L'objectif de cette thèse est d'observer l'impact des coups de couteaux sur différents tissus en aramide et d'analyser les facteurs influents. On peut se défendre d'une attaque mais une blessure ne peut être complètement évitée. L'objectif est d'absorber un maximum d'énergie, de façon à réduire le risque de blessure. Les mécanismes de perforation par une lame sont complexes. L'étude a révélé une demande dans ce domaine, car la plupart des solutions proposent des armures lourdes contenant du textile. Cet assemblage de matériaux a des inconvénients, comme le poids trop élevé et le manque de souplesse. D'autres chercheurs recommandent des solutions textiles parce qu'elles sont souples et déjà utilisées dans le domaine balistique. Les recherches menées pour cette thèse ont pour but de contribuer au développement de types de textile résistant aux coups de couteaux. C'est la raison pour laquelle, non seulement les propriétés de la matière textile doivent être analysées, mais aussi l'attaque au couteau en elle-même, pour développer une meilleure protection. Il a été démontré que beaucoup de facteurs influent sur le niveau de protection et rendent sa perception difficile. Des recherches ont été réalisées pour évaluer les paramètres de test, qui sont définis dans le test standard, mais aussi pour ceux qui n'y sont pas définis. / The research goal of this thesis is to examine various aramid fabrics with regard to their stabbing behaviour and to find influencing factors to this. An attack can only be inhibited, but an injury cannot be completely prevented. The goal is always to absorb as much energy as possible, so that the penetration is thus reduced and the risk of injury decreases. The stab mechanism is a complex and variable process. The review showed the demand on research in this area, because the most solutions involve hard body armour parts in combination with fibrous materials. This material combinations show many disadvantages with regards to the high weight and the missing flexibility. Other researchers also recommend textile solutions, because they are flexible and in the field of ballistic panels they are already used. The investigations carried out within this thesis are done to contribute to the development of pure textile stab-resistant panels. Therefore the interdependencies between the physical properties of the material but also the mechanism during a stab attack have to be recognized, to developed higher protection levels. It was shown, that the multitude of factors causes the problem to define a level of protection. General investigations were done to analyse the test parameters, which are defined in the test standard but also this one, which are missing.

This research involves the study of the short term loaded behaviour of mechanically degraded reinforced concrete (RC) flexural elements, which are strengthened with fibre reinforced polymer (FRP) composites. The two main objectives have been: (a) to conduct a series of realistic tests, the results of which would be used to establish the design criteria, and (b) to carry out analytical modelling and hence develop a set of suitable design equations. It is expected that this work will contribute towards the establishment of definitive design guidelines for the strengthening of reinforced concrete structures using advanced fibre composites. The experimental study concentrated on the laboratory testing of 30 simply supported, and 4 two-span continuous full size RC beams, which were strengthened by either FRP plates or fabric sheets. The failure modes of these beams, at ultimate limit state, were examined and the influencing factors were identified. A premature and extremely brittle collapse mechanism was found to be the predominant type of failure for beams strengthened with a large area of FRP composites. A modified semi-empirical approach was presented for predicting the failure load of such over strengthened beams. Despite the lack of ductility in fibre composites, it was found that the FRP strengthened members would exhibit acceptable ductile characteristics, if they were designed to be under strengthened. A new design-based methodology for quantifying the deformability of FRP strengthened elements was proposed, and its difference to the conventional concept of ductility was discussed. The available techniques for ductility evaluation of FRP strengthened concrete members were reviewed and a suitable method was recommended for determining ductility level of FRP strengthened members. A non-linear material based analytical model was developed to simulate the flexural behaviour of the strengthened and control beams, the results were seen to match very well. The parametric study provided an insight into the effects of various factors including the mechanical properties and cross sectional area of FRP composites, on the failure modes and ductility characteristics of the strengthened beams. Based on the findings of the experimental and analytical studies, design equations in the BS 8110 format were developed, and design case studies have been carried out. It was concluded that fibre composites could effectively and safely strengthen mechanically degraded reinforced concrete structures if appropriately designed. The modes of failure and the degree of performance enhancement of FRP strengthened beams depend largely on the composite material properties as well as the original strength and stiffness of the RC structure. If the FRP strengthened elements were designed to be under-strengthened, then the premature and brittle failure mode could be prevented and ductile failure mode could be achieved. It was also found that existing steel reinforcement would always yield before the FRP composite reached the ultimate strength. Furthermore, a critical reinforcement ratio, above which FRP strengthening should not be carried out, was defined. It was concluded that FRP strengthening is most suitable for reinforced concrete floor slabs, bridge decks, flanged beams and other relatively lightly reinforced elements. The study also revealed that to avoid a brittle concrete failure, existing doubly reinforced members should not be strengthened by FRP composites.

