Dissertations / Theses on the topic 'Tensile tests'

Due to the findings of extensive damage on geogrids used in a road embankment in northern Sweden, the Swedish Transport Administration (TRV) started to investigate the reason of these damages. Since the geogrids were installed at low temperature, below 0°C, it was suspected that the damages were connected the low temperature. To analyse whether low temperatures have an influence on the extent of installation damages, both a half-scale setup and temperature controlled tensile tests have been carried out on geogrids. In total five different types of geogrids have been tested; 3 extruded polypropylene geogrids, 1 woven PET geogrid, and 1 welded PET geogrid. All geogrids had an aperture size of approximately 35 mm and specified tensile strength of approximately 40 kN/m. The Half-scale tests was conducted by building a small road embankment inside a freeze container, at the Luleå University of Technology (LTU). The embankment contained crushed aggregate, type 0-70 mm, and geogrids. The purpose of the half-scale test was to simulate installation of geogrids at different temperatures and thereby investigate whether low temperatures have an influence on the rate of installation damages. The half-scale test was done for each type of geogrid at the temperatures: +20°C, -20°C and -30°C. First, the geogrid was covered by 150 mm of crushed aggregate. Then a vibratory plate (160 kg) was used to compact the crushed aggregate. After each installation, the crushed aggregate was removed carefully by vacuum suction. The geogrid was removed and then analysed by visual control and tensile tests conducted according to ISO 10319:2008 (wide width tensile test). Results from the half-scale tests indicate that 2 out of 5 of the tested geogrids were affected by the testing procedure. The results indicate that: -        one of the geogrids of polyprophylene (here referred to as G2) was more damaged at lower temperatures compared to installation at +20° C. -        the geogrid of woven PET (here referred to as G5) was less damaged at lower temperatures compared to installation at +20° C. Results for the other geogrids are either inconsistent or shows no significant variation of the measured parameters as function of temperature. Hence, these results cannot be interpreted as damage during installation. Temperature controlled tensile tests were done by tensile testing single strands from the geogrids to failure, inside a temperature controlled chamber. The purpose of these tests was to investigate how the strength properties of the geogrids are affected by low temperature. The test was repeated 5 times for each geogrid and temperature (+20°C, 0°C, -10°C and -20°C). Force and strain was measured during the tests. The results from the temperature controlled tensile tests show that the maximum strain decreases with lower temperature for all tested geogrids. The maximum strain decreased by 16% - 49% when the temperature dropped from +20°C to -20°C. The results show that the tensile strength increases with lower temperature for all tested geogrids except for the welded PET geogrid (here referred to as G1). For G1 the tensile strength decreased by approximately 7% at a temperature drop from +20°C to -20°C. For the woven PET geogrid (G5) and the polypropylene geogrids (G2-G3) the tensile strength increased between 13%-45% at a temperature drop from +20°C to -20°C. The E-modulus increased at lower temperature for all tested geogrids. The secant E-modulus at 2% strain increased by 13%-71% at a temperature drop from +20°C to -20°C. Summarized conclusions from the tests: Strength properties changed for all tested geogrids as the temperature decreased. All tested geogrids got stiffer at lower temperatures. The magnitude of the effects is different for different geogrids. The tensile strength increased with lower temperature for all tested geogrids except for the welded PET geogrid, which got lower tensile strength at lower temperature. The half-scale test indicates that the amount of installation damages at geogrids can be dependent of the temperature at installation. However, these indications can only be seen at two out of five tested geogrids. The effect cannot be connected to a specific step in the installation procedure and cannot be explained by the results from the temperature controlled tensile tests. The results from the half-scale test have a statistically low reliability since only one installation for each temperature and geogrid type was done. The compaction equipment used during the test was small, and had low compaction energy compared to a vibratory roller compactor commonly used in construction work. With respect to the discussion above, further studies should be focusing on developing the half-scale test. It is suggested that the test is scaled up to a full-scale test in order to simulate a real installation as close as possible. The test should also be conducted several times for each geogrid at each temperature in order to enable statistical analyses.

Combining the most recent technologies in concrete, Ultra-High-Performance Fibre-Reinforced Concrete (UHPFRC) arises as a promising material for the near future. UHPFRC have shown how flexible concrete can be to adapt to the ever-changing social and environmental demands. With its high flexibility composition and its mechanical properties, UHPFRC is full of both unexplored and unexploited possibilities. Engineers should take responsibility for this task. However, it is fair to acknowledge that this is not an easy task and it requires the development of reliable and widely accepted design standards provided by the scientific community. A major concern about durability, long-lasting structures and reduction of maintenance cost, as well as the development of new concrete technologies, improved knowledge of fibre effect and a huge growth in the fibre industry accompanied by fibre price reduction have led, among other factors, to the development of new types of concrete whose mechanical behaviour substantially differs from conventional fibre-reinforced concrete. This is why current characterisation methodologies and design standards must be reviewed and adjusted to these newer materials. However, design standard revision cannot disregard former milestones achieved thanks to decades of hard work. It must offer an integrated view in which new types of concrete comprise existing ones in a broader group, because at the end of the day and despite having newer and improved properties, new types of concrete are still concrete. That is how it should be understood and how it must be reflected in newer codes and standards. The work presented herein is focused on one of these recently developed materials that embraces major advanced technologies in concrete: Ultra-High-Performance Fibre-Reinforced Concrete (UHPFRC). This work is specifically focused on those crucial requirements for the development and widespread use of it, such as constitutive tensile characterisation and classification. This work includes a deep revision of the uniaxial tensile behaviour of concrete and its development as fibre technology has evolved. In addition, traditional characterisation standard methods as well as those recently developed for its specific use on UHPFRC are reviewed and called into question. Throughout the document, the development of different methodologies to determine the uniaxial constitutive tensile behaviour of UHPFRC from bending tests are shown, together with a simplified characterisation proposal specially developed for being included in a standard. All developed methodologies presented herein are checked and validated. These methods are specifically designed for their application on experimental results obtained from a special type of four-point bending test, whose standardisation proposal for UHPFRC is also shown. Finally, a classification proposal is presented as a function of more relevant UHPFRC tensile parameters necessary for design that can be directly obtained from the standard characterisation test method suggested. Proposed classification encompasses the existing classification for conventional reinforced and fibre-reinforced concrete. In it, both plain concrete and fibre-reinforced concrete are presented as a particular case of a more general tensile constitutive response for concrete. Standard methodology and classification proposed are in accordance with the evolution of concrete and unify historic milestones achieved by the international research community.
El Hormigón de Muy Alto Rendimiento (HMAR) combina los últimos avances tecnológicos en hormigón y se erige como un material prometedor para el futuro. El HMAR ha demostrado su gran capacidad para adaptarse a las cada vez más exigentes demandas sociales y medioambientales. Con un gran abanico de posibilidades en su dosificación para conseguir las propiedades mecánicas deseadas, el HMAR es un material lleno de posibilidades aún sin explorar y sin explotar. Los ingenieros tienen la responsabilidad de esta tarea. Sin embargo, es justo reconocer que no se trata de una tarea fácil y que requiere de un desarrollo previo de códigos de diseño adecuados y ampliamente aceptados por parte de la comunidad científica. La aparición de nuevas tecnologías, el mayor conocimiento sobre la aportación de las fibras así como su industrialización y bajada de precios, las mayores preocupaciones sobre la durabilidad estructural, incremento de la vida útil o la reducción de los costes de mantenimiento, entre otros factores, han derivado en el desarrollo de nuevas tipologías de hormigones cuyo comportamiento mecánico difiere de manera sustancial de los tradicionales hormigones con fibras. Es por ello que tanto la readaptación de las metodologías de caracterización como las metodologías de diseño deben ser reformuladas. Y esto debe hacerse de manera no disruptiva, es decir, manteniendo la línea de los hitos alcanzados en los hormigones con fibras convencionales de manera que queden integrados en metodologías de caracterización y de diseño que los engloben, porque al fin y al cabo, y aunque con nuevas y mejores propiedades mecánicas, los nuevos hormigones siguen siendo hormigones. Así debe ser entendido y así debe quedar reflejado en las nuevas normativas. El presente trabajo se centra en uno de esos nuevos materiales desarrollados con el avance de las nuevas tecnologías como es el HMAR. En especial, este documento se centra en ese aspecto tan fundamental para el desarrollo de nuevos hormigones como es la caracterización mecánica y la tipificación. Este trabajo incluye una revisión del comportamiento mecánico uniaxial a tracción del hormigón y de su evolución con la aparición de las diferentes tecnologías. Además, se revisan y se ponen en cuestión los sistemas tradicionales de caracterización, así como los nuevos sistemas desarrollados en los últimos años para su empleo específico en el HMAR. A lo largo del documento se desarrollan diferentes metodologías para la obtención del comportamiento constitutivo a tracción del HMAR, así como la propuesta de una metdología simplificada de caracterización especialmente diseñada para ser incluida en una norma, todas ellas debidamente validadas. Estas metodologías son de aplicación específica a los resultados experimentales obtenidos mediante un ensayo a cuatro puntos sin entalla, cuya propuesta de estandarización para el HMAR ha sido también desarrollada. Finalmente, se presenta una propuesta de tipificación de acuerdo a los parámetros más relevantes del comportamiento a tracción del HMAR que son necesarios para el diseño y que pueden ser directamente obtenidos del ensayo de caracterización propuesto. Esta clasificación engloba a la clasificación existente para el hormigón armado convencional y los actuales hormigones con fibras, de manera que se presenta la actual definición de hormigón con fibras como un caso particular de estos nuevos hormigones, respetando al máximo la evolución de este material y aunando los logros conseguidos por la comunidad científica.
Dins de les combinacions de les tecnologies més recents en el formigó, el formigó de molt alt rendiment (UHPFRC) sorgeix com un material prometedor per al futur pròxim. L'UHPFRC ha demostrat poder ser un formigó flexible per adaptar-se a les sempre canviants demandes socials i mediambientals. Amb una gran flexibilitat en la seua composició i les seues propietats mecàniques, l`UHPFRC està ple de possibilitats de ser explorades i explotades. Els enginyers han de prendre la responsabilitat d'aquesta tasca. No obstant això, és just reconèixer que això no serà fàcil i requerirà el desenvolupament de normes de disseny fiables i àmpliament acceptades per la comunitat científica. Hi ha una gran preocupació al voltant de la durabilitat, la vida útil de les estructures i la reducció del cost de manteniment, juntament amb el desenvolupament de noves tecnologies de formigó, un millor coneixement de l'efecte de la fibra i un enorme creixement en la indústria de la fibra acompanyat per la reducció del preu de la fibra, han conduït, entre altres factors, al desenvolupament de nous tipus de formigons, el comportament mecànic dels quals es diferencia substancialment dels formigons reforçats amb fibres convencionals. És per això que les metodologies de caracterització actuals i les normes de disseny han de ser revisades i ajustades a aquests nous materials. No obstant això, la revisió del codis de disseny no pot prescindir de les antigues fites aconseguides gràcies a dècades de treball dur. S'ha d'oferir una visió integrada en la qual els nous tipus de formigons integren els ja existents en un grup més ampli, ja que, al cap i la fi i malgrat tenir propietats noves i millorades, els nous tipus de formigons són encara un tipus de formigó. Així es com s'hauria d'entendre i reflectir-se en els nous codis i normes. El treball presentat en aquest document es centra en un d'aquests materials que s'han desenvolupat recentment i que abasta les principals tecnologies avançades en el formigó: el Formigó de Molt Alt Rendiment Reforçat amb Fibres (UHPFRC). Aquest treball se centra específicament en els requisits fonamentals per al desenvolupament i l'ús generalitzat d'aquest, com ara la caracterització i classificació del comportament constitutiu a tracció. Aquest treball inclou una revisió profunda del comportament a tracció uniaxial del formigó i els seus canvis al temps que la tecnologia de les fibres ha evolucionat. A més, els mètodes tradicionals estàndard de caracterització, així com els recentment desenvolupats per al seu ús específic en l'UHPFRC són revisats i qüestionats. Al llarg del document, es mostra el desenvolupament de diferents metodologies per a determinar el comportament constitutiu a tracció uniaxial de l'UHPFRC, juntament amb una proposta de caracterització simplificada especialment desenvolupada per poder ser inclosa en normativa. Totes les metodologies desenvolupades presentades en aquest document han estat comprovades i validades. Aquests mètodes estan dissenyats específicament per a la seva aplicació en els resultats experimentals obtinguts a partir d'un tipus especial d'assaig de flexió a quatre punts, a més també s'inclou una proposta d'estandardització per a l'UHPFRC. Finalment, es presenta una proposta de classificació en funció dels paràmetres més rellevants del comportament a tracció de l'UHPFRC que són necessaris per al disseny i que es poden obtindre directament del mètode d'assaig estàndard suggerit per a la caracterització de l'UHPFRC. La classificació proposada té amb compte la classificació existent per al formigó armat convencional i el reforçat amb fibres. En ella, tant el formigó en massa com el formigó reforçat amb fibres es presenten com un cas particular d'una resposta constitutiva a tracció més general per al formigó. La metodologia estàndard i la classificació proposada estan d'acord amb l'evolució de formigó i unifica l
López Martínez, JÁ. (2017). CHARACTERISATION OF THE TENSILE BEHAVIOUR OF UHPFRC BY MEANS OF FOUR-POINT BENDING TESTS [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/79740
TESIS

Includes bibliographical references.
This dissertation investigates the soil mechanical properties of a sample of Berea Red soil and the most suitable methods of treatment to improve it. Special attention has been paid to lime stabilization and different curing techniques. Gradings, special indicators and California Bearing Ratios were determined on both natural and lime stabilized Berea Red soil. Consolidometer tests were performed on natural and lime or cement stabilized soil at various densities to establish the compressibility and collapse potential. A computer controlled Indirect Tensile Testing with data logging facilities was developed in apparatus order that some of the soil mechanical properties of Berea Red soil may be determined. Natural and stabilized Berea Red soil was tested in a monotonic and cyclic triaxial apparatus to determine the short and long stress strain characteristics.

