Variación de las características mecánicas de armaduras de alta ductilidad B500SD en función de su grado de corrosión / Mechanical properties variation of B500SD high ductility reinforcement regarding its corrosion degree

Los efectos de la corrosión sobre las armaduras se manifiestan por la pérdida de sección y la variación de las propiedades mecánicas relacionadas con la ductilidad. En este trabajo se han ensayado a tracción 96 barras de acero B500SD que previamente se han sometido a niveles variables de corrosión. Los resultados muestran que los alargamientos de las barras disminuyen y el cociente entre la tensión máxima y el límite elástico aumenta conforme el nivel de corrosión avanza. A partir del estudio del efecto de entalla y de la distinta constitución metalográfica del acero a nivel de sección debido a su procedimiento de fabricación se pueden explicar los fenómenos anteriores.

Caraterização das propriedades macânicas e de fratura de um adesivo estrutural de alta ductilidade

As juntas adesivas são uma alternativa viável para substituir ligações comuns como as mecânicas ou soldadas, devido a diversas vantagens como a possibilidade de união de materiais de natureza diferente, maior leveza, menores custos inerentes ao fabrico e ainda prevenção da corrosão galvânica que pode ocorrer nas ligações entre dois materiais metálicos diferentes. A resistência de uma junta depende, para um determinado tipo de solicitação imposta, da distribuição de tensões no interior da junta. Por outro lado, a geometria das juntas, as propriedades mecânicas dos adesivos e os componentes a ligar vão influenciar a distribuição de tensões. O carregamento nas camadas adesivas de uma junta poderá induzir tensões de tração, compressão, corte, arrancamento ou clivagem, ou ainda uma combinação de duas ou mais destas componentes. O objetivo da presente dissertação é a caraterização completa de um adesivo estrutural de alta ductilidade recentemente lançado no mercado (SikaPower® -4720), para facilitar o projeto e otimização de juntas adesivas ligadas com o mesmo. São quatro os ensaios a realizar: ensaios à tração de provetes maciços (também denominados de bulk), ensaios ao corte com a geometria Thick Adherend Shear Test, ensaios Double-Cantilever Beam e ainda ensaios End-Notched Flexure. Com a realização dos ensaios referidos, são determinadas as propriedades essenciais à caraterização mecânica e de fratura do adesivo. Os resultados obtidos para cada ensaio resultaram em propriedades medidas com elevada repetibilidade, da mesma maneira que se revelaram de acordo com os dados disponibilizados pelo fabricante, sempre que estes estavam disponíveis.

Assessment of overlay masonry strengthening system under in-plane monotonic and cyclic loading using the diagonal tensile test

The development of novel strengthening techniques to address the seismic vulnerability of masonry elements is gradually leading to simpler, faster and more effective strengthening strategies. In particular, the use of fabric reinforced cementitious matrix systems is considered of great potential, given the increase of ductility achieved with simple and economic strengthening procedures. To assess the effectiveness of these strengthening systems, and considering that the seismic action is involved, one important component of the structural behaviour is the in-plane cyclic response. In this work is discussed the applicability of the diagonal tensile test for the assessment of the cyclic response of strengthened masonry. The results obtained allowed to assess the contribution of the strengthening system to the increase of the load carrying capacity of masonry elements, as well as to evaluate the damage evolution and the stiffness degradation mechanisms developing under cyclic loading.

Flexural strengthening of RC beams using hybrid composite plate (HCP): experimental and analytical study

Hybrid Composite Plate (HCP) is a reliable recently proposed retrofitting solution for concrete structures, which is composed of a strain hardening cementitious composite (SHCC) plate reinforced with Carbon Fibre Reinforced Polymer (CFRP). This system benefits from the synergetic advantages of these two composites, namely the high ductility of SHCC and the high tensile strength of CFRPs. In the materialstructural of HCP, the ultra-ductile SHCC plate acts as a suitable medium for stress transfer between CFRP laminates (bonded into the pre-sawn grooves executed on the SHCC plate) and the concrete substrate by means of a connection system made by either chemical anchors, adhesive, or a combination thereof. In comparison with traditional applications of FRP systems, HCP is a retrofitting solution that (i) is less susceptible to the detrimental effect of the lack of strength and soundness of the concrete cover in the strengthening effectiveness; (ii) assures higher durability for the strengthened elements and higher protection to the FRP component in terms of high temperatures and vandalism; and (iii) delays, or even, prevents detachment of concrete substrate. This paper describes the experimental program carried out, and presents and discusses the relevant results obtained on the assessment of the performance of HCP strengthened reinforced concrete (RC) beams subjected to flexural loading. Moreover, an analytical approach to estimate the ultimate flexural capacity of these beams is presented, which was complemented with a numerical strategy for predicting their load-deflection behaviour. By attaching HCP to the beams’ soffit, a significant increase in the flexural capacity at service, at yield initiation of the tension steel bars and at failure of the beams can be achieved, while satisfactory deflection ductility is assured and a high tensile capacity of the CFRP laminates is mobilized. Both analytical and numerical approaches have predicted with satisfactory agreement, the load-deflection response of the reference beam and the strengthened ones tested experimentally.