Made available in DSpace on 2014-12-17T14:58:15Z (GMT). No. of bitstreams: 1 JoseHBL_DISSERT_PARCIAL.pdf: 2505963 bytes, checksum: 1b82ec8a8147b2b7e13d0af6880855f0 (MD5) Previous issue date: 2012-05-02 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / Materials denominated technical textiles can be defined as structures designed and developed with function to fulfill specific functional requirements of various industrial sectors as are the cases of the automotive and aerospace industries. In this aspect the technical textiles are distinguished from conventional textile materials, in which the aesthetic and of comfort needs are of primordial importance. Based on these considerations, the subject of this dissertation was established having as its main focus the study of development of textile structures from aramid and glass fibers and acting in order to develop the manufacture of composite materials that combine properties of two different structures, manufactured in an identical operation, where each structure contributes to improving the properties of the resulting composite material. Therefore were created in laboratory scale, textile structures with low weight and different composition: aramid (100%), glass (100%) and aramid /glass (65/35%), in order to use them as a reinforcing element in composite materials with polyester matrix. These composites were tested in tension and its fracture surface, evaluated by MEV. Based on the analysis of mechanical properties of the developed composites, the efficiency of the structures prepared as reinforcing element were testified by reason of that the resistance values of the composites are far superior to the polyester matrix. It was also observed that hybridization in tissue structure was efficient, since the best results obtained were for hybrid composites, where strength to the rupture was similar to the steel 1020, reaching values on the order of 340 MPa / Os materiais denominados t?xteis t?cnicos podem ser definidos como estruturas projetadas e desenvolvidas com a fun??o de atender a requisitos funcionais espec?ficos de diversos setores da ind?stria, caso da ind?stria automotiva e aeroespacial. Nesse aspecto, distinguem-se dos materiais t?xteis convencionais, nos quais as necessidades est?ticas e de conforto t?m import?ncia primordial. Com base nessas considera??es, o tema dessa disserta??o foi estabelecido tendo como enfoque principal o estudo do desenvolvimento de estruturas t?xteis a partir de fibras de aramida e de vidro, atuando no sentido de elaborar a fabrica??o de materiais comp?sitos que combinem propriedades de duas estruturas diferentes, fabricadas em uma mesma opera??o, onde cada estrutura contribui para melhoria das propriedades do material comp?sito resultante. Para tanto foram desenvolvidas em escala laboratorial estruturas t?xteis de baixa gramatura e composi??o diferenciada de aramida (100%), vidro (100%) e aramida/vidro (65/35%) para utiliza??o como elemento refor?ante em comp?sitos com matriz de poli?ster. Os comp?sitos produzidos foram ensaiados em tra??o e sua superf?cie de fratura avaliada por MEV. Com base nas analises das propriedades mec?nicas dos comp?sitos desenvolvidos, observou-se a efici?ncia das estruturas ou elaboradas como elemento refor?ante tendo em vista que os valores de resist?ncia dos comp?sitos foram muito superiores ? matriz de poli?ster. Tamb?m foi observado que a hibridiza??o na estrutura dos tecidos foi eficiente, uma vez que os melhores resultados obtidos foram para os comp?sitos h?bridos, onde a resist?ncia na ruptura foi semelhante ? do a?o 1020, atingindo valores na ordem de 340 MPa

Made available in DSpace on 2014-12-17T14:58:20Z (GMT). No. of bitstreams: 1 AlanJLM_DISSERT.pdf: 1835050 bytes, checksum: 47bf4fbd76665d11995bd7eb5bd3522a (MD5) Previous issue date: 2013-07-23 / Materials known as technical textiles can be defined as structures designed and developed to meet specific functional requirements of various industry sectors, which is the case in automotive and aerospace industries, and other specific applications. Therefore, the purpose of this work presents the development and manufacture of polymer composite with isophthalic polyester resin. The reinforcement of the composite structure is a technical textile fabric made from high performance fibers, aramid (Kevlar 49) and glass fiber