Two blocks made of Ti6Al4V material produced by Norsk Titanium Components ned Direct Metal Deposition (DMD) production technology were delivered for this investigation. The main difference between the blocks was the different waiting time implemented in the production parameters. The different waiting time implied that the material were allowed to cool to a deisred Interpass Temperature (IT). The blocks are referred to as T200 and T600 after their lowest IT of <200 degrees celsius and 500-700 degrees celsius, respectively. Sintef Manufacturing Raufoss reported elongations of 5% and 8% in the deposition-direction of the two blocks, which was lower than the 10% elongation obtained for the building-direction. The objective was to find any explanations for the impaired ductility in the deposition-direction, and why T200 have a lower elongation than T600. To reveal differences in micro- macrostructure and deformation-mechanisms between the blocks was combined EBSD+In-situ. tensile tests the main tool. Complementary studies with optical microscopy of etched in-situ specimens were also performed.The work started with an extensive macroetching of different planes relative to the deposition-direction. This revealed a 3D-image of the epitaxially growing solidification structure of columnar prior beta grains. Measurements of grain size and morphology did not indicate significant differences between the blocks. Later was EBSD selected to prior beta grain boundaries for specimens at the center of the blocks. Measurements of the thickness of primary alfa phase also indicated small differences between the blocks. From this it was concluded that the different ITs lead to small differences in solidification structure and the amount of primary alfa phase in the center of the blocks.The EBSD + in-situ tensile tests were carried out for specimens fabricated from the blocks in the deposition direction, such that investigation could be performed in the XZ-plane. The force was applied parallel to the deposition direction X. The in-situ specimens in block T200 had a slightly higher position in the block giving a finer microstructure because of faster cooling rates. The T200 specimens also contained to deposition layers in contrast to only one in T600 specimens. This made a direct comparison difficult. However, from the four in-situ specimens investigated was the following concluded: specimens from T200 deformed more homogeneously on a macroscale. Correspondingly was more activity observed at prior beta grain boundaries for T600. The more active grain boundaries in T600 may result from the different cooling rates from the peak temperature. Slower cooling rates will give smaller prior beta grains decorated with more homogeneous alfa phase along the boundaries of T600 specimens. The frequently reported detrimental mismatch between soft and hard HCP-grains in titanium alloys were also observed. However, the orientation and morphology of these grains seems to play an important role. Cracks growing along prior beta grains were always located at the side having a non-Burgers orientation relationship. The lamellar basketweave microstructure also seem quite effective to stop cracks from growing further, because of the plates having distinct orientations.This work has also uncovered the transition in microstructure between the substrate plate and first deposition layer. The microstructure develops from a very fine bimodal plate structure, through a equiaxed region with small amounts of primary alfa phase, to early stages of the columnar beta grain configuration. The first columnar beta grains are very small in size compared to higher up in the block, and they contains very small amounts of primary alfa phase. However, the basketweave microstructure develops relatively close to the substrate plate.

This research focuses on a study of the material parameters of horse hoof. The study of the problem with the factors that affect to the fastening of the shoe is not performed. Three different tests are carried out to obtain the behavior of the horn wall of the horse hoof in different ways, under physiological conditions and variation of hydration level. The first one is a tensile test to obtain both the force/displacement relation and the stress/strain relation and the parameters derived from them. The second is a hardness test to determine how the material resists to several kinds of permanent-shape changes when a force is applied.Finally, a microscopic study is performed to analyze the fracture surface after testing the specimens. A meticulous analysis of the results and a broad comparison with several researches are performed. The end of the thesis work suggests future works needed to solve the problem.

Cette thèse a pour objet la mesure de déformations sans contact lors d'un essai de traction à l'aide de la méthode de corrélation d'images numériques DIC (Digital Image Correlation). Cette technologie utilise le repérage d'un motif aléatoire de tachetures pour mesurer avec précision les déplacements sur une surface donnée d'un objet subissant une déformation. Plus précisément, un algorithme DIC plus efficace a été formulé, appliqué et validé. La présente thèse comporte cinq parties consacrées au développement et à la validation du nouvel algorithme DIC: (a) la formulation mathématique et la programmation, (b) la vérification numérique, (c) la validation expérimentale, par essai de traction, en comparant les mesures DIC à celles obtenues par des jauges de déformation, (d) l'étude d'un procédé d'atomisation novateur pour générer de façon reproductible le motif de tachetures pour un repérage plus exact, et (e) l'analyse des sources d'erreur dans les mesures DIC. Plus précisément, l'algorithme DIC a servi à analyser, à titre d'exemple d'application, les propriétés mécaniques du polyméthyl métacrylate utilisé pour la reconstruction du squelette. Avec l'algorithme DIC, les images d'un objet sont acquises pendant la déformation de celui-ci. On applique ensuite des techniques d'optimisation non linéaire pour suivre le motif de tachetures à la surface des objets subissant une déformation en traction avant et après le déplacement. Ce procédé d'optimisation demande un choix de valeurs de déplacement initiales. Plus l'estimation de ces valeurs de déplacement initiales est juste, plus il y a de chances que la convergence du processus d'optimisation soit efficace. Ainsi, cette thèse présente une technique de traitement novatrice reposant sur une logique floue incluant aussi l'approximation des valeurs initiales du déplacement pour démarrer un processus itératif d'optimisation, ayant pour résultat une reproduction plus exacte et efficace des déplacements et des déformations. La formulation mathématique du nouvel algorithme a été développée et ensuite mise en œuvre avec succès dans le langage de programmation MATLAB. La vérification de l'algorithme a été faite à l'aide d'images de synthèse simu­lant des déplacements de corps rigides et des déformations de traction uniformes. Plus particulièrement, les images de déplacement simulaient (1) des déplacements de 0, 1 - 1 pixel en translation, (2) des angles de rotation de 0, 5 - 5°, et (3) de grandes déformations en traction de l'ordre de 5000 à 300000µE déformation, respectivement. Les processus de vérification ont démontré que le taux d'exactitude du nouvel algorithme DIC est supérieur à 99% en ce qui concerne les mesures des différents types et niveaux de déplacements simulés. Une validation expérimentale a été menée afin d'examiner l'efficacité de la nouvelle tech­nique dans des conditions réalistes. Des échantillons de PMMA normalisés, respectant la norme ASTM F3087, ont été produits, inspectés et soumis à une charge de traction jus­qu'à la rupture. La déformation de la surface des échantillons a été mesurée au moyen (a) du nouvel algorithme DIC, et (b) des techniques utilisant des jauges de déformation de type rosette. La force maximale moyenne et la limite de résistance mécanique des quatre échantillons étaient de 880 ± 110 N et 49 ± 7 MPa, respectivement. La limite moyenne de déformation mesurée par la jauge de déformation et provenant de l'algorithme DIC étaient de 15750±2570 et 19890±3790 µs déformation, respectivement. Des déformations d'un tel ordre sont courantes pour les matériaux polymériques, et jusqu'à maintenant, la technique DIC n'n’était pas développée pour faire des mesures de déformations aussi importantes. On a constaté que l'erreur relative de la mesure DIC, par rapport à la technique de la jauge de déformation, s'élevait à 26 ± 8%. Par ailleurs, le module de Young moyen et le coefficient de Poisson moyen mesurés en utilisant des jauges de déformations étaient de 3, 78 ± 0, 07 G Pa et 0, 37 ± 0, 02, alors qu'ils étaient de 3, 16 ± 0, 61 GPa et 0, 37 ± 0, 08, respectivement lorsque mesurés avec l'algorithme DIC. L'écart croissant entre les mesures de déformation DIC et celles obtenues au moyen de jauges de déformation est probablement lié à la dis­torsion graduelle du motif de tachetures à la surface des échantillons de traction. Par la suite, on a introduit un facteur de correction de 1, 27 afin de corriger l'erreur systématique dans les mesures de déformation provenant de l'algorithme DIC. La limite de déformation des mesures DIC a été rajustée à 15712±357 µs déformation avec un taux d'erreur moyen relatif de -0, 5 ± 7, 1 %, comparé aux déformations mesurées par la jauge de déformation. Le module de Young moyen et le coefficient moyen de Poisson de l'algorithme DIC et des mesures obtenues par la jauge de déformation ont par ailleurs été rajustés à 3, 8 ± 0, 4 GPa et 0, 368 ± 0, 025, respectivement. Au moyen d'un procédé d'atomisation, des taches de peinture ont été générées de façon reproductible sur la surface d'un objet. Une approche expérimentale de planification facto­rielle a été utilisée pour étudier le motif de tachetures (répartition et gradient de l'échelle des tons de gris) pour mesurer l'exactitude de l'algorithme DIC. Plus particulièrement, neuf motifs de tachetures différents ont été générés au moyen du procédé d'atomisation et testés pour la translation et la rotation de corps rigides. Les résultats ont révélé que l'erreur moyenne relative parmi les neuf motifs de tachetures variait de 1, 1 ± 0, 3% à -6, 5 ± 3, 6%. Le motif de tachetures préféré, lequel se démarquait par une large gamme de taches claires et de valeurs de tons de gris, a produit une erreur relative de 1, 1 ± 0, 3%. Une analyse des erreurs et des sources d'erreurs relatives de la mesure de l'algorithme DIC a été menée. Ti-ois catégories de sources d'erreurs, incluant l'algorithme lui-même, les paramètres du processus (taille des sous-ensembles, nombre de pixels calculés) et l'en­vironnement physique (uniformité des échantillons, motifs de tachetures, effet thermique de la caméra CCD et distorsion de la lentille, erreur de non-linéarité dans le circuit de la jauge de déformation) ont fait l'objet d'une étude et de discussions. Enfin, des solutions ont été amenées afin d'aider à réduire les erreurs systématiques et aléatoires en lien avec les trois catégories de sources d'erreurs susmentionnées. Pour terminer, un nouvel algorithme DIC permettant une approximation plus juste de l'estimation initiale, entraînant par conséquent une convergence efficace et précise de l'op­timisation a été développé, programmé, mis en oeuvre et vérifié avec succès pour ce qui est des déformations importantes. La validation expérimentale a fait ressortir une erreur systé­matique inattendue des mesures DIC lorsque comparées aux mesures obtenues au moyen de la technique des jauges de déformation. Plus l'échantillon se déformait, plus l'erreur augmentait proportionnellement. Par conséquent, la distorsion graduelle des tachetures sur la surface de l'objet était probablement la cause de l'erreur. L'erreur étant systéma­tique, elle a été corrigée. Le procédé d'atomisation a permis de générer des tachetures de façon reproductible sur la surface d'un objet. Grâce aux mesures DIC, le comportement mécanique des polymères soumis à des déformations importantes, comme le polyméthyl métacrylate servant à la reconstruction du squelette, peut être étudié et une fois maîtrisé, servir à l'élaboration de matériaux plus efficaces.
Abstract : The present thesis is focused on the non-contact and efficient strain measurement using the Digital Image Correlation (DIC) method, which employs the tracking of random speckle pattern for accurate measurement of displacements on a surface of an object undergoing deformation. Specifically, a more efficient DIC algorithm was successfully developed, implemented, and validated. This thesis consists of five parts related to the novel DIC algorithm: (a) the development and implementation, (b) the numerical verification, (c) the experimental validation, for tensile loading, by comparing to the deformation measurements using the strain gauge technique, (d) the investigation of a novel atomization process to reproducibly generate the speckle pattern for accurate tracking, and (e) the analysis of the error sources in the DIC measurements. Specifically, the DIC algorithm was used to exemplarily examine the mechanical properties of polymethyl methacrylate (PMMA) used in skeletal reconstruction. In the DIC algorithm, images of an object are captured as it deforms. Nonlinear optimization techniques are then used to correlate the speckle on the surface of the objects before and after the displacement. This optimization process includes a choice of suitable initial displacement values. The more accurate the estimation of these initial displacement values are, the more likely and the more efficient the convergence of the optimization process is. The thesis introduced a novel, fuzzy logics based processing technique, approximation of the initial values of the displacement for initializing iterative optimization, which more accurately and efficiently renders the displacements and deformations as results. The mathematical formulation of the novel algorithm was developed and then successfully implemented into MATLAB programming language. The algorithmic verification was performed using computer-generated images simulating rigid body displacements and uniform tensile deformations. Specifically, the rigid motion images simulated (1) displacements of 0.1-1 pixel for the rigid body translation, (2) rotation angles of 0.5-5 ̊ for rigid body rotation and (3) large tensile deformations of 5000-300000µɛ, respectively. The verification processes showed that the accuracy of the novel DIC algorithm, for the simulated displacement types and levels above 99%. The experimental validation was conducted to examine the effectiveness of the novel technique under realistic testing conditions. Normalized PMMA specimens, in accordance to ASTM F3087, were produced, inspected and subjected to tensile loading until failure. The deformation of the specimen surface was measured using (a) the novel DIC, and (b) strain gauge rosette techniques. The mean maximum force and ultimate strength of four specimens were 882.2±108.3 N and 49.3±6.2 MPa, respectively. The mean ultimate deformation from the gauge and DIC groups were 15746±2567µɛ and 19887±3790µɛ, respectively. These large deformations are common in polymeric materials, and the DIC technique has thus far not been investigated for large deformation. The relative mean error of the DIC measurement, in reference to those of the strain gauge technique, was found to be up to 26.0±7.1%. Accordingly, the mean Young's modulus and Poisson's ratio of strain gauge measurement were 3.78±0.07 GPa and 0.374±0.02, and of the DIC measurements were 3.16±0.61 GPa and 0.373±0.08, respectively. The increasing difference of the DIC strain measurements relative to those of the strain gauge technique is likely related to the gradual distortion of the speckle pattern on the surface of the tensile specimen. Subsequently, a Correction Factor (CF) of 1.27 was introduced to correct for the systematic error in the deformation measurements of the DIC group. The corrected ultimate deformation of the DIC measurements became 15712±357µɛ with the relative mean error of -0.5±7.1%, if compared to those measurements of the strain gauge techniques. Correspondingly, the mean Young's Modulus and Poisson's ratio of the DIC and of the strain gauge measurements became 3.8±0.4 GPa and 0.368±0.025, respectively. Using an atomization process, paint speckles were reproducibly generated on the surface of an object. A factorial design of experiments was used to investigate the speckle pattern (grey value distribution and gradient) for the DIC measurement accuracy. Specifically, nine different speckle patterns were generated using the atomization process and tested for rigid body translation and rotation. The results showed the relative mean errors among the nine speckle patterns varied from 1.1±0.3% to -6.5±3.6%. The preferred speckle pattern, which was characterized by a wide range of sharp speckle and of grey values, produced a mean error of 1.1±0.3%. The analysis of errors and relating sources in the DIC measurement was conducted. Three categories of sources including algorithmic sources, processing parameters sources (subset size, number of pixels computed) and physical environment sources (specimen uniformity, speckle pattern, self-heating effect of the CCD camera and lens distortion of the camera, non-linearity error in strain gauge circuit) were investigated and discussed. Finally, the solutions were provided in order to help reduce the systematic and random errors relating to the aforementioned three categories of sources for errors. In conclusion, a novel DIC algorithm for a more accurate approximation of the initial guess and accordingly for an efficient and accurate convergence of the optimization was successfully formulated, developed, implemented and verified for relatively large deformations. The experimental validation surprisingly showed a systematic error of the DIC measurements, if compared to the measurements of the strain gauge technique. The larger the deformation applied to the specimen, the larger the error gradually became. Therefore, the gradual distortion of the speckles on the surface of the object was likely the underlying cause of the error. The error was systematic and therefore corrected. The atomization process allowed generating reproducible speckles on the surface of an object. Using the DIC measurements, the mechanical behavior of polymers, undergoing large deformations, such as polymethyl methacrylate used in skeletal reconstruction can be investigated and, once understood, the knowledge gained can help develop more effective materials.

