grain extraction was proposed to describe the suffusion process. It was based on a one-way fluid-solid coupling approach. The importance of this extraction procedure is that, on one hand, it takes into account complex geometric and hydraulic criteria; on the other hand, the model involves an affordable computational cost. This procedure was validated based on experimental tests carried out using a newly developed suffusion apparatus. Consequences of this erosion on the mechanical properties of soils were characterized from experimental and simulated triaxial compression tests. Suffusion development and its consequences on the macroscopic behavior are discussed from the results obtained in terms of the initial soil density and gradation, the hydraulic loading and the type of eroded particles (active or inactive in the force transfer).

Cette thèse CIFRE a été réalisée dans le cadre d'un partenariat entre l'ENTPE Université de Lyon, AREA et EIFFAGE Travaux Publics. Les méthodes actuelles de détermination et de prévision de l'endommagement des structures de chaussées autoroutières sont peu fiables et nécessitent d'être améliorées. L'objectif de la thèse est de mettre en place une procédure d'analyse inverse donnant accès aux paramètres de comportement des matériaux de chacune des couches de chaussées à partir des mesures de déflexion. Une première étape vise à définir plus précisément les états de contraintes et de déformations existants dans les différentes couches de chaussées. Pour cela, une instrumentation de chaussée autoroutière située proche d'Aix les Bains a été réalisée. 47 capteurs de déformation et de température ont été implantés dans la structure à trois niveaux différents lors de travaux d'entretien effectués en août 2012. En parallèle, des matériaux de chaussée ont été prélevés sur autoroutes pour caractériser leur comportement en laboratoire. Des essais de module complexe ont permis de déterminer les propriétés thermo-visco-élastiques des matériaux. Ces résultats ont permis de modéliser la déformation de la chaussée et de la comparer avec les mesures. Des mesures de déflexion ont également été réalisées sur la chaussée instrumentée à l'aide d'un curviamètre. Les résultats ont pu être comparés à la modélisation. Les différences observées ont permis de proposer une analyse critique des mesures de déflexion. / This thesis was conducted into a parnership between ENTPE university of Lyon, AREA and Eiffage Travaux Publics. Current methods of determination and prediction of damage to highway pavement structures are unreliable and need to be improved. The aim of the thesis is to establish an back analysis procedure from the deflection measurements fiving access to material behavior parameters of each pavement layers. A first step is to define more precisely the states of stress and deformation existing in the different layers of pavement. For this reason, a motorway pavement instrumentation was performed near Aix les Bains in France. 47 strain sensors and temperature were implanted into the structure in three layers during maintenance works in August 2012.In parallel, pavement materials were collected on motorways to characterize their behavior. Complex modulus tests were used to determine the thermo-viscoelalstic properties of materials. These results were used to modeling the deformation of the pavement and compared with measurements. Deflection measurements were also performed on the instrumented pavement with a curviameter device. The reseults were compared to modeling. The observed differences have helped to provide a critical analysis of deflection measurements.