E. The fabrics are manufactured by the same method, with the aim of improving the tensile strength of the resulting polymer composite material. The fabrics, we developed some low grammage technical textile structures in laboratory scale and differentiated-composition type aramid (100%), hybrid 1 aramid fiber / glass (65/35%) and hybrid 2 aramid fiber / glass (85/15% ) for use as a reinforcing element in composite materials with unsaturated isophthalic polyester matrix. The polymer composites produced were tested in uniaxial tensile fracture surface and it?s evaluated by SEM. The purpose of this work characterize the performance of polymer composites prepared, identifying changes and based on resistance to strain corresponding to the mechanical behavior. The objectives are to verify the capability of using this reinforcement structure, along with the use of high performance fibers and resin in terms of workability and mechanical strength; verify the adherence of the fiber to the matrix and the fracture surface by electron microscopy scanning and determination of tensile strength by tensile test. The results indicate that, in a comparative study to the response of uniaxial tensile test for tensile strength of the composites and the efficiency of the low percentage of reinforcement element, being a technical textile fabric structure that features characteristic of lightness and low weight added in polymer composites / Os materiais denominados de tecidos t?cnicos podem ser definidos como estruturas projetadas e desenvolvidas com a fun??o de atender a requisitos funcionais espec?ficos de diversos setores da ind?stria com aplica??es espec?ficas. Nesse sentido, este trabalho apresenta o desenvolvimento e a fabrica??o de comp?sito polim?rico com resina poli?ster isoft?lico. O refor?o do comp?sito ? uma estrutura de tecido t?xtil t?cnico confeccionado com fibras de alto desempenho de aramida (Kevlar 49) e fibra de vidro E. Os tecidos s?o fabricados pelo mesmo m?todo, com o objetivo do aprimorar a resist?ncia a tra??o do material comp?sito polim?rico resultante. Os tecidos, foram desenvolvidos em escala laboratorial com baixa gramatura e composi??o diferenciada de aramida (100%), h?brido 1 fibra de aramida/vidro (65/35%) e h?brido 2 fibra de aramida/vidro (85/15%) para utiliza??o como elemento refor?ante em comp?sitos com matriz de poli?ster insaturada isoft?lico. Os comp?sitos polim?ricos produzidos foram ensaiados em tra??o uniaxial e sua superf?cie de fratura avaliada por MEV. A proposta do trabalho ? caracterizar o desempenho dos comp?sitos polim?ricos elaborados, identificando as altera??es e baseando-se na resist?ncia ao ensaio de tra??o correspondente a comportamento mec?nico. Os objetivos s?o verificar a potencialidade da utiliza??o desta estrutura de refor?o, juntamente com a utiliza??o das fibras de alto desempenho e a resina, em termos de trabalhabilidade e resist?ncia mec?nica; verificar a ader?ncia da fibra ? matriz e a superf?cie de fratura atrav?s de microscopia eletr?nica de varredura e determina??o de resist?ncia ? ruptura por ensaio de tra??o. Os resultados indicam que, em um estudo comparativo para a resposta dos ensaios mec?nicos de tra??o uniaxial h? resist?ncia ? ruptura dos comp?sitos e a efici?ncia da baixa porcentagem do elemento de refor?o, sendo uma estrutura de tecido t?xtil t?cnico que apresenta caracter?stica de leveza e baixa gramatura adicionada nos comp?sitos polim?ricos

Ce travail a pour objectif d’étudier le comportement mécanique d’un fil de para-aramide en sollicitation longitudinale et dynamique. Pour ce faire, nous avons conçu un nouveau dispositif expérimental permettant de réaliser ces essais à l’aide d’un canon à gaz : le Dispositif de Traction par Impact sur Fil (DTIF). Ce dispositif a subi de nombreuses modifications dans le but d’obtenir des conditions d’essais optimales. Celui-ci est associé à un dispositif de mesure par laser permettant d’obtenir le profil de vitesse du projectile ainsi que les courbes caractéristiques de Force-Déformation du fil testé. La validité de la mesure est confirmée par comparaison aux résultats obtenus avec un vélocimètre à effet Doppler, dispositif permettant de mesurer directement et de façon précise le profil de vitesse du projectile. Plusieurs campagnes d’essais sont réalisées, à la fois dans le but d’identifier les