The aorta is the largest artery in the mammal and it’s rather distensible due to its high degree of elasticity. It has a heterogeneous structure, where some of the key elements are the proteins collagen and elastin; which are essential for the mechanical properties of the aortic tissue. This thesis investigates the influence of elastase and collagenase on mechanical properties of porcine aorta. This was achieved by developing an appropriate biaxial tensile test method; which closely represents the in vivo conditions of the aortic tissue. To investigate the influence of collagen and elastin some samples were exposed to the enzymes collagenase and elastase to chemically manipulate a decomposition of the proteins in tissue. The exposed samples were tested in the developed biaxial test method and compared to native (untreated) samples. The wall samples exposed to enzymes were exposed for a varied time period of 1h, 3h and 6h. All experimental data from the mechanical tests were also used to identify model parameters of three different constitutive functions (Fung, HGO and Ogden), trying to define the differences in the results depending on type of enzyme exposure and exposure time. The results of the study show that collagenase exposed samples tends to be less distensible compared to the native samples in the circumferential direction. The longitudinal direction showed no differences between native and exposed samples, probably due to that the collagen fibers lay in the circumferential direction. The elastase exposed tissue samples tended to be more distensible than the native samples, especially for the circumferential direction. However, the results from the biaxial tests are complex and difficult to analyse. Further on additional test are necessary to achieve a deeper understanding of the results. The constitutive model results show that the anisotropic models (Fung and HGO) describe the experimental data more accurate than the isotropic model (Ogden), possibly due to that biological material is most often anisotropic. The parameter identification is not conclusive due to varied results and additional tests are desirable to reach a more statistical accuracy.

The thesis investigate the response of pile foundations subjected to axial load, with application to offshore wind turbines supported by multi-pod steel jackets. Wind turbines are relatively light weight structures as compared to other offshore structures and this results on the foundation in high tensile loadings. For this reason, the thesis focus is the response of a open ended steel pile subjected to pull out. The study develops on the results of a large-scale testing campaign recently conducted at the Test Centre of Support Structures of the Universität Hannover. The model piles encompassed various lenghts, diameters and thicknesses. In the thesis, different design methods (ICP-05, UWA-05, NGI-05 and Fugro-05) have been used to back analyse the experimental results and were compared to each others. Results of site and laboratory tests on the soil used in the experiments were also used to identify the soil parameters required to implement finite element models of the tested piles. In particular, CPT tests and triaxial tests were considered and the parameters derived are the soil behavior type, the soil unit weight, the stiffness modulus, the relative density, the poissons ratio, and the peak friction angle. Finite element analyses were then run in the experimental boundary and loading conditions e the results were compared with experimental data. A good agreement was observed, particularly on the capacity. The advantage of using the finite element method is the possibility to gain an insight in the pile behaviour and describe the entire load-displacement curve, when compared to CPT based bearing capacity prediction. Good results were achieved using a simple constitutive model, improvement can be surely gained by implementing more sophisticate soil models.

The primary objective of this research was to experimentally investigate material and bond properties of three different types of fiber reinforced polymer (FRP) bars, and determine their effect on the design of a bridge deck using FRP bars as the top mat of reinforcement. The properties evaluated include the tensile strength, modulus of elasticity, bond behavior, and maximum bond stress. The experimental program included 47 tensile tests and 42 beam end bond tests performed with FRP bars. Tensile strength of the bars from the tensile testing ranged from 529 MPa to 859 MPa. The average modulus, taken from all the testing, for each type of bar was found to range from 40 GPa to 43.7 GPa. The maximum bond stress from the beam end bond tests ranged from 9.17 MPa to 25 MPa. From the tests, design values were found in areas where the properties investigated were related. These design values include design tensile strength, design modulus of elasticity, bond coefficient for deflection calculations, bond coefficient for crack width calculations, and development length. The results and conclusions address design concerns of the different types of FRP bars as applied in the top mat of reinforcement of a bridge deck. A secondary objective was to evaluate the disparity in results between direct pullout tests, and beam end bond tests. Results from the experimentally performed beam end bond test were compared to previous literature involving the direct pullout tests. Results from the performed beam end bond tests were higher than all of the literature using direct pullout results. No recommendations were given on the disparity between the two test methods.
Master of Science

Since a large part of the hydropower structures in Sweden was built in the 1950s and 1960s, many of them are slowly but surely exhibiting deterioration. The hydropower companies are facing big challenges and are consequently investing in effective repairing methods since a hydropower structure failure could pose serious consequences and dangers to people, the environment, and the community. Many structures within hydropower are made of concrete and the demands on the new supplementing concrete are high. Concrete with the potential to meet these high demands is the pre-placed aggregate concrete, which has shown promising results regarding its mechanical properties in previous studies. For this reason, this type of concrete is of interest to investigate. The focus has not been on optimizing the pre-placed aggregate concrete for full-scale productions. Instead, the main objectives of this master thesis were to study and analyze the mechanical properties of this type of concrete, such as shrinkage, compressive strength, splitting tensile strength, freeze-thaw resistance and moreover investigate parameters of importance in the mix design to obtain a homogenous and easy flowing grout that successfully could fill the voids between the coarse aggregates. The investigations were carried out by laboratory experiments in the research and laboratory facilities of Vattenfall in Älvkarleby. The mix design of the grout was developed using the methods and requirements stated in the American Society for Testing and Materials, ASTM standards, and The Swedish Institute for Standards, SiS. A total of 15 grout-mixes were made. However, only the last five were used to cast specimens as the air content was insufficient in the first ten. The results indicated that it is necessary to replace the air-entraining admixture with microspheres in order for the pre-placed aggregate concrete to meet the requirements in exposure class XF3 and XC4. The scaling of the pre-placed aggregate concrete was less than 0.1 kg/m2 at 56 cycles, and thus, the freeze-thaw resistance was classed as very good. Moreover, the use of slag considerably reduced the bleeding of the grout and also improved the casting results. However, on the other hand, it increased the shrinkage of the pre-placed aggregate concrete. An efficiency factor of 0.6 proved to be too low since the compressive strength of the specimen with slag was approximately 50 % higher than the ones without. Furthermore, the shrinkage of the pre-placed aggregate concrete was after 63 days found to be lower than that of the conventional concrete. Also, the compressive strength of the pre-placed aggregate concrete without slag proved to be approximately 15 % lower than that of conventional concrete. Additionally, vibration during casting was found to increase the compressive strength of the pre-placed aggregate concrete and also improved the casting results. Low bleeding, combined with a high discharge time of approximately 45 seconds for 1.7 liters of grout, generated the best casting results. The results from the investigations have shown that this type of concrete has great potential. However, actions and further investigations should be made to see whether changing the fine aggregate size to a smaller one improves the ability of the grout to penetrate the voids between the coarse aggregates. Moreover, pump injection of the grout should be tested instead of pouring it over the coarse aggregates to see whether it improves the casting results and the mechanical properties.
Då en stor del av vattenkraftsdammarna i Sverige byggdes på 1950 och 1960-talet börjar många av dessa sakta men säkert brytas ner. Vattenkraftföretagen står inför stora utmaningar och investerar följaktligen i effektiva reparationsmetoder då dammbrott skulle kunna få allvarliga konsekvenser för människor, den omgivande miljön och för samhället. Flertalet konstruktioner inom vattenkraften är gjorda av betong och kraven på den nya kompletterande betongen är höga. En betong med potentialen att möta och uppfylla dessa höga krav är injekteringsbetongen som i tidigare studier uppvisat lovande resultat beträffande dess mekaniska egenskaper. Med anledning av detta är injekteringsbetongen av intresse att undersöka. Fokus har inte varit på att optimera injekteringsbetongen i syfte att genomföra fullskaliga försök. Istället har huvudsyftet med detta examensarbete varit att studera och analysera injekteringsbetongens mekaniska egenskaper såsom krympning, tryckhållfasthet, spräckhållfasthet, frostbeständighet samt undersöka viktiga parametrar i skapandet av ett homogent och lättflytande cementbruk som med god framgång kunde fylla ut hålrummen mellan grova ballasten. Undersökningarna utfördes genom laboratorieförsök på Vattenfalls betonglaboratorium i Älvkarleby. Vidare har skapandet och utvecklandet av bruket utförts i enlighet med metoder och krav angivna i American Society for Testing and Materials, ASTM standards, samt i Svenska institutet för Standarder, SiS. Totalt gjordes 15 bruksblandningar, dock användes enbart de sista fem till gjutning av provkroppar då lufthalten visade sig vara för låg i dem första tio. Resultaten indikerade på att det är nödvändigt att ersätta luftporbildare med mikrosfärer för att erhålla en lufthalt som uppfyller kraven för betong i exponeringsklass XF3 samt XC4. Injekteringbetongens avflagning efter 56 dygn var mindre än 0.1 kg/m2 och frostbeständigheten kunde därmed klassas som mycket god. Användningen av slagg minskade cementbrukets vattenseparation avsevärt och bidrog även till förbättrade gjutresultat. Dock bidrog det å andra sidan till en ökad krympning hos injekteringsbetongen. En effektivitetsfaktor på 0.6 visade sig vara för låg då injekteringsbetongen med slagg hade en cirka 50 % högre tryckhållfasthet än dem utan. Dessutom visade sig injekteringsbetongens krympning vara mindre än den konventionella betongens efter 63 dagar. Tryckhållfastheten hos injekteringsbetongen utan slagg uppvisade även en cirka 15 % lägre tryckhållfasthet än den konventionella betongens. Vibrering under gjutning visade sig höja tryckhållfastheten hos injekteringsbetongen samt förbättra gjutresultaten. En låg vattenseparation i kombination med en flödestid på cirka 45 sekunder för 1.7 liter bruk visade sig ge bästa gjutresultaten. Resultaten från laboratorieförsöken har visat på att injekteringsbetongen besitter stor potential. Dock bör ytterligare undersökningar genomföras för att bedöma huruvida en mindre ballastfraktion för sanden påverkar brukets förmåga att penetrera den grova ballasten. Vidare bör bruket pumpas in istället för att hällas över den grova ballasten, detta för att se huruvida gjutresultaten samt de mekaniska egenskaperna hos injekteringsbetongen skulle förbättras.