Assessment of the properties to characterize the interface between clay brick substrate and strengthening mortar

The behaviour of masonry elements under in-plane and out-of-plane loads can be improved through the application of strengthening systems based on reinforcing overlays. After strengthening, the transition region between the original substrate and the strengthening layer is especially stressed, and premature failure of the strengthened masonry is reached if insufficient interfacial capacity is assured. Therefore, the assessment of the mechanical behaviour of the interface is critical to the development of the masonry strengthening system based on the application of strengthening overlays. In this research a method for the characterization of the interface behaviour between two different materials, a polypropylene fibre reinforced mortar (PFRM) and a ceramic brick used for masonry construction is presented. Direct shear tests were carried out in couplet specimens. Due to the orthotropic nature of the bricks surface, the shear load was applied along three different directions in order to perform an overall estimation of the interface behaviour. The peak and residual shear stresses, as well as the failure modes, were obtained at different levels of the normal stress. Based on these experimental results constitutive laws were assessed for the simulation of the interface mechanical behaviour based on the Mohr and Mohr-Coulomb failure criteria.

Development of hybrid composite plate (HCP) for strengthening and repair of RC structures

Tese de Doutoramento em Engenharia Civil

Estudo da ligação entre componentes estruturais de GFRP (glass fiber reinforced polymer) e componentes estruturais em betão

Dissertação de mestrado integrado em Engenharia Civil

Adição de vermiculita expandida mícron em pastas de baixa densidade para cimentação de poços de petróleo

The northeastern region of Brazil has a large number of wells producing oil using a method of secondary recovery steam injection, since the oil produced in this region is essentially viscous. This recovery method puts the cement / coating on thermal cycling, due to the difference in coefficient of thermal expansion between cement and metal coating causes the appearance of cracks at this interface, allowing the passage of the annular fluid, which is associated with serious risk socioeconomic and environmental. In view of these cracks, a correction operation is required, resulting in more costs and temporary halt of production of the well. Alternatively, the oil industry has developed technology for adding new materials in cement pastes, oil well, providing high ductility and low density in order to withstand the thermo-mechanical loads generated by the injection of water vapor. In this context, vermiculite, a clay mineral found in abundance in Brazil has been applied in its expanded form in the construction industry for the manufacture of lightweight concrete with excellent insulation and noise due to its high melting point and the presence of air in their layers lamellar. Therefore, the vermiculite is used for the purpose of providing low-density cement paste and withstand high temperatures caused by steam injection. Thus, the present study compared the default folder containing cement and water with the folders with 6%, 8% and 10% vermiculite micron conducting tests of free water, rheology and compressive strength where it obtained the concentration of 8 % with the best results. Subsequently, the selected concentration, was compared with the results recommended by the API standard tests of filtered and stability. And finally, analyzed the results from tests of specific gravity and time of thickening. Before the study we were able to make a folder with a low density that can be used in cementing oil well in order to withstand the thermo-mechanical loads generated by steam injection

Corrosion resistance enhancement of SAE 1020 steel after Chromium implantation by nitrogen ion recoil

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Desenvolvimento e caracterização de compósitos poliméricos reforçados com fibras lignocelulósicas: HIPS / fibra de casca do coco verde e bagaço de cana de açucar

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Caracterização mecânica e microestrutural de juntas soldadas a laser em aços maraging com posterior tratamento térmico e termoquímico de superfície a plasma

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Simulación de la rotura de barras de acero perlítico sometidas a tracción mediante un modelo de fisura cohesiva. Validación experimental