caractéristiques dynamiques d’un fil seul, et dans le but de caractériser l’influence de l’arrangement structural d’un tissu sur le comportement dynamique d’un fil. Cette étude révèle l’intervention de trois principaux paramètres structuraux, qui sont la surface de contact inter-fils totale, le nombre de points de liage et les pressions inter-fils transverses et latérales au sein du tissu, influant sur quatre principaux critères de rupture du fil, qui sont les défauts de structure et les phénomènes d’hystérésis au sein du filament, les concentrations de contraintes ainsi que les forces de frottement au niveau des interactions entre le fil testé et le reste de la structure tissée. / This work aims at studying the mechanical behavior of a para-aramid yarn in dynamic and longitudinal load. To that end, we designed a new experimental device to achieve these tests with the use of a gas gun: the Tensile Impact Test for Yarn (TITY). This device met numerous modifications in the aim to reach optimal test conditions. It is associated with a measurement device using laser and allowing obtaining the velocity profile of the projectile and the Strength-Strain characteristic curves of the tested yarn. The validity of the measure is confirmed by comparing our results with those obtained with a laser Doppler vélocimètre, device allowing measuring directly and precisely the velocity profile of the projectile. Many test campaigns are performed. Both in the aim to identify the dynamic parameters of a single and virgin yarn, and in the aim to characterize the impact of the fabric structural arrangement on the dynamic behavior of a yarn. This study reveals the intervention of three main structural parameters, which are the total inter-yarns contact surface, the number of binding points and the transvers and lateral inter-yarns pressures, having an impact on four main yarn break criteria, which are the structural defects and hysteresis phenomena inside the filament, stress concentrations and frictional forces concerning the interactions between the tested yarn and the rest of the fabric.

Compression strength after impact tests were conducted on unidirectional composite rods with sleeves. These elements represent local members of open three-dimensional composite lattice structures (e.g., based on isogrid or IsoTruss® technologies). The unidirectional cores composed of carbon, glass, or basalt fiber/epoxy composites were co-cured in aramid sleeves. Sleeve patterns included both bi-directional (unsymmetric) braids and unidirectional spiral wraps with sleeve coverage ranging from nominally half to full. The diameters were nominally 8 and 11 mm (5/16 and 7/16 in). The larger diameter had nominally twice the cross-sectional area, to quantify the effects of scaling. The specimens were long enough to encourage local buckling failure as expected in members of typical composite lattice structures. The unsupported lengths varied from 127 mm (5.0 in) to 160 mm (6.3 in). Specimens were radially impacted at mid-length with energy levels ranging from 0 to 20 J (0 to 14.8 ft-lbs) and tested in longitudinal compression to quantify the effects of local impact damage on the buckling strength. In undamaged specimens, sleeve type and sleeve coverage have no effect on the ultimate compression strength of carbon, glass, or basalt composites (7% or less standard deviation for each material). When impacted, the influence of sleeve type and sleeve coverage varies with the type of fiber in the unidirectional core. Sleeve type and coverage did not affect the compression strength after impact for fiberglass composites. On the other hand, both carbon and basalt composites exhibited improved performance with braided (vs. spiral) sleeves (up to 34% stronger) and full (vs. half) coverage (up to 38% stronger). The compression strength of carbon configurations decreases with increasing impact energy regardless of sleeve type or coverage. The higher flexibility of glass and basalt composites, however, allowed some configurations to maintain the same compression strength after impact as their undamaged counterparts, at lower impact energy levels. Doubling cross-sectional area of basalt composites significantly improves the stiffness and compression strength after impact, more than doubling the impact energy required to achieve the same compression strength.