Buňka tvoří složitý biologický systém vystavený mnoha mimobuněčným mechanickým podnětům. Hlubší pochopení jejího mechanického chování je důležité pro charakterizaci její odezvy v podmínkách zdraví i nemoci. Výpočtové modelování může rozšířit pochopení mechaniky buňky, která může přispívat k vytvoření vztahů mezi strukturou a funkcí různých typů buněk v různých stavech. Za tímto účelem byly pomocí metody konečných prvků (MKP) vytvořeny dva bendotensegritní modely buňky v různých stavech: model vznášející se buňky pro analýzu její globální mechanické odezvy, jako je protažení nebo stlačení, a model buňky přilnuté k podložce, který vysvětluje odezvu buňky na lokální mechanické zatížení, jako třeba vtlačování hrotu při mikroskopii atomárních sil (AFM). Oba zachovávají základní principy tensegritních struktur jako je jejich předpětí a vzájemné ovlivnění mezi komponentami, ale prvky se mohou nezávisle pohybovat. Zahrnutí nedávno navržené bendotensegritní koncepce umožňuje těmto modelům brát v úvahu jak tahové, tak i ohybové namáhání mikrotubulů (MTs) a také zahrnout vlnitost intermediálních filament (IFs). Modely předpokládají, že jednotlivé složky cytoskeletu mohou měnit svůj tvar a uspořádání, aniž by při jejich odstranění došlo ke kolapsu celé buněčné struktury, a tak umožňují hodnotit mechanický příspěvek jednotlivých složek cytoskeletu k mechanice buňky. Model vznášející se buňky napodobuje realisticky odezvu síla-deformace během protahování a stlačování buňky a obě odezvy ilustrují nelineární nárůst tuhosti s růstem mechanického zatížení. Výsledky simulací ukazují, že aktinová filamenta i mikrotubuly hrají klíčovou úlohu při určování tahové odezvy buňky, zatímco k její tlakové odezvě přispívají podstatně jen aktinová filamenta. Model buňky přilnuté k podložce dává odezvu síla-hloubka vtlačení ve dvou různých místech odpovídající nelineární odezvě zjištěné experimentálně při AFM. Výsledky simulací ukazují, že pro chování buňky je rozhodující místo vtlačení a její tuhost určují aktinová povrchová vrstva, mikrotubuly a cytoplazma. Navržené modely umožňují cenný vhled do vzájemných souvislostí mechanických vlastností buněk, do mechanické úlohy komponent cytoskeletu jak individuálně, tak i ve vzájemné synergii a do deformace jádra buňky za různých podmínek mechanického zatížení. Tudíž tato práce přispívá k lepšímu pochopení mechaniky cytoskeletu zodpovědné za chování buňky, což naopak může napomáhat ve zkoumání různých patologických podmínek jako je rakovina a cévní choroby.

The design approach changed in the last decades with the innovation offered by software for Computer-Aided Design (CAD), three-dimensional computer modelling and digital fabrication methods enabling new forms. The development in digital fabrication techniques led to the application of automatic processes in the structural engineering sector through Additive Manufacturing (AM) based technologies. It offers numerous benefits over conventional manufacturing methods, such as design of more complex and optimized components due to greater freedoms in shape and geometry, therefore bringing to a reduced material usage and shortened build times. The focus of this research is on the metal additive manufacturing methods, in particular, the adopted technique is the Wire-and-Arc Additive Manufacturing (WAAM), which best suits the possibility to realize large-scale metal structures and to allow new geometric forms. WAAM advantages compared to the other processes are fast large-scale production, freedoms in shape and geometry, structural efficiency with reduced material usage. The current research comprises the overarching process from the computational design to the mechanical characterization of the WAAM-produced elements, through the fabrication step. The computational design and fabrication stages were carried out at Technische Universität Braunschweig. There is still limited research focused on the characterization of WAAM-produced metal elements for structural engineering applications, therefore the research carried out at University of Bologna was focused on the establishment of 3D-outcome mechanical properties, pointing up the influence of surface roughness and imperfections on the mechanical response, together with the study on how the intersection between WAAM-produced bars influences the overall behavior of the specimen.

This study attempts to further our knowledge of fracture behaviour by establishing an experimental system that links tensile strength, fracture initiation and propagation of an anisotropic rock (Mancos Shale) using an integrated Brazilian Test Setup equipped with Acoustic Emission and High Speed Video. The unique experimental conguration was applied to an anisotropic gas shale (Mancos Shale) in addition to other petroleum related reservoir rocks (such as sandstone and chalk). The variation in tensile strength, fracture initiation location, propagation time and the failure pattern are examined as a function between the layer plane and the loading direction. A time shift was shown to exist between the time at ultimate tensile stress and the time at fracture initiation. This phenomenon has been dubbed the Naet Shift.

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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2004.
Collard, David, Committee Co-Chair ; Schiraldi, David, Committee Member ; Liotta, Charles, Committee Member ; Weck, Marcus, Committee Member ; Srinivasarao, Mohan, Committee Member ; Kumar, Satish, Committee Co-Chair. Vita. Includes bibliographical references.

The present Master thesis deals with location of aluminium castings in the heat treatment furnace and its influence on mechanical properties. As testing samples for the experimental part, tensile bars were used; they were cast from the subeutetic silumin AlSi7Mg0,6. These samples were placed in the furnace in the locations where temperatures were calibrated by the furnace supplier. Then, tensile tests were performed to evaluate the resulting mechanical properties of the samples. The experiment was carried out in the foundry of non-ferrous metals, MESIT foundry Ltd., Uherské Hradiště.

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O bambu é uma planta renovável, perene, tropical e que apresenta uma série de vantagens, tais como: crescimento rápido, elevada resistência mecânica, grande versatilidade, beleza, e não necessita do replantio de colmos. Certamente, fica evidente que o bambu é um material de grande potencial, para diversos setores, sobretudo da construção civil, em que o mesmo vem sendo utilizado desde os tempos mais remotos. Nas estruturas de concreto, o bambu tem sido estudado como um elemento passível de resistir aos esforços de tração. Entretanto, como desvantagens, o bambu é um material orgânico e higroscópico. Após a concretagem, durante a cura do concreto, o bambu absorve água e, consequentemente, tem suas dimensões aumentadas. Com o concreto endurecido, o bambu começa a perder a água absorvida e se retrai, sofrendo uma redução de seu volume, o que diminui a eficiência da aderência entre os materiais. Outra desvantagem do bambu é a região do nó, cuja resistência à tração é muito inferior à da região internodal. O presente trabalho tem como principal objetivo avaliar o comportamento estrutural de vigas de concreto armado, sem e com reforço adicional de taliscas de bambu, por meio de ensaios de flexão. As taliscas de bambu utilizadas como reforço adicional à armadura são de dois tipos: com e sem reforços nas regiões nodais. Com o intuito de analisar a condição de aderência entre a talisca de bambu e o concreto, foram realizados ensaios de arrancamento. As taliscas foram elaboradas a partir de colmos da espécie Bambusa vulgaris, disponível na cidade de Ilha Solteira, algumas com e outras sem reforços nas regiões nodais. Todas as taliscas foram impermeabilizadas com látex de seringueira. Para a colagem dos reforços nos nós das taliscas, foi utilizada uma resina poliuretana bicomponente à base de óleo de mamona. As taliscas com reforços colados apresentaram um aumento da resistência à tração. Com relação ao ensaio de arrancamento, a existência do reforço nos nós permitiu acréscimos em relação à tensão normal, provocando a ruptura da talisca e não o seu escorregamento. Quanto ao ensaio de flexão das vigas, concluiu-se que a presença das taliscas de bambu aumentou a capacidade resistente das vigas e, portanto, poderia se pensar na redução da quantidade de aço a ser utilizado. O reforço nos nós das taliscas de bambu proporcionou um melhor comportamento com relação às flechas e um discreto aumento na capacidade resistente das vigas. No que diz respeito ao padrão de fissuração, observou-se que a ruptura das vigas ocorreu na região central, região submetida aos maiores momentos fletores, e, embora as vigas com reforço adicional de taliscas de bambu reforçadas nos nós tenham apresentado maior número de fissuras, aparentemente, o padrão de fissuração foi basicamente o mesmo para todas as vigas ensaiadas.
Bamboo is a renewable, perennial and tropical plant, and that presents a number of advantages, such as: growth quickly, high mechanical resistance, versatility, beauty, and does not require the replanting of culms. Certainly it is clear that bamboo is a great potential material for various industries, especially construction, in which it has been used since ancient times. In concrete structures, bamboo has been studied as an element capable of resisting the traction efforts. However, as disadvantages, bamboo is an organic and hygroscopic material. After the concrete, during curing of the concrete, bamboo absorbs water and, therefore, has increased their dimensions. With the hardened concrete, bamboo begins to lose water absorbed and retracts suffering a reduction of its volume, which decreases the efficiency of adhesion between the materials. Another disadvantage of bamboo is the node region, whose tensile strength is much lower than the internode region. This study has as main objective to evaluate the structural behavior of reinforced concrete beams, with and without additional reinforcement bamboo splints through bending tests. The bamboo splints used as additional reinforcement to armor are of two types: with and without reinforcements in the node regions. In order to examine the condition of adhesion between the concrete and bamboo splint pull out tests were done. The splints were prepared from culms of Bambusa vulgaris species, available in the city of Ilha Solteira, some with and some without reinforcements in the node regions. All splints were coated with rubber trees latex. For bonding reinforcements in nodes of splints, we used a two-component polyurethane resin oil-based of castor plant. Samples with glued reinforcements showed an increase in the tensile strength. Regarding the pull out test, the existence of reinforcement in the nodes allowed increases in relation to normal tension, causing the rupture of splint and not its slipping. As for the bending test of the beams, it is concluded that the presence of bamboo splints increased bearing capacity of the beams and, therefore, could think of reducing the amount of steel to be used. Strengthening the nodes of bamboo splints provide better performance with respect to deflections and a slight increase in resitente capacity of beams. With regard to the crack pattern, it was observed that the breakage of the beams occurred in the central region, region subjected to higher bending moments, and, although the beams with additional reinforcement bamboo splints reinforced in the nodes had a higher number of cracks, apparently, the crack pattern was essentially the same for all tested beams.

Orientador: José Luiz Pinheiro Melges
Resumo: O bambu é uma planta renovável, perene, tropical e que apresenta uma série de vantagens, tais como: crescimento rápido, elevada resistência mecânica, grande versatilidade, beleza, e não necessita do replantio de colmos. Certamente, fica evidente que o bambu é um material de grande potencial, para diversos setores, sobretudo da construção civil, em que o mesmo vem sendo utilizado desde os tempos mais remotos. Nas estruturas de concreto, o bambu tem sido estudado como um elemento passível de resistir aos esforços de tração. Entretanto, como desvantagens, o bambu é um material orgânico e higroscópico. Após a concretagem, durante a cura do concreto, o bambu absorve água e, consequentemente, tem suas dimensões aumentadas. Com o concreto endurecido, o bambu começa a perder a água absorvida e se retrai, sofrendo uma redução de seu volume, o que diminui a eficiência da aderência entre os materiais. Outra desvantagem do bambu é a região do nó, cuja resistência à tração é muito inferior à da região internodal. O presente trabalho tem como principal objetivo avaliar o comportamento estrutural de vigas de concreto armado, sem e com reforço adicional de taliscas de bambu, por meio de ensaios de flexão. As taliscas de bambu utilizadas como reforço adicional à armadura são de dois tipos: com e sem reforços nas regiões nodais. Com o intuito de analisar a condição de aderência entre a talisca de bambu e o concreto, foram realizados ensaios de arrancamento. As taliscas foram elaboradas a parti... (Resumo completo, clicar acesso eletrônico abaixo)
Mestre

A Comparison Study of Composite Laminated Plates with Holes under Tension A study was conducted to quantify the accuracy of numerical approximations to deem sufficiency in validating structural composite design, thus minimizing, or even eliminating the need for experimental test. Error values for stress and strain were compared between Finite Element Analysis (FEA) and analytical (Classical Laminated Plate Theory), and FEA and experimental tensile test for two composite plate designs under tension: a cross-ply composite plate design of [(0/90)4]s, and a quasi-isotropic layup design of [02/+45/-45/902]s, each with a single, centered hole of 1/8” diameter, and 1/4" diameter (four sets total). The intent of adding variability to the ply sequences and hole configurations was to gauge the sensitivity and confidence of the FEA results and to study whether introducing enough variability would, indeed, produce greater discrepancies between numerical and experimental results, thus necessitating a physical test. A shell element numerical approximation method through ABAQUS was used for the FEA. Mitsubishi Rayon Carbon Fiber and Composites (formerly Newport Composites) unidirectional pre-preg NCT301-2G150/108 was utilized for manufacturing—which was conducted and tested to conform to ASTM D3039/D3039M standards. A global seed size of 0.020, or a node count on the order of magnitude of 30,000 nodes per substrate, was utilized for its sub-3% error with efficiency in run-time. The average error rate for FEA strain from analytical strain at a point load of 1000lbf was 2%, while the FEA-to-experimental strains averaged an error of 4%; FEA-to-analytical and FEA-to-tensile test stress values at 1000lbf point load both averaged an error value of 6%. Suffice to say, many of these strain values were accurate up to ten-thousandths and hundred-thousandths of an in/in, and the larger stress/strain errors between FEA and test may have been attributed to the natural variables introduced from conducting a tensile test: strain gauge application methods, tolerance stacks from load cells and strain gauge readings. Despite the variables, it was determined that numerical analysis could, indeed, replace experimental testing. It was observed through this thesis that a denser, more intricate mesh design could provide a greater level of accuracy for numerical solutions, which proves the notion that if lower error rates were necessitated, continued research with a more powerful processor should be able to provide the granularity and accuracy in output that would further minimize error rates between FEA and experimental. Additionally, design margins and factors of safety would generally cover the error rates expected from numerical analysis. Future work may involve utilizing different types of pre-preg and further varied hole dimensions to better understand how the FEA correlates with analytical and tensile test results. Other load types, such as bending, may also provide insight into how these materials behave under loading, thus furthering the conversation of whether numerical approximations may one day replace testing all together.