Uma grande diversidade de macrofibras poliméricas para reforço de concreto se encontram disponibilizadas hoje em dia. Por natureza estas fibras apresentam grande diversidade de características e propriedades. Estas variações afetam sua atuação como reforço no concreto. No entanto, não há normas brasileiras sobre o assunto e as metodologias de caracterização de normas estrangeiras apresentam divergências. Algumas normas definem que a caracterização do comportamento mecânico deva ser feita nos fios originais e outras que se devam utilizar métodos definidos para caracterização de materiais metálicos. A norma EN14889-2:2006 apresenta maior abrangência, mas deixa dúvidas quanto à adequação dos critérios de caracterização geométrica das fibras e não define um método de ensaio específico para sua caracterização mecânica. Assim, há a necessidade de estabelecimento de uma metodologia que permita a realização de um programa de controle de qualidade da fibra nas condições de emprego. Esta metodologia também proporcionaria uma forma de caracterização do material para estudos experimentais, o que permitiria maior fundamentação científica desses trabalhos que, frequentemente, fundamentam-se apenas em dados dos fabricantes. Assim, foi desenvolvido um estudo experimental focando a caracterização de duas macrofibras poliméricas disponíveis no mercado brasileiro. Focou-se o estudo na determinação dos parâmetros geométricos e na caracterização mecânica através da determinação da resistência à tração e avaliação do módulo de elasticidade. Na caracterização geométrica foi adotada como referência a norma europeia EN14889-2:2006. As medições do comprimento se efetuaram por dois métodos: o método do paquímetro e o método de análise de imagens digitais, empregando um software para processamento das imagens. Para a medição do diâmetro, além das metodologias mencionadas, foi usado o método da densidade. Conclui-se que o método do paquímetro, com o cuidado de esticar previamente as macrofibras, e o método das imagens digitais podem ser igualmente utilizados para medir o comprimento. Já parar determinar o diâmetro, recomenda-se o método da densidade. Quanto à caracterização mecânica, foi desenvolvida uma metodologia própria a partir de informações obtidas de outros ensaios. Assim, efetuaram-se ensaios de tração direta nas macrofibras coladas em molduras de tecido têxtil. Complementarmente, foi avaliado também o efeito do contato abrasivo das macrofibras com os agregados durante a mistura em betoneira no comportamento mecânico do material. Também se avaliou o efeito do método de determinação da área da seção transversal nos resultados medidos no ensaio de tração da fibra. Conclui-se que o método proposto para o ensaio de tração direta da fibra é viável, especialmente para a determinação da resistência à tração. O valor do módulo de elasticidade, por sua vez, acaba sendo subestimado. A determinação da área da seção da fibra através do método da densidade forneceu também os melhores resultados. Além disso, comprovou-se que o atrito das fibras com o agregado durante a mistura compromete o comportamento mecânico, reduzindo tanto a resistência quanto o módulo de elasticidade. Assim, pode-se afirmar que a metodologia proposta para o controle geométrico e mecânico das macrofibras poliméricas é adequada para a caracterização do material. / A wide variety of synthetic macrofibers for concrete reinforcement are available nowadays. By nature, these fibers exhibit great diversity of properties and characteristics. These variations affect its performance as reinforcement in concrete. However, there are no Brazilian standards on the subject and characterization methodologies available in foreign standards present divergences. Some standards define that the characterization of the mechanical behavior should be made in the original filaments and others that the test should be performed according methods for metallic materials characterization. The standard EN14889-2:2006 provides greater coverage about the subject, but leaves doubts about the suitability of the geometric characterization criteria of the fibers and does not set a specific testing method for its mechanical characterization. Thus, there is a need to establish a methodology that allows to carry out a quality control program of the fiber in the onsite conditions. This approach would also provide a way of materials characterization for experimental studies, which would allow better scientific basis of these works, which often rely exclusively on data taken from manufacturers. Thus, an experimental study focusing on the characterization of two polymer macrofibers available in Brazil was developed. The study aims at the determination of the geometrical and mechanical characteristics, such as the tensile strength and the elastic modulus. The geometric characterization was based on the prescriptions of the European standard EN14889- 2:2006. Measurements of length were made by two methods: the caliper method and digital image analysis method, employing software for image processing. For the measurement of the diameter, besides the aforementioned methodologies, the density method was also used. It is concluded that the caliper method, taking care to stretch the macrofibers previously, and the method of digital images can also be used to measure the length. To determine the diameter, it is recommended the density method. As for the mechanical characterization, a methodology was developed taking in consideration the previous information related to other tests. Thus, the direct tensile test was carried out in macrofibers glued in textile fabric frames. In addition, it was also evaluated the effect of the abrasive contact of macrofibers with the aggregates during mixing on the mechanical behavior of the material. Also, the effect of the method of determining the cross-sectional area in the results measured in fiber tensile test was evaluated. It is concluded that the proposed method for direct tensile test of the fiber is feasible, especially for tensile strength assessment. The value of the modulus of elasticity, in turn, has been underestimated. The determination of the fiber section area through the density method also gave the best results. Furthermore, it was found that the friction of the fibers with aggregate during mixing compromises the mechanical behavior reducing both strength and elastic modulus. Thus, it can be said that the proposed methodology for the geometric and mechanical control of polymer macrofibers is suitable for the material characterization.