Nowadays, thin-walled load bearing structures can be realised using textile reinforced concrete (BRAMESHUBER and RILEM TC 201-TRC [1]). The required tensile strength is achieved by embedding several layers of textile. By means of the laminating technique the number of textile layers that can be included into the concrete could be increased. To further increase the first crack stress and the ductility as well as to optimize the crack development, fine grained concrete mixes with short fibres can be used. By a schematic stress-strain curve the demands on short fibres are defined. Within the scope of this study, short fibres made of glass, carbon, aramid and polyvinyl alcohol are investigated in terms of their ability to fit these requirements. On the basis of these results, the development of hybrid fibre mixes to achieve the best mechanical properties is described. Additionally, a conventional FRC with one fibre type is introduced. Finally, the fresh and hardened concrete properties as well as the influence of short fibres on the load bearing behaviour of textile reinforced concrete are discussed.

The flexural performance of composite systems made of reinforced concrete, Fibre Reinforced Polymers (FRPs) and adhesives was studied during the current research. The experimental investigation was principally concentrated on the potential use of Kevlar® 49 (aramid fibre) for RC beam strengthening. The main aims of research have been; (a) to investigate the relative merits of using Aramids in comparison to other FRPs, (b) strength optimisation of systems to prevent excessive losses of ductility, (c) to examine the failure mode and crack patterns, together with salient strength factors at ultimate limit state and (d) to carry out analytical modelling using a commercial FE package. The experimental investigation comprised of testing 55 simply supported RC beams of either 1.5m or 2.6m length. In addition to the parametric studies included in points (a)-(d) above (to assess the section characteristics), further experimentation was conducted to investigate the beam performance by varying the factors of; (e) beam shear span, (f) FRP anchorage length, (g) concrete surface preparation, (h) FRP end-anchoring, (i) beam precracking, (j) introduction of air-voids within the bond line of FRP/concrete, (k) influence of cyclic loading and, (1) exposure to aggressive environment. The results from current tests confirm elements of reports from other researchers (by thorough review of literature) that all FRPs have great potential for flexural strengthening of RC members. This is valid even in cases where additional environmental degradation and/or cracking (due to serviceability loads), had taken place. Aramid fibres were found to result in favourable outcomes concerning both strength and ductility enhancements. It was determined, both from experiments and non-linear modelling, that the amount of FRP fibre content is an important factor in every strengthening application. Experimentation showed that depending on the existing condition of the structure (concrete strength, internal reinforcement ratio, section dimensions, degradation level and load configuration), there seems to be a unique level of optimum fibre content. The FRP levels in excess of the optimum were seen to lead to premature brittle tearing-off failure modes. It was also found that to prevent premature beam failure (due to incompatibility of stress at concrete and FRP interface), a maximum possible anchorage length should be considered in order to deliver an optimum section performance. The results from the analytical modelling indicated a most satisfactory agreement with the experimental data after the initial mechanical properties were calibrated. It was found that actual representation of material properties (e.g. steel constitutive law) are of great significance, for an accurate modelling of RC element loaded behaviour. The bond developed between the FRP and concrete is one of the key parameters for achieving good performance of the systems. It was determined that concrete surface preparation and priming is beneficial, while the introduction of air-voids due to poor workmanship can reduce the section load bearing capabilities. Cyclic loading on FRP strengthened sections was found to curtail the full rotational capacity utilisation of the beam. However, even the above mentioned curtailed behaviour was more advantageous than cyclically loaded beam performance without FRP strengthening.