Las probetas cilíndricas fabricadas con materiales metálicos de elevada ductilidad, como el aluminio o el cobre, sometidas a tracción suelen presentar una rotura comúnmente denominada rotura en copa y cono, debido a su geometría. Este tipo de rotura se reproduce numéricamente con éxito mediante el modelo de Gurson-Tvergaard- Needleman, cuya formulación matemática se basa en el fenómeno físico de nucleación, crecimiento y coalescencia de microhuecos. A diferencia de dichos materiales, las barras de acero perlítico, material con una ductilidad apreciable, presentan un frente de rotura plano que no puede simularse correctamente con los modelos antes mencionados, apareciendo una región interior de daño que, en principio, también puede atribuirse a un fenómeno de nucleación y crecimiento de microhuecos, mientras que en el exterior aparece una zona cuya micrografía permite asociar su rotura a un mecanismo de clivaje. En trabajos anteriores los autores han presentado un elemento de intercara cohesivo dependiente de la triaxialidad de tensiones que, incorporado a un código de elementos finitos, permite reproducir de forma razonable el daño que se desarrolla en la región interior mencionada. En este trabajo se presentan los resultados de una campaña experimental que permite validar el modelo desarrollado. Para ello, se ensayan probetas de diferentes diámetros y se comparan los resultados con los obtenidos numéricamente, empleando tres bases extensométricas diferentes en cada uno de los diámetros. Los resultados numéricos se ajustan razonablemente bien a los obtenidos experimentalmente.The cylindrical specimens made of high-ductility metallic materials, such as aluminium and copper, usually fail showing a fracture surface commonly known as cup-cone fracture because of its shape. This type of fracture is successfully reproduced using the Gurson-Tvergaard-Needleman model, which is based on the physical process of nucleation, growth and coalescence of microvoids. Unlike these materials, pearlitic steel bars, which are considerably ductile, show a flat fracture surface that cannot be correctly reproduced with the aforementioned models. In this flat fracture surface, a dark region can be observed in the centre of the specimen, which is the result of a process of nucleation and growth of microvoids, while in the rest of the fracture surface a different region can be identified, which a micrographic study reveals to be the result of a process of cleavage. In previous works, the authors presented a triaxiality-dependent cohesive interface element that, implemented in a finite element code, can reproduce in a reasonably accurate manner the damage that takes place in the dark region mentioned before. The results of an experimental campaign designed to validate the model are presented in this paper. For it, different diameter specimens are tested and these results are compared to those obtained with the numerical models, using three different initial lengths for the strain. Numerical results agree reasonably well with those obtained experimentally.

Simulación de la rotura de barras de acero perlítico sometidas a tracción mediante un modelo de fisura cohesiva. Validación experimental

Las probetas cilíndricas fabricadas con materiales metálicos de elevada ductilidad, como el aluminio o el cobre, sometidas a tracción suelen presentar una rotura comúnmente denominada rotura en copa y cono, debido a su geometría. Este tipo de rotura se reproduce numéricamente con éxito mediante el modelo de Gurson-Tvergaard- Needleman, cuya formulación matemática se basa en el fenómeno físico de nucleación, crecimiento y coalescencia de microhuecos. A diferencia de dichos materiales, las barras de acero perlítico, material con una ductilidad apreciable, presentan un frente de rotura plano que no puede simularse correctamente con los modelos antes mencionados, apareciendo una región interior de daño que, en principio, también puede atribuirse a un fenómeno de nucleación y crecimiento de microhuecos, mientras que en el exterior aparece una zona cuya micrografía permite asociar su rotura a un mecanismo de clivaje. En trabajos anteriores los autores han presentado un elemento de intercara cohesivo dependiente de la triaxialidad de tensiones que, incorporado a un código de elementos finitos, permite reproducir de forma razonable el daño que se desarrolla en la región interior mencionada. En este trabajo se presentan los resultados de una campaña experimental que permite validar el modelo desarrollado. Para ello, se ensayan probetas de diferentes diámetros y se comparan los resultados con los obtenidos numéricamente, empleando tres bases extensométricas diferentes en cada uno de los diámetros. Los resultados numéricos se ajustan razonablemente bien a los obtenidos experimentalmente.The cylindrical specimens made of high-ductility metallic materials, such as aluminium and copper, usually fail showing a fracture surface commonly known as cup-cone fracture because of its shape. This type of fracture is successfully reproduced using the Gurson-Tvergaard-Needleman model, which is based on the physical process of nucleation, growth and coalescence of microvoids. Unlike these materials, pearlitic steel bars, which are considerably ductile, show a flat fracture surface that cannot be correctly reproduced with the aforementioned models. In this flat fracture surface, a dark region can be observed in the centre of the specimen, which is the result of a process of nucleation and growth of microvoids, while in the rest of the fracture surface a different region can be identified, which a micrographic study reveals to be the result of a process of cleavage. In previous works, the authors presented a triaxiality-dependent cohesive interface element that, implemented in a finite element code, can reproduce in a reasonably accurate manner the damage that takes place in the dark region mentioned before. The results of an experimental campaign designed to validate the model are presented in this paper. For it, different diameter specimens are tested and these results are compared to those obtained with the numerical models, using three different initial lengths for the strain. Numerical results agree reasonably well with those obtained experimentally.