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The aim of this study was to characterize the mechanical properties of the fiber and taquaralixa (Merostachys sp.) composites with polyester and epoxy matrixes by means of tensile, pull out and flexural tests. Initially, the stalks of taquara went through a drying process to determine the moisture content. Afterwards, the taquara sticks were chemically treated with a solution of sodium hydroxide 10% w/w and hydrogen peroxide 10% v/v, causing softening of the sticks that later were crushed with a rolling machine, in order to partially remove lignin and separate the fibers. To determine the tensile strength of the fiber, tensile tests were performed. And fiber was tested by means of pull out test for determining the shear stress and critical length in the polyester and epoxy matrixes. An optic microscope and an application software were used to determine the cross-sectional area and the perimeter of the fiber. Composites with long fibers and matrixes of polyester and epoxy were prepared through the compression molding process. The fiber concentrations used in the polyester matrix were: 40, 60, 70 and 75% w/w; and for the epoxy matrix 40, 60 and 75% w/w of fiber were used. Composites with random and short fibers were produced with epoxy matrix. Fibers with 13 mm in length were used at the concentrations of 50 and 60% w/w; fibers with 25 mm in length at concentrations of 50 and 60% w/w and fibers with 60 mm in length at a concentration of 50% w/w. Flexural tests were performed for the composites and it was possible to determine the flexural stress, Young s Modulus, strain and density for each specimen. From the results of the long fibers composites and using the values of tensile and strain within the linear region, the Young s modulus of the fiber was estimated through interpolation of the rule of mixtures lower limit and Halpin-Tsai equations. For the results of composites with random and short fibers together with the results of composites with long fibers and epoxy matrix, the rule of mixtures lower limit equation was interpolated in order to obtain an estimate of the Young s modulus or tensile strength in function of the volumetric fraction and fiber length. With the results of tensile strength, Young s modulus and density, it was possible to perform a comparison among the mechanical properties of wood Angicovermelho (Anadenanthera peregrina), Peróba-rosa (Aspidosperma polyneuron), Piquiá (Caryocar villosum) and Eucalipto (Eucalyptus Grandis and Citriodora). Composites with long fibers and composites with 60 mm in lenght of fibers presented superior properties in comparison to these woods.
Este trabalho teve como objetivo caracterizar as propriedades mecânicas da fibra e os compósitos de fibra de taquara-lixa (Merostachys sp.) com matriz poliéster e epóxi por meio de ensaios de tração, pull out e flexão de três pontos. Inicialmente, os colmos da taquara passaram por um processo de secagem para a determinação do teor de umidade. Em seguida, os gravetos da taquara foram tratados quimicamente com solução de hidróxido de sódio a 10% m/m e peróxido de hidrogênio a 10% v/v que provocou o amolecimento dos gravetos que na sequência foram esmagados com auxílio de uma calandra, com o objetivo de retirar parcialmente a lignina e separar as fibras. Os ensaios de tração da fibra foram realizados para a determinação da tensão de ruptura. E ensaios de pull out da fibra foram realizados para a determinação da tensão cisalhante de ruptura e comprimento crítico nas matrizes poliéster e epóxi. Para a determinação da área transversal e perímetro da fibra foi utilizado um microscópio óptico e um aplicativo de tratamento de imagem. Compósitos com fibras longas e matrizes de poliéster e epóxi foram confeccionados por meio do processo de moldagem por compressão. As concentrações de fibras utilizadas para a matriz poliéster foram 40, 60, 70 e 75% m/m e para a matriz epóxi foram 40, 60 e 75% m/m. Compósitos com fibras curtas e aleatórias também foram produzidos com matriz epóxi. Foram utilizadas fibras com 13 mm de comprimento nas concentrações de 50 e 60% m/m de fibra, 25 mm de comprimento nas concentrações de 50 e 60% m/m e 60 mm de comprimento na concentração de 50% m/m. Ensaios de flexão de 3 pontos foram realizados para os compósitos, e determinou-se a tensão de flexão, o módulo de elasticidade, a deformação e a massa específica para cada corpo de prova. A partir dos resultados obtidos dos compósitos com fibras longas e utilizando-se os valores de tensão e deformação dentro do regime linear, foi possível estimar o módulo de elasticidade da fibra por meio da interpolação das equações da regra das misturas limite inferior e equação de Halpin-Tsai. Para os resultados dos compósitos com fibras curtas e aleatórias juntamente com os resultados dos compósitos com fibras longas e matriz epóxi foi interpolada a equação da regra das misturas limite inferior com o objetivo de obter uma estimativa do módulo de elasticidade ou da tensão de flexão em função da fração volumétrica, e comprimento da fibra. Com os resultados de tensão de flexão, módulo de elasticidade e massa específica foi possível realizar uma comparação em relação as propriedades mecânicas das madeiras Angico-vermelho (Anadenanthera peregrina), Peróba-rosa (Aspidosperma Polyneuron), Piquiá (Caryocar villosum) e Eucalipto (Eucaliptus Citriodora e Grandis). Os compósitos com fibras longas e fibras curtas de 60 mm apresentaram propriedades superiores em comparação com estas madeiras.

L’un des principaux enjeux des acteurs aéronautiques est l’allègement des structures afin de réduire la consommation de carburant et donc les coûts de fonctionnement. A cette fin, les alliages de titane sont de plus en plus utilisés du fait de leurs très bonnes propriétés mécaniques notamment à hautes températures, pour une densité relativement faible. C’est dans ce contexte que s’inscrivent les travaux de cette thèse. L’alliage étudié est le Ti-21S, utilisé actuellement dans la fabrication des systèmes d’éjection des gaz des moteurs d’avions. La problématique de la thèse est d’évaluer les potentialités du Ti-21S, au-delà des limites conventionnelles. Pour cela, des vieillissements thermiques sous air à différentes températures (450°C - 700°C) pendant diverses durées (500h - 10000h) sont réalisés. La microstructure avant et après vieillissement est caractérisée afin de déterminer l’impact du vieillissement thermique. Ces observations montrent que les évolutions microstructurales sont directement liées à la température de vieillissement, et l’impact de la durée de vieillissement n’est pas identique pour toutes les températures de vieillissement. L’enjeu suivant de cette thèse est d’étudier le comportement mécanique en traction et en fatigue à température ambiante et à 550°C après vieillissement. Le comportement mécanique en traction est très dépendant des conditions de traitement thermique, et de ce fait de la microstructure de l’alliage. De plus, les comportements mécaniques sont également très dépendants de la température d’essai. Un autre enjeu est la compréhension des phénomènes d’oxydation sur cette plage de températures de vieillissement. La diffusion de l’oxygène dans le matériau entraîne des modifications microstructurales en proche surface, et impacte fortement la tenue mécanique de l’alliage en fragilisant le matériau. Un lien entre paramètres microstructuraux et teneur en oxygène a été mis en évidence. De même, la résistance mécanique en traction a été reliée à la microstructure
One of the main issues of the aeronautic industry is to decrease the weight of structures in order to reduce fuel consumption. Titanium alloys are more and more used due to their good mechanical properties at high temperatures, with a low density. Ti-21S, currently used in the manufacturing of nozzles, was investigated. The aim of this work is to study the potential of this alloy beyond conventional limits. Thermal treatments on air are carried out at different temperatures (450°C - 700°C) for various durations (500h - 10000h). The microstructure is characterized before and after aging in order to determine the impact of aging thermal. The observations show that microstructural evolutions are related to aging temperature, and impact of time aging is not the same for all temperatures. Another aim is to study the mechanical behavior with tensile and fatigue tests at room temperature and 550°C after aging. Mechanical tensile behavior depends on the aging temperature and the microstructure of the alloy. Moreover, mechanical behavior depends on test temperature. Another issue is the understanding of oxidation phenomena over the range of temperatures, and to determine the effects of oxidation on both microstructure and mechanical behavior. The diffusion of oxygen in the material leads to the microstructural evolution near the surface, and impacts mechanical strength by weakening the material. A link between microstructure and oxygen content is demonstrated. Similarly, the tensile strength is connected to microstructure

Hybrid composites play a key role in sustainable development. For many years, carbon fibres in an epoxy matrix have been an attractive option for many structural applications because of their higher specific mechanical properties mostly. However, recycling and sustainability are some of the composite shortcomings; and in that context, natural fibres have gained popularity.  The present study aimed to design and manufacture short carbon/flax hybrid composites. Two different arrangements were chosen: random and layers configuration. Resin Transfer Moulding (RTM) was used to fabricate these hybrid composites. Mechanical tests and optical microscopy technique were conducted to understand the effect of the interaction of these two different reinforcements. Mechanical tests showed a remarkable difference between the hybrid configurations under flexural loadings. Furthermore, outstanding property values were observed in the hybrid configurations compared to single fibre composites. The resultant materials have seemed an attractive combination of fibres with a remarkable balance between mechanical performance and eco-friendliness.

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O objetivo deste trabalho foi estudar o comportamento mecânico de cilindros de compósito polimérico reforçado com fibras. Para isso, foram produzidos cilindros com extremidades abertas reforçados com fibra de basalto e fibra de vidro, utilizando a técnica de enrolamento filamentar (filament winding). Estes cilindros foram submetidos a ensaio hidrostático com carregamento circunferencial, ensaio de ruptura de anel (split disk test) e ensaio de resistência ao cisalhamento interlaminar (ILSS). Uma placa do compósito de fibra de basalto foi produzida por enrolamento filamentar, para caracterização por ensaio de resistência à tração. Todos cilindros submetidos ao ensaio hidrostático apresentaram fratura localizada em uma faixa de altura do cilindro, com extensas delaminações das camadas circunferenciais. Os compósitos epóxi/fibra de basalto superaram ou igualaram os de compósito epóxi/fibra de vidro nas comparações entre resultados dos valores das propriedades mecânicas avaliadas, nas porcentagens: resistência à tração aparente de ruptura de anel em 45% e 43% em resistência específica; ILSS, em 11%; resistência/tensão de membrana de ruptura no ensaio hidrostático, em 55%.
Dissertação (Mestrado em Tecnologia Nuclear)
IPEN/D
Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

One of the major health problems in western societies is back pain, with a prevalence rate of 49%–80%. In many cases, the back pain is due to degenerated discs. The gold standard to treat a severely degenerated disc is spinal fusion, where the vertebral disc is replaced with a cage structure. However, fusion cages have a failure rate of 30%, hence the need for further development. The focus of this thesis is to evaluate the combination of calcium phosphate cement with titanium, for a spinal application. Mechanical tests in the form of tensile, compression and 4-point-bending were performed to study the different material properties. The obtained results was applied as material parameters for isotropic linear elastic material models, using ANSYS. This was then used to develop a cage design through topology optimisation which was further evaluated by using Finite Element Analysis. From the tensile testing of the titanium, isotropic behaviour was found. It was also found that a longer mixing time of the cement resulted in poorer mechanical properties of the calcium phosphate, however, no conclusive results were obtained from the 4-point-bending tests. The final cage geometry filled with calcium phosphate was tested under compression to see whether the cage could protect the calcium phosphate or not. MicroCT after the test confirmed that no larger cracks developed during the testing, suggesting that the cage is strong enough to protect the calcium phosphate from mechanical failure.