Nowadays, thin-walled load bearing structures can be realised using textile reinforced concrete (BRAMESHUBER and RILEM TC 201-TRC [1]). The required tensile strength is achieved by embedding several layers of textile. By means of the laminating technique the number of textile layers that can be included into the concrete could be increased. To further increase the first crack stress and the ductility as well as to optimize the crack development, fine grained concrete mixes with short fibres can be used. By a schematic stress-strain curve the demands on short fibres are defined. Within the scope of this study, short fibres made of glass, carbon, aramid and polyvinyl alcohol are investigated in terms of their ability to fit these requirements. On the basis of these results, the development of hybrid fibre mixes to achieve the best mechanical properties is described. Additionally, a conventional FRC with one fibre type is introduced. Finally, the fresh and hardened concrete properties as well as the influence of short fibres on the load bearing behaviour of textile reinforced concrete are discussed.

[pt] Neste trabalho é feito um estudo experimental da relaxação de uma fibra sintética de alta resistência, conhecida como Kevlar 49, empregada na fabricação de cabos que podem ser usados como cabos de protensão. O objetivo é obter uma equação para o cálculo da relaxação e verificar a influência de um condicionamento mecânico (aplicação e remoção de uma tensão). Foram realizados ensaios em seis amostras da fibra sob cinco níveis de tensão, equivalentes a 10%, 20%, 30%, 40% e 50% da tensão de ruptura do material. Os ensaios foram realizados com a temperatura e umidade relativa do ar controlados na faixa de 21oC + 2oC e 77% + 7% respectivamente. O tempo de duração de cada ensaio foi de 72 horas. Os resultados revelaram que as curvas de relaxação são lineares quando plotadas numa escala logarítmica do tempo e que o coeficiente de relaxação é bem representado por uma função potencial e depende da tensão aplicada. Em adição revelaram que um condicionamento mecânico não altera o comportamento da fibra. / [en] High-strength aramid fibers have been used in the production of a variety of cables and ropes which have found several applications as structural members in bridges and other types of structures. For such applications, a sound knowledge of the time dependent material properties is highly important. An experimental investigation on the stress relaxation behavior of a high-strength aramid fiber was carried out, with the purpose of studying the viscoelastic properties of the material and the effect of a mechanical conditioning (application and removal of stress prior to testing) on these properties. The fiber used in this investigation is commercially known as Kevlar 49. The tests were conducted at five different stress levels, at constant temperature and moisture. The results showed that the fiber has a non-linear viscoelastic behavior and that the effect of the mechanical conditioning isn´t important. An equation for the prediction of the stress relaxation is presented. / [es] En este trabajo se realiza un estudio experimental de la relajamiento de una fibra sintética de alta resistencia, conocida como Kevlar 49, empleada en la fabricación de cables que pueden ser usados como cables de protensión. El objetivo es obtener una ecuación para el cálculo dela relajamiento y verificar la influencia de un condicionamento mecánico. Fueron realizados ensayos en seis muestras de la fibra bajo cinco niveles de tensión, equivalentes a 10%, 20%, 30%, 40% y 50% de la tensión de ruptura del material. Los ensayos fueron realizados con la temperatura y la humedad relativa del aire controlados en la faja de 21oC + 2oC y 77% + 7% respectivamente. El tiempo de duración de cada ensayo fue de 72 horas. Los resultados revelaron que las curvas de relajamiento son lineales cuando se utiliza una escala logarítmica para el tiempo y que el coeficiente de relajamiento está bien representado por una función potencial, que depende de la tensión aplicada. Adicionalmente, los ensayos revelaron que un condicionamento mecánico no altera el comportamiento de la fibra.