Aços de alta resistência e baixa liga (ARBL) são uma alternativa atraente em aplicações estruturais. Devido ao baixo teor de carbono e de elementos de liga (Ni, V e Ti), os aços ARBL apresentam bons níveis de tenacidade e de resistência mecânica, além de boa soldabilidade, permitindo assim, o uso de componentes estruturais mais leves, a economia no consumo de combustível, bem como o desenvolvimento de construções ambientalmente corretas. A boa combinação de propriedades mecânicas permite que os aços ARBL sejam amplamente utilizados na construção naval, na indústria petrolífera e na indústria automotiva. Para estas aplicações, a tecnologia de soldagem é inevitável, a qual produz alterações microestruturais localizadas e redução dos níveis de resistência mecânica, tensões residuais e defeitos indesejáveis, que geram problemas potenciais de segurança e de confiabilidade. Estes defeitos de soldagem acentuam o processo de falha de fadiga, quando componentes mecânicos são submetidos a cargas cíclicas. Neste trabalho, estudou-se a influência do processo de soldagem por arco elétrico com atmosfera de proteção gasosa (GMAW) na microestrutura, propriedades mecânicas e resistência à fadiga do aço ARBL DIN EN 10149 S700MC, aplicando três velocidades de soldagem e dois diferentes metais de adição (AWS ER 70 S – 6 e AWS E 110C-G-M). Para isso, corpos de prova deste aço ARBL e juntas soldadas desses dois metais de adição foram estudadas por meio de análises microestruturais, ensaios de tração uniaxial, microdureza e ensaios de fadiga por tração uniaxial. Os resultados mostraram que a velocidade de soldagem não causou alterações significativas na microestrutura do metal de solda e da zona termicamente afetada, na microdureza e na resistência à tração, quando foi utilizado o mesmo metal de solda. Porém, maiores velocidades de soldagem causaram o aumento do defeito de mordedura. Além disso, verificou-se um aumento da vida em fadiga do componente com a diminuição da velocidade de soldagem. Quando comparadas as amostras soldadas com uma mesma velocidade de soldagem, observou-se um aumento da proporção de ferrita acicular no metal de solda, um aumento da tensão de ruptura e, consequentemente, uma melhora da vida em fadiga do componente, em função do aumento da resistência mecânica do metal de solda. / Submitted by Ana Guimarães Pereira (agpereir@ucs.br) on 2017-05-10T18:40:43Z No. of bitstreams: 1 Dissertacao Rui Gustavo Lippert Schwanke.pdf: 11672515 bytes, checksum: 14a40d04483fb3216e392d56449ded89 (MD5) / Made available in DSpace on 2017-05-10T18:40:43Z (GMT). No. of bitstreams: 1 Dissertacao Rui Gustavo Lippert Schwanke.pdf: 11672515 bytes, checksum: 14a40d04483fb3216e392d56449ded89 (MD5) Previous issue date: 2017-05-10 / Conselho Nacional de Desenvolvimento Científico e Tecnológico. / High strength and low alloy steels (HSLA) are attractive alternative in structural applications. Due to the low carbon and alloying elements (Ni, V and Ti) contents, HSLA steels show good levels of toughness and mechanical strength, besides good weldability, allowing use of lighter structural components, fuel economy, as well as the development of environmentally-friendly constructions and sustainable societies. The good combination of mechanical properties allows HSLA steels to be widely used in shipbuilding oil industry and automotive industry. For these applications, welding technology is inevitable, however it produces localized microstructural changes and reduction in the levels of mechanical strenght, residual stresses and undesirable defects, which generate potential problems of security and reliability. These welding defects accentuate the fatigue failure process when mechanical components are subjected to cyclic loads. In this work, the influence of the gas metal arc welding process (GMAW) on microstructure, mechanical properties and fatigue life of the HSLA DIN EN 10149 S700MC steel was studied, applying three welding speeds and two different addition metals (AWS ER 70 S-6 and AWS E 110C-G-M). For this purpose, samples of this HSLA steel and welded joints of these two addition metals were studied by microstructural analysis, uniaxial tension tests, microhardness tests and uniaxial tension fatigue tests. The results showed that the welding speed did not cause significant changes in the microstructure of the weld metal and of the heat-affected zone, in the microhardness and in the tensile strength, when the same weld metal was used. However, higher welding speeds caused the increase of the undercut defect. Besides that, an increase in fatigue life of the component with the decrease in welding speed was verified. When welded samples produced with the same welding speed were compared, an increase in the ratio of acicular ferrite in the weld metal zone, in the tensile stress and, consequently, an