Dans le domaine de la métallurgie, la fabrication additive (FA) est un procédé de mise en forme des matériaux en pleine expansion dans plusieurs secteurs industriels tels que l’aéronautique, le spatial et l’automobile. L’exploitation des procédés de FA pour des applications dans l’industrie nucléaire est actuellement en cours d’étude dans différents pays. La FA permet d’élaborer des pièces optimisées avec des géométries complexes impossibles à réaliser avec les procédés conventionnels. Dans ce cadre, les travaux réalisés au cours de cette thèse visent à déterminer l’apport potentiel des procédés de FA pour la réalisation de composants métalliques pour diverses applications nucléaires dont les futurs réacteurs de Génération IV. Cette thèse présente les propriétés microstructurales et mécaniques de pièces en acier inoxydable 316L réalisées par procédé de fusion laser sélective sur lit de poudre (SLM, Selective Laser Melting). Trois thématiques ont été abordées dans cette étude : les paramètres du procédé SLM, les caractéristiques de la poudre et deux post-traitements thermiques (700°C-1h et compression isostatique à chaud : 1100°C-3h sous 1800 Bar). Leurs effets sur la microstructure et les propriétés mécaniques ont été analysés. Les propriétés en traction sur des éprouvettes en acier 316L ont été mesurées et comparées à celles d’un acier 316L forgé décrit par la norme RCC-MRX utilisée dans le domaine du nucléaire. Les résultats obtenus sont supérieurs à ceux de la norme et comparables à ceux d’un acier forgé. Cette thèse a permis de mieux cerner les interactions entre les paramètres liés au procédé, la microstructure et les propriétés mécaniques
Additive Manufacturing (AM) recently became an attractive manufacturing process in several industrial fields such as aeronautics, aerospace and automotive. The exploitation of AM processes for the nuclear industry is currently being studied in different countries. The AM enables the creation of optimized parts with complex geometries impossible to manufacture with conventional processes. This thesis aims to determine the potential contribution of AM processes for the production of metal components for various nuclear applications including future Generation IV reactors. First, the microstructural and mechanical properties of 316L stainless steel parts built by Selective Laser Melting (SLM) process are presented. Three thematics were assessed in this study: the SLM process parameters, the powder characteristics and two post heat treatments (700 ° C-1h and hot isostatic pressing: 1100 ° C-3h under 1800 Bar). Their effects on microstructure and mechanical properties were analyzed. Tensile properties of 316L steel specimens were measured and compared to those of forged 316L steel described in the nuclear field by RCC-MRX standards. The results obtained are superior to those of the standard and comparable to those of a forged steel. This thesis contributes to a better understanding of interactions between the process parameters, the microstructure and the mechanical properties

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Este trabalho apresenta um estudo prático da aplicação do conceito Leak Before Break (LBB), usualmente aplicado em usinas nucleares, em uma tubulação fabricada a partir de aço AISI 316LN soldada com a utilização de eletrodo revestido AISI 316L. O LBB é um critério fundamentado em análises de mecânica da fratura, que considera que um vazamento proveniente de uma trinca, presente em uma tubulação, possa ser detectado por sistemas de detecção de vazamento, antes que esta trinca alcance um tamanho crítico que implique na falha da tubulação. Na tubulação estudada, foram realizados ensaios mecânicos de tração e análises de Ramberg-Osgood, bem como ensaios de tenacidade à fratura para a obtenção da curva de resistência J-R do material. Os ensaios foram realizados considerando o metal base, a solda e a zona termicamente afetada (ZTA), nas temperaturas de operação de uma planta nuclear. Para as propriedades mecânicas encontradas nos ensaios foram realizadas análises de carga limite para se determinar o tamanho da trinca que cause um vazamento detectável e, também, o seu tamanho crítico que cause a falha por colapso plástico. Para o tamanho crítico de trinca encontrado na solda, região que apresentou a menor tenacidade, foram realizadas análises de Integral J e de módulo de rasgamento T, considerando falha por rasgamento dúctil. Os resultados demonstram um comportamento bem definido entre o metal base, a ZTA e a solda, onde o metal base apresenta um comportamento altamente tenaz, a solda um comportamento pouco tenaz e a ZTA apresentou propriedades mecânicas intermediárias entre o metal base e a solda. Utilizando o software PICEP, foram determinadas as curvas de taxa de vazamento versus tamanho de trinca e também o tamanho crítico da trinca, considerando análise por carga limite. Observou-se que, após certo tamanho de trinca, a taxa de vazamento do metal base é muito maior do que para a ZTA e solda, para um mesmo comprimento de trinca. Isso ocorre porque é esperado que a trinca cresça de forma mais arredondada no metal base, devido à sua maior tenacidade. O menor tamanho crítico de trinca foi encontrado para o metal base para trincas circunferenciais. Para as análises de Integral J realizadas na solda, foi demonstrado que a falha por rasgamento dúctil não ocorrerá nas condições consideradas e essa hipótese foi sedimentada pela análise de mecânica da fratura elasto-plástica (MFEL) com o uso do diagrama J/T. Dessa forma, pode-se concluir que a tubulação estudada estaria apta a ser empregada em um circuito primário de um reator que utilizasse o critério de LBB, nas condições de carregamento e geometria consideradas. Adicionalmente, concluiu-se que nessas condições apenas o modo de falha por colapso plástico é esperado.
Dissertação (Mestrado em Tecnologia Nuclear)
IPEN/D
Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

A testing system MTS Tytron 250 with an original construction was bought at the Institute of Physics of Materials, AVCR v.v.i. The main aim of this diploma thesis was to obtain experiences with the controlling of the system and with its advantages and limitations. The tensile tests were performed on Al fibres with diameters of 125 micrometer, 180 micrometer a 500 micrometer, nylon fibres of 250 micrometer and 500 micrometer and tensile and cyclic tests on Al foil of 77 micrometer in thickness. It was found that the machine is suitable for testing of either subtle specimens with low loading forces or specimens with low stiffness as e.g. polymers or very long metallic or ceramic fibres. On the other side, the Tytrom system is not able to perform tests on specimens with a high stiffness and high loading forces. Material parameters were determined with a high reproducibility. Advantages and limitations of several types of subtle specimen's fixation into the grips were studied too.

Assunto cada vez mais em pauta nos foros nacionais e internacionais e nas comunidades ao redor do mundo, a questão ambiental tem sido a grande responsável pela geração de produtos novos. A construção de obras de infraestrutura é um dos maiores consumidores de recursos naturais, gerando uma enorme quantidade de resíduos, acaba também por ser um setor causador do impacto ambiental. Tais resíduos, se descartados de maneira incorreta geram problemas ambientais, em contraponto o descarte em aterros sanitários tem um custo bastante elevado. Partindo dessas premissas, buscar a utilização de resíduos como matéria prima para a indústria da construção de obras de infraestrutura é o objetivo global desta pesquisa, visando benefícios ambientais e econômicos. Para tal, foram utilizados a cinza volante, obtida através da queima do carvão nas termelétricas e rica em sílica e alumina e a cal de carbureto, oriunda da produção do gás acetileno e que possui grande quantidade de óxido de cálcio. Através de ensaios de laboratório, busca-se nesta pesquisa avaliar a influência da quantidade de cal e da porosidade, isoladamente, na durabilidade, resistência à tração e resistência à compressão e a relação resistência à tração/resistência à compressão, objetiva-se ainda avaliar a utilização do parâmetro porosidade/teor volumétrico de cal na estimativa de resistência e verificar a existência de uma relação única para este parâmetro versus a perda de massa acumulada/número de ciclos. Para isto, foram escolhidos os pesos específicos aparentes secos de 10,6, 11,6 e 12,6 kN/m³ com os respectivos teores de umidade de 36,6%, 31,3% e 25 %, sendo os teores de cal de carbureto adotados de 5, 8 e 11%. Todas as amostras foram curadas por um período de 28 dias em câmara úmida a 23°C. Os resultados apontam que o incremento da quantidade de cal e do peso específico aparente seco provocam aumentos na resistência à tração por compressão diametral, na resistência à compressão simples e na durabilidade da mistura. A utilização de um expoente como ajuste para a relação porosidade/teor volumétrico de cal [η/( ) , ] apresentou-se adequada para a formulação de equações para a previsão da resistência do material cimentado e para a estimativa da perda de massa acumulada/número de ciclos. Além disso, a existência de relações únicas para o controle da resistência à tração na compressão diametral e da resistência à compressão simples em função da porosidade e teor volumétrico de cal mostraram-se úteis para as formulações de dosagem.
The environmental issue is increasingly been responsible for the generation of new products. Infrastructure construction is one of the largest consumers of natural resources. Looking for the use of industrial residues as material for the construction industry is the overall objective of this research, aiming at environmental and economic benefits. For this, present study has used fly ash (obtained by burning coal in thermoelectric power plants) and carbide lime (originated from the production of acetylene gas) to fabricate a novel material. Through laboratory tests, one aim in this research was to evaluate the influence of the amount of lime and porosity of the blend on durability, splitting tensile strength and unconfined compressive strength, as well as on tensile/compressive ratio. Another objective was to further evaluate the use of the porosity/lime index in the estimation of strength and checking for a unique relationship for this parameter versus accumulated loss of mass/number of cycles. For such study were chosen dry unit weights of 10.6 kN/m³, 11.6 kN/m³ and 12.6 kN/m³ with the respective moisture contents of 36.6%, 31.3% and 25.0% and carbide lime contents of 5%, 8% and 11%. All samples were cured for a period 28 days in a moist chamber at 23°C. The results show that increasing dry unit weight and the amount of carbide lime cause increases in durability and splitting tensile and unconfined compressive strength of the studied blends. The use of an exponent as an adjustment to the porosity/lime index [η/( ) . ] showed to be appropriate for formulating equations for predicting the strength of cemented material and to estimate the accumulated loss of mass/number of cycles. Furthermore, the existence of unique relationships for the control of splitting tensile tests and unconfined compression strength as a function of porosity and volumetric lime content proved useful for the dosage formulations.

La conception de moteurs aéronautiques plus performants soumet les alliages de titane constitutifs des mâts-réacteurs à des contraintes thermiques et mécaniques plus sévères. Ces matériaux doivent d’une part être qualifiés en termes de tolérance aux dommages. D’autre part, l’exposition prolongée de ces alliages de titane à des températures élevées en service pose la question de leur vieillissement métallurgique. Le dimensionnement et la maintenance de telles aérostructures doit ainsi prendre en compte l’ensemble de ces deux problématiques cruciales.Dans ces travaux, le comportement cyclique ainsi que la résistance à la fissuration par fatigue d’alliages de titane de différentes nuances (TA6V, Ti 6242 et Ti 17) et de différentes microstructures, ont été étudiés en fonction du degré de vieillissement. L’effet du vieillissement se traduit essentiellement par une augmentation des vitesses de propagation à forte valeur du facteur d’intensité de contrainte, à température ambiante. Dans un second temps, une démarche de caractérisation poussée de ce phénomène mettant en œuvre des sollicitations variées, à différentes échelles et associées à des analyses fractographiques a été appliquée. Ceci a permis de proposer un scénario d’endommagement avant et après vieillissement pour l’alliage le plus affecté par l’exposition en température, le Ti 17. Ce scénario montre après vieillissement l’apparition d’un mode d’endommagement « statique » en lien avec un processus de rupture puis décohésion intralamellaire, sans modification notable du comportement cyclique. Enfin, une approche d’équivalence temps-température est proposée pour décrire la cinétique de dégradation des propriétés mécaniques consécutive au vieillissement
The conception of more efficient aircraft engines induces increased stress and temperature levels on the titanium alloys constitutive of the engine pylon. On the one hand, these materials have to be qualified in terms of damage tolerance. On the other hand, the long term high temperature exposure of these titanium alloys gives also rise to the question of thermal aging and metallurgical stability. Hence, the dimensioning as well as the maintenance of such aerostructures need to be considered in the light of both these critical issues.In the present work, the cyclic behavior as well as the fatigue crack resistance of different titanium alloys (TA6V, Ti 6242 et Ti 17), with various microstructures were studied after different aging conditions. Aging induces mainly an increase in crack growth rates at high values of the stress intensity factor, at room temperature. Subsequently, a thorough characterization procedure of this phenomenon was undertaken,including various types of loadings, at different scales and associated with fractographic analyses. The results allowed to suggest a damage scenario before and after aging, in the case of the alloy most affected by aging: theTi 17 alloy. This scenario shows the occurrence of a « static » mode of failure, which is linked to a damage process associated with intralamellar fracture and decohesion, without noticeable changes in the cyclic behavior. Finally, a time-temperature equivalency approach was developed to describe the kinetics of degradation of the mechanical properties induced by aging

Devido à fragilidade do concreto, o controle e combate da fissuração são de importância fundamental em estruturas de concreto armado. Uma maneira de melhorar as propriedades do concreto à tração é pelo emprego de fibras. A presente pesquisa é uma tentativa de fornecer diretrizes para o dimensionamento de estruturas de concreto armado com fibras, e armadura convencional sob condições de serviço. Apresenta-se inicialmente, um estudo do comportamento do material à tração. Um modelo probabilístico/micro-mecânico fundamentado na mecânica de fratura, e capaz de prever o comportamento pós-fissuração do compósito é apresentado. O modelo prevê a relação tensão-abertura de fissura do compósito levando em conta os seguintes micro-mecanismos: travejamento de agregado e fibras, a ruptura das fibras, os efeitos de: atrito local (snubbing effect), esmagamento da matriz, Cook-Gordon, e da pré-tração das fibras. Em nível estrutural, dois modelos macro-mecânicos são apresentados. O primeiro modelo tem premissa na teoria clássica de fissura, e o segundo na mecânica de dado. O primeiro modelo é ajustado para aplicação na previsão de espaçamento e aberturas de fissura em estruturas de concreto armado com fibras discretas e aleatoriamente dispostas. É demostrado que o modelo micro-mecânico pode alimentar perfeitamente o modelo macro-mecânico. Ensaios de tração com elementos de placas de argamassa com fibras armada com tela ou fios foram realizados. Os resultados teóricos previstos pelo modelo foram comparados com os obtidos do programa experimental, e mostram uma boa concordância, comprovando a validade do modelo apresentado.
Due to the brittleness of concrete, the control and prevention of cracking in reinforced concrete structures are of prime importance. One way of improving the tensile properties of concrete is by the addition of fibres. The present research is a trial to provide guidelines for the design of fibre reinforced concrete structures under service loads. First of all, a study of the tensile behaviour of the composite material is presented. A probabilistic/fracture mechanics based micromechanical model, capable of predicting the poscracking behaviour of the material is presented. The model predicts the tensile stress-crack width relationship, accounting for the following micromechanisms: fibre and aggregate bridging, fibre rupture, local snubbing, matrix spalling, the Cook-Gordon interface effect, and fibre prestressing. At the structural level, two macromechanical models are presented. One is founded on the classical theory of cracking, while the other, a shear lag model, is founded on the continuum damage mechanics. The first model is adjusted for application to the prevision of crack width and crack spacing in fibre reinforced concrete structures with short discrete and randomly dispersed fibres. It is shown that the micromechanical model fits very well in the macrostructural model. Tensile tests with mortar specimens reinforced with continuous steel wires or meshes and PVA or polypropylene fibres were carried out. The theoretical results predicted by the model were compared with results obtained from the experimental program, and show very good agreement, confirming the validity of the theoretical model.