Efeito da moagem de alta energia na densificação e microestrutura do compósito AI2O3-Cu

The Cu-Al2O3 composite ceramic combines the phase of alumina, which is extremely hard and durable, yet very brittle, to metallic copper phase high ductility and high fracture toughness. These characteristics make this material a strong candidate for use as a cutting tool. Al2O3-Cu composite powders nanocrystalline and high homogeneity can be produced by high energy milling, as well as dense and better mechanical structures can be obtained by liquid phase sintering. This work investigates the effect of high-energy milling the dispersion phase Al2O3, Cu, and the influence of the content of Cu in the formation of Cu-Al2O3 composite particles. A planetary mill Pulverisatte 7 high energy was used to perform the experiments grinding. Al2O3 powder and Cu in the proportion of 5, 10 and 15% by weight of Cu were placed in a container for grinding with balls of hard metal and ethyl alcohol. A mass ratio of balls to powder of 1:5 was used. All powders were milled to 100 hours, and powder samples were collected after 2, 10, 20, 50 and 70 hours of grinding. Composite powders with compact cylindrical shape of 8 mm diameter were pressed and sintered in uniaxial matrix resistive furnace to 1200, 1300 to 1350 °C for 60 minutes under an atmosphere of argon and hydrogen. The heating rate used was 10°C/min. The powders and structures of the sintered bodies were characterized by XRD, SEM and EDS. Analysis TG, DSC and particle size were also used to characterize the milled powders, as well as dilatometry was used to observe the contraction of the sintered bodies. The density of the green and sintered bodies was measured using the geometric method (mass / volume). Vickers microhardness with a load of 500 g for 10 s were performed on sintered structures. The Cu-Al2O3 composite with 5% copper density reached 61% of theoretical density and a hardness of 129 HV when sintered at 1300 ° C for 1h. In contrast, lower densities (59 and 51% of the theoretical density) and hardness (110 HV and 105) were achieved when the copper content increases to 10 and 15%.

Sensibilidade à mudança de trajetória de deformação no aço TWIP980

Resultante dos avanços tecnológicos, conseguiu-se obter um aço que elimina o paradigma de se aliar alta ductilidade e resistência mecânica. Assim foi desenvolvido durante a última década o aço TWIP, deformação induzida por maclação, tendo como principal mecanismo de deformação a maclação. Este presente trabalho teve como principal objetivo caraterizar o aço TWIP980 em três temáticas diferentes: química, mecânica e microestrutura. Na primeira temática, a química, esta teve como objetivo encontrar a designação do aço TWIP em estudo. Sendo apenas conhecida a direção de laminação, RD, e a empresa que forneceu as chapas, a POSCO, o objetivo era obter a sua designação. Através da comparação das curvas de tração encontradas para o material em estudo, e conjuntamente, com as diversas curvas de tração de vários aços TWIP da empresa POSCO, realizou-se a comparação. Visto ter-se ficado reduzido a dois possíveis aços TWIP, foi através de uma análise à composição química, EDS - Espectroscopia da energia dispersa por raios-X, que se concluiu que o aço em estudo era o TWIP980. Na caraterização mecânica, e através de ensaios de tração, foram estudadas propriedades como: o módulo de elasticidade, tensão limite elástico, ductilidade, anisotropia, coeficiente de encruamento e Poisson. Estas propriedades foram estudas para três mudanças na trajetória de deformação e quatro pré-deformações em estudo. Assim estudou-se a alteração de trajetória para os ângulos a 0º, 45º e 90º em relação a RD, para as deformações de engenharia de 0%, 10%, 20% e 30%. Por último, na análise à microestrutura, esta teve como objetivo obter valores para o tamanho de grão e de macla bem como as suas orientações cristalográficas. Também a densidade de deslocações e maclação para cada uma das 4 pré-deformações esteve em estudo. Estes parâmetros foram obtidos através de microscopia ótica, eletrónica de varrimento, MEV e eletrónica de transmissão, MET.