Desiccation-induced soil cracking is of significant interest in several engineering disciplines, which include geotechnical and geoenvironmental engineering, mining engineering, and agriculture engineering. The hydraulic, mechanical, thermal and other physico-chemical properties of unsaturated soils can be predominantly influenced due to cracks. Reliable information of these properties is required for the rational design and maintenance of earth structures taking account of the influence the soil-atmosphere interactions (e.g., for expansive soil slopes, earth dams, and embankments). In spite of significant research studies published in the literature on the desiccation-induced cracks during the past century, the fundamental mechanism of crack initiation and propagation of soils induced by drying and shrinkage is still elusive. For this reason, the focus of this thesis is directed towards understanding the tensile strength of unsaturated soils which is associated with soil crack initiation criterion (i.e. maximum tensile stress criterion). Tensile strength is the key property of soils for interpreting the initiation of soil cracking from a macroscopic point of view. A semi-empirical model is proposed for predicting the tensile strength of unsaturated cohesionless soils taking into account the effect of both the negative pore-water pressure in saturated pores and the air-water interfacial surface tension in unsaturated pores. The proposed model is calibrated and validated by providing comparisons between the model predictions and the experimental measurements on 10 cohesionless soils (i.e. five sandy soils and five silty soils) published in the literature. The proposed model is simple and requires only the information of Soil-Water Characteristic Curve (SWCC) and Grain Size Distribution curve (GSD), which can be obtained from conventional laboratory tests. To investigate the influence of microstructure, a practical and reliable estimation approach for predicting the evolution of the microstructural void ratio of compacted clayey soils subjected to wetting and drying paths is proposed. The microstructural evolution of 13 examined soils were investigated quantitatively using the mercury intrusion porosimetry (MIP) results. The investigated soils include four high-plasticity clays, eight low-plasticity clays and a glacial till which is a relatively coarse-grained soil with some fines. Based on this study, a novel criterion has been developed for identifying different pore populations of compacted clayey soils. The “as-compacted state line” (ACSL) was proposed to estimate the initial microstructural void ratio based on the compaction water ratio. A constitutive stress is derived to interpret and predict the volumetric deformation of compacted clay aggregates. The linear elastic constitutive model is used for predicting the microstructural void ratio of the examined compacted soils following monotonic wetting and drying paths. The developed approach (i.e. the ACSL and the linear elastic constitutive model) is validated by providing comparisons between the predicted and interpreted microstructural void ratios for all the examined soils. In addition to the matric suction and microstructure, the confining pressure also influences the tensile strength of unsaturated compacted clayey soils. The tensile strength tests on a compacted clayey soil by both the direct method (i.e. triaxial tensile test) and the indirect method (i.e. Brazilian split test) were performed. It is found that the tensile strength increases as the compaction water content decreases for the range investigated in this study, which could be explained by the variation of the inter-aggregated capillary bonding force and the change in microstructure. The increase in the confining pressure has been found to induce the change in failure mode (i.e. from pure tensile failure mode to combined tensile-shear failure mode). In spite of limitations associated with the Brazilian split test, tensile strength is widely determined using this test due to the simple procedure of specimen preparation and wide availability of test equipment in conventional laboratories. However, the Brazilian tensile strength is found to overestimate the tensile strength of compacted specimens with water content greater than the plastic limit. This is due to the considerable plastic deformation associated with the ductile failure instead of brittle failure. In summary, this thesis is devoted to providing insight into the fundamental mechanisms associated with the desiccation-induced crack initiation by quantitatively investigating the various factors that influence the tensile strength of unsaturated soils, which include the matric suction, the microstructure, and the confining pressure from theoretical studies and laboratory investigations.

The tradition of using naturally occurring plant fibers is still alive in Africa. In the Uíge province of northern Angola, bast fibers from Triumfetta cordifolia serve as the basis for everyday objects, such as baskets, mats, fishing nets, and traditional clothing. The fibers exhibit a Young’s modulus of 53.4 GPa and average tensile strength of 916.3 MPa, which are comparable to those of commercial kenaf fibers. These values indicate a high potential for use as a reinforcement in biocomposites. Based on this promising mechanical and physical profile of individual fibers, different biocomposites were produced with polylactide (PLA) as a matrix. The obtained composites were analyzed mechanically, physically, and visually. Unidirectionally arranged PLA/33% T. cordifolia composites with continuous fibers showed the highest Young’s modulus (10.79 GPa ± 1.52 GPa) and tensile strength (79.37 MPa ± 14.01 MPa). These composites were comparable to those of PLA/30% hemp composites (10.9 GPa and 82.9 MPa, respectively) and therefore have economic potential.

L’objectif de cette étude a été de développer des composites à matrice géopolymère synthétisée en voie acide ayant des propriétés mécaniques adaptées aux applications aéronautiques et se conservant entre 300 et 1000 °C. Ces matrices sont synthétisées à partir de métakaolin et d’acide orthophosphorique dilué. Afin d’identifier le domaine de stabilité de ces matrices, leurs évolutions structurelles lors de la consolidation et en température ont été analysées par spectroscopie InfraRouge à Transformée de Fourrier et à Résonance Magnétique Nucléaire ainsi que par Diffraction des Rayons X et ont été corrélées aux analyses dilatométriques. La formulation de la matrice ([P], charges d’Al2O3) a ensuite été adaptée afin d’obtenir un composite à fibres de basalte aux propriétés mécaniques optimales. Compte tenu des faibles propriétés obtenues, d’autres types de fibres oxydes ont été testées et les paramètres procédés ont été adaptés. Enfin, un fois l’ensemble fibres-matrice-procédé optimal identifié, les propriétés mécaniques du composite ont été caractérisées à plus haute température. La microstructure des composites a été déterminée par microscopie électronique à balayage et leurs propriétés mécaniques par des essais de traction et de cisaillement interlaminaire
The aim of this study was to develop composites with an acid-based geopolymer matrix with mechanical properties suitable for aeronautical applications between 300 and 1000 ° C. These matrices are synthesized from metakaolin and dilute orthophosphoric acid. In order to identify the domain of stability of these matrices, their structural changes during consolidation and in temperature were analyzed by Fourier Transform and Nuclear Magnetic Resonance infrared spectroscopy as well as by X-ray diffraction, and were correlated with thermal analyzes. The objective was then to adapt the matrix formulation (consolidation temperature, [P], Al2O3 filler) to obtain a basalt fiber composite with optimal mechanical properties. Due to their poor properties, other types of oxide fibers were tested and the process parameters were adapted. Once the optimum fiber-matrix-process combination was identified, the mechanical properties of the composite were characterized at higher temperatures. The microstructure of the composites was determined by scanning electron microscopy and their mechanical properties by tensile and interlaminar shear tests

La présente thèse s’intéresse à l'alliage à mémoire de forme NiTi, en se concentrant sur l'influence du procédé de nanostructuration superficielle SMAT sur son comportement thermomécanique. À travers quatre chapitres distincts, elle rappelle les principales caractéristiques des alliages à mémoire de forme (AMF), mettant en avant les propriétés exceptionnelles de l'alliage NiTi, et explorant le traitement de nanocristallisation superficielle (SMAT). La caractérisation microstructurale est ensuite approfondie, notamment en étudiant les effets du traitement thermique de recuit et du SMAT sur la transition de phase. Le troisième chapitre se concentre sur les méthodes d'analyse thermomécanique adaptées au NiTi, en examinant les essais de traction et de nanoindentation. Enfin, le quatrième chapitre analyse la caractérisation thermomécanique de l'alliage avant et après le traitement SMAT, mettant en évidence les implications de ces transformations sur son comportement global.La thèse contribue à la compréhension des effets du procédé SMAT sur l'alliage NiTi, révélant des liens entre la microstructure, les phases présentes et les propriétés mécaniques. Les résultats ouvrent des perspectives prometteuses pour la meilleure maîtrise des propriétés de l'alliage NiTi.Les résultats obtenus pour différents traitements SMAT montrent que ce procédé modifie la réponse mécanique du matériau. Elle a aussi une influence sur son état initial, comme l’illustrent les différences dans les courbes de DSC. Les mesures cinématiques (champs de vitesses de déformation) et calorimétriques (champ de source de chaleur) indiquent aussi l’apparition de différences notables dans les réponses en fonction des paramètres de traitement SMAT. L'exploration du comportement lors de cycles de charge/décharge montre une réponse qui se stabiliser après quelques cycles. Les effets de couplage semblent être prépondérants par rapport aux effets dissipatifs. Ces observations devraient être étendues à des chargements en fatigue afin de mieux mettre en évidence les éventuels effets dissipatifs. De même, l’utilisation de modèles d’interprétation plus élaborés permettrait de mieux tenir compte des effets de structure et d’enrichir la compréhension de la relation entre le procédé et les évolutions des propriétés
This thesis focuses on the shape memory alloy NiTi, with a specific emphasis on the influence of the surface nanostructuring process SMAT on its thermomechanical behavior. Through four distinct chapters, it revisits the main characteristics of shape memory alloys (SMAs), highlighting the exceptional properties of the NiTi alloy and exploring the surface nanocrystallization treatment (SMAT). Microstructural characterization is then deeply investigated, particularly by studying the effects of annealing heat treatment and SMAT on phase transition. The third chapter focuses on thermomechanical analysis methods suitable for NiTi, examining tensile tests and nanoindentation. Finally, the fourth chapter analyzes the thermomechanical characterization of the alloy before and after SMAT treatment, highlighting the implications of these transformations on its overall behavior.This thesis contributes to understanding the effects of the SMAT process on the NiTi alloy, revealing links between microstructure, present phases, and mechanical properties. The results offer promising perspectives for better control of the properties of the NiTi alloy.The results obtained for different SMAT treatments show that this process modifies the mechanical response of the material. It also has an influence on its initial state, as illustrated by differences in DSC curves. Kinematic (strain rate fields) and calorimetric (heat source field) measurements also indicate notable differences in responses depending on SMAT processing parameters. Exploration of behavior during load/unload cycles shows a response that stabilizes after a few cycles. Coupling effects seem to be predominant compared to dissipative effects. These observations should be extended to fatigue loading to better highlight any dissipative effects. Similarly, the use of more elaborate interpretation models would allow better consideration of structural effects and enrich the understanding of the relationship between the process and property evolutions

Hundreds of thousands of vascular bypass grafts are implanted in the United States every year, but there has yet to be an ideal graft material to substitute for one’s own autologous vessel. Many synthetic materials have been shown to be successful vessel replacements; however, none have been proven to exhibit the same mechanical properties as native vessels, one of the most important criteria in selecting a vascular graft material. Part of this issue is due to the fact that, currently, there is no “gold standard” for testing the longitudinal and transverse tensile properties of small diameter tubular materials. While there are ASTM and ISO standards that suggest ways to test tubes in their original form, many researchers have published tensile strength data based on cutting the tube and testing it as a flat sample. Thus, it was the aim of this thesis to understand, establish, and implement accurate tensile testing methods of small diameter polymers in their original, tubular state on Cal Poly’s campus. Two test fixtures were created based on specified design criteria in order to test materials in their tubular form in both the longitudinal and transverse directions. Both fixtures were successful in testing PLGA and ePTFE samples, and statistical data was gathered for the transverse test fixture. The new transverse test fixture was tested against the current method of testing, and a significant (α = 0.05) difference between methods was established for ultimate tensile strength. This analysis, however, cannot determine which test method is more accurate, thus more extensive testing is required to verify the design of both fixtures. By developing a method for testing small diameter polymers in tubular form on Cal Poly’s campus, it allows for more testing of various small diameter tubes and more comparative data to validate each design. It also demonstrates a need for a more detailed and widespread standardization of testing for small diameter tubes, especially in vascular substitute applications where the ideal vessel replacement has yet to be found.

This work aims at providing a numerical tool for the efficient design of the multidirectional carbon fiber reinforced composite material by means of finite element simulations. Abaqus/ CAE v 6.9-1 software has been used to establish a 3D model for simulation of the tensile test on the composite specimen. The aim of this analysis of multidirectional carbon fiber reinforced composite is to predict the strain and stress distribution in different plies through thickness. Tensile test experiment was carried out and the result was analyzed by ARAMIS to calculate the young’s modulus, stress, loads and strain of the composite specimen. The numerical model was compared against the result obtained from tensile test experiment to arrive at meaningful results for validation. This is done in order to understand the mechanical strength and strain at failure of the composite material. In this work three types of CFRP composite specimens are used, all have same 15 no. of ply but stacked in different orientation. It is found out that mechanical strength, failure load and strain differ slightly depending on this different ply orientation. A series of different modeling technique has also been done to verify the best modeling technique. The micromechanics of composite material is complex and the experimental predictions are time consuming and expensive. Though using FEM frequently solves the problem.

This thesis is concerned with several aspects of fracture of both brackish (low salinity) sea ice and freshwater ice. The tests and analyses are confined to tensile, or in fracture mechanics language, Mode I, fracture. A large part of this thesis is dedicated to demonstrate that Linear Elastic Fracture Mechanics (LEFM) can be applicable on ice by laboratory and in-situ tests of defined specimens. All interpretations are made using the dicipline of LEFM.First, the development of a field test equipment called FIFT ( a Field Instrument for Fracture toughness Tests on ice) is described. The FIFT is used in both field and laboratory fracture toughness tests on brackish sea ice from the Gulf of Bothnia to describe porosity effects on the apparent fracture toughness, KQ, and estimate crack velocities. An appropriate speciment size, in terms of notch sensitivity, is then provided valid for grain sizes ranging from 1.6 to nearly 100 mm.An augmented use of the FIFT is then described where fracture toughness tests are performed on S1 type freshwater ice to investigate if similarities exist in the local KI fields for three different fracture geometries. The results indicate that, under comparable conditions, KQ is similar for all of the geometries. However, the type of specimen, has a marked influence on the character of the fracture surface.Then, the influence of structural anisotropy on the fracture toughness of S1 ice is investigated by fabricating and testing three different fracture geometries from a single ice core. This approach is suitable for both field and, as in this work, laboratory studies. There is a wide scatter in the KQ values. Possible explanations to the results are discussed in terms of the microstructural influences and specimen size effects.Finally, crack growth resistance measurements on large grained S1 ice is conducted. A new fracture geometry is used which is found to be extremely favorable of promoting stable, stick-slip, crack growth over a large portion of the uncracked ligament. Now a complete characterization of the fracture resistance curve is therefore possible, A negative fracture resistance KR-curve is evaluated for the S1 ice at -16°C.
Godkänd; 1993; 20070426 (ysko)

Paperboard combined with polymer and aluminium films are widely used in food packages. Paperboard is used for the bulk of the package material, and provides the stiffness. Paperboard is a highly anisotropic material, which is affected by how the fibers are orientated. Most fibers are aligned in the machine direction (MD), which is the stiffest direction, perpendicular is the cross-machine direction (CD) where fewer fibers are aligned, and the thickness direction (ZD) which is considerably weaker than in the MD and CD directions. Continuum models are used to describe the material properties to aid the design of package manufacturing processes. In continuum models there are no inherent length scale effects, and the material behaviour is the same regardless of the geometry. For paperboard there have been experimentally observed effects of the gauge length and width of tensile tests. To calibrate and develop these models it is important to observe which effect is a material property, if there is an inherent length scale, and which properties are from the boundary conditions of the experimental setup. Creasing is a process where the length scale is considerably smaller than at the standard tensile test, where the material deforms plastically to create creasing lines to easier fold the paperboard. The failure properties from standard tensile tests are not a good predictor of failure in creasing, where the length scale is considerably smaller. To investigate if there is an effect of the length scale, as the length gets smaller, tensile tests have been performed at different gauge lengths. The tensile tests were performed with a width of 15mm and the gauge length was varied in the range 3-100mm in MD and CD. The results from the tensile tests were, the failure strain and failure stress increased as the gauge length of the tests specimens decreased, both in MD and in CD. Initial stiffness decreased as the gauge length decrease (more notable in MD), and there was an increase in hardening at large strains with decreasing gauge length (more notable in CD). An analytical calculation of the reduction in measured stiffness as the gauge length get smaller was performed, where the decrease in stiffness deemed to be strongly related to the out-of-plane shear modulus. By fitting the analytical solution the experimental data the shear modulus was approximated to 60MPa. The shear modulus has been measured for the same paperboard to 70±23MPa. Simulations of the tensile tests at 5mm did fit the experimental data when the material model was calibrated from the tensile test at 100mm, except the increase in hardening at large strains in CD. It was noted that it was important to use the shear modulus that was inversely calculated by the analytical calculations to get the right initial slope of the simulations of the 5mm tensile tests. Creasing simulations were performed of a test setup of the creasing procedure. The male die was lowered 0.3mm to perform the creasing, which in the tests setup do not result in failure in the material. From the simulations the stress at the bottom of the paperboard during creasing exceeded the failure stress from the tensile test performed at 100mm. The stress during creasing was biaxial, it has stresses both in MD and CD, with is different compared to the uniaxial tensile tests at 100mm. The stress from the creasing simulation in CD was at a maximum of 40MPa where the 3mm tensile tests in CD resulted in a failure stress at 39MPa. The maximum stress in the MD creasing simulation was 96MPa, where the 3mm tensile test resulted in a failure stress at 69MPa. The properties from a long span tensile test are not good predictors of failure in creasing, where both stress state and length scale are very different. The failure stress at 3mm tensile tests in CD is close to the maximum stress from creasing simulations, and may be a good indication of failure. The 3mm tensile test in MD resulted in a considerably lower failure stress than the maximum stress in the creasing simulations, which indicates that the 3mm long tensile test is not a good predictor of failure in MD for creasing, where the length scale is even smaller.

Afin de traiter les patients atteint de diabète de type 1, un pancréas bioartificiel permettant d’encapsuler des cellules produisant de l’insuline a été développé : il est constitué de membranes poreuses qui les isolent des anticorps du patient, tout en permettant le passage du glucose et de l’insuline. Avant sa mise sur le marché, il est nécessaire de vérifier que son comportement mécanique lui permet d’être implanté chez l’homme sans risque pour le patient. La résistance des membranes sous chargement mécanique est donc étudiée en particulier. Leur structure est d’abord mise en évidence par microscopie électronique à balayage et nanotomographie à rayons X. Des essais de traction sont ensuite effectués à l’échelle macroscopique et à l’échelle microscopique, l’utilisation de techniques de mesure de champs par corrélation d’images permettant de caractériser les déformations des membranes à chaque échelle. En parallèle, une modélisation numérique par éléments finis est développée en se basant sur les caractéristiques microstructurales et mécaniques des membranes. Une méthodologie de comparaison entre le comportement prédit par le modèle et le comportement expérimental des membranes est alors proposée et utilisée. Les résultats de cette étude sont finalement considérés pour juger de la possibilité d’utiliser ce dispositif en phase clinique
In order to treat type 1 diabetics, a bioartificial pancreas has been developed. It consists in the encapsulation of insulin producing cells: it is made of porous membranes which isolate cells from patient antibodies, allowing the glucose and the insulin to pass through. Before its commercialization, it is necessary to verify that its mechanical behavior allows it to be implanted in a human body without any risk for the patient. The mechanical strength of the membranes under loading is therefore studied. Their structure is first obtained using scanning electron microscopy and X-ray nanotomography. Tensile tests are then done at both macroscopic and microscopic scales, digital image correlation techniques being used to characterize the membranes at each scale. At the same time, a numerical model using finite element method is built based on the microstructural and mechanical characteristics of the membranes experimentally identified. A methodology to compare the experimental and numerical results behavior of the membranes is proposed and used. The results of the study are finally considered to assess the possibility to use the device in clinic phase

Uvođenje nanočestica u stomatološke kompozitne materijale predstavlja pokušaj da se odgovori univerzalnim zahtevima za kvalitetom direktnog zubnog ispuna, i da se stvori materijal koji kombinuje visoku mehaničku otpornost sa dobrim estetskim karakteristikama i zadovoljavajućim kvalitetom poliranja. Cilj sprovedene studije je bio da se ispita uticaj nanočestica, i soft-start metode svetlosne indukcije polimerizacije na mehanička i površinska svojstva savremenih stomatoloških nanokompozita, dostupnih na tržištu. Ispitana su četiri stomatološka nanostrukturisana kompozitna materijala na bazi smola i jedan univerzalni mikrohibridni kompozit, kao referentni materijal (Filtek Z250, 3M ESPE). Korišćena su po dva reprezentativna materijala iz dve podgrupe nanokompozita: nanopunjenih (Filtek Ultimate Body, 3M ESPE i Filtek Ultimate Translucent, 3M ESPE) i nanohibridnih kompozita (Filtek Z550, 3M ESPE i Tetric EvoCeram, Ivoclar Vivadent - TEC). Uzorci su polimerizovani nakon svetlosne aktivacije polimerizacije, uz korišćenje dva svetlosna režima: konvencionalnog i soft start režima. Pritisna i zatezna čvrstoća (dobijena poprečnim sabijanjem valjka, engl. diametral tensile strength) testirane su na Univerzalnoj mašini, kidalici. Tvrdoća uzoraka merena je testom za određivanje tvrdoće po Vickersu. Površinska tekstura i parametri hrapavosti određeni su skeniranjem površine mikroskopom atomskih sila. Uopšteno, TEC je pokazao najniže vrednosti pritisne i zatezne čvrstoće, i tvrdoće, i statistićki je značajno bio slabiji od drugih testiranih materijala kroz sve mehaničke testove. Suprotno, TEC je imao najniže vrednosti parametara hrapavosti među testiranim materijalima. Spoj prepolimerizovanog punioca i polimerne baze u ovom materijalu pokazao se kao njegova slaba tačka. Navedeni materijal je iz tog razloga pokazao značajno slabiju otpornost od ostalih na razvijene napone izazvane dejstvom mehaničkih sila. Čestice nanodimenzija u sastavu stomatoloških polimernih kompozita, samostalno, nisu imale značajan uticaj na poboljšanje mehaničkih i površinskih svojstava testiranih kompozita. Zaključeno je i da se procentualna zastupljenost neorganskih čestica u polimernoj bazi ne može smatrati apsolutnim kriterijumom kvaliteta kompozita, u pogledu njihovih mehaničkih svojstava. Samo srodni materijali, izrađeni istim tehnološkim postupkom, koji imaju veoma sličan ili isti hemijski sastav, pokazali su se kao mehanički superiorniji ukoliko su sadržali veći procenat neorganske komponente u svom sastavu. Nano prefiks u nazivu klase materijala ne garantuje sigurnu prednost stomatoloških nanokompozita nad univerzalnim mikrohibridnim kompozitima.
The introduction of nanoparticles in dental composite materials was an attempt to respond to the universal quality requirements for a direct dental restoration, and to create a material that meets the needs of high mechanical resistance, good aesthetic characteristics and surface properties of tooth restoratives. The aim of this study was to investigate the effect of nanoparticles in materials composition, and the soft start photoactivation method on the mechanical and surface properties of contemporary dental nanocomposites, available in the market. Four dental resin based nanostructured composites were tested along with a universal microhybrid one, as reference material (Filtek Z250, 3M ESPE). Two representative materials from the two classification subgroups were tested, nanofilled (Filtek Ultimate Body, 3M ESPE and Filtek Ultimate Translucent, 3M ESPE) and nanohybrid composites (Filtek Z550, 3M ESPE and Tetric EvoCeram, Ivoclar Vivadent, TEC). Polymerization of the samples was light activated using two light modes: conventional and soft start. Compressive and diametral tensile strength were tested on the Universal testing machine. The Vickers hardness was also determined. Surface texture and roughness parameters were examined by atomic force microscopy. Generally, TEC showed the lowest values of compression, tensile strength and hardness, and was statistically different from the other tested materials throughout all mechanical tests. In contrast, TEC had the lowest values of roughness parameters among the tested materials. In this material, contact zone of prepolimeryzed filler and polymer matrix appeared to be a weak point. For this reason, this material showed significantly lower resistance than the others on mechanically developed stresses. Nanosized particles within the dental polymer composites, individually, did not have a significant influence on improving the mechanical and surface properties of tested composites. It is concluded that the inorganic volume fraction in composites cannot be considered as an absolute criterion of their quality, regarding their mechanical properties. Only similar materials, made using the same technological process, which have very similar or the same chemical composition, and similar technological method of synthesis and optimization of organic and inorganic components, showed improved mechanical strength, if they contained a higher percentage of inorganic components in their composition. Nano prefix in the name of material’s class does not guarantee the pure advantage of dental nanocomposites in comparison with the universal microhybrid composites.

COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
O objetivo foi estudar a aderência entre o compósito de fibra de carbono (CFC) e o substrato de concreto, em corpos-de-prova compostos de cubos de concreto, por meio do ensaio de tração-compressão. Foram ensaiados 18 corposde- prova compostos de dois cubos de concreto (móvel e fixo) ligados por tiras de CFC coladas às suas laterais opostas onde a região à ser estudada foi devidamente instrumentada. Os parâmetros estudados foram a resistência do concreto, o tipo de carregamento (monotônico crescente e carregamento em ciclos de carga e descarga) e as diferentes superfícies do concreto (superfície lisa e superfície rugosa). Os resultados dos ensaios mostraram que para as diferentes resistências à compressão do concreto no intervalo estudado não se obteve uma formulação que indicasse a influencia da resistência à compressão sob a resistência última de aderência, para a qual foi obtido um valor característico igual a 1,44 MPa. Foram medidas as deformações específicas do CFC assim como do concreto, com as quais foram calculadas as tensões de aderência e as deformações específicas. Com os resultados experimentais foram obtidos gráficos e curvas de ajuste para energia de fratura vs. resistência de aderência. Com o critério de Coulomb-Mohr generalizado pode-se estimar como valor inicial a resistência de aderência da ordem de 30% da tensão tangencial máxima resistida pelo substrato de concreto.
The purpose of this work was study the bond between the composite of fiber carbon (CFC) and the concrete substratum. A total of 18 tension-compression tests on specimens with two concrete cubes (fixed and movable) linked by fiber carbon on opposites sides were performed. The area to be studied was properly monitored. The variables of these tests were the concrete strength, the loading type (monotonic loading and loading/unloading cycles), and different concrete surfaces (smooth face and rough face). The test results showed that in the interval analyzed, could not be obtain a formulation that indicates the influence of ultimate bond stress on concrete strength. A characteristic value of 1,44 MPa was obtained for the ultimate bond stress. The specific deformations of CFC and concrete were measured, allowing to calculate the bond stress and the corresponding mean strain. The experimental results provided graphs and adjustment curves for energy of fracture vs. bond stress. With the Coulomb- Mohr criteria it can be considered as initial value for bond stress 30% of the concrete mean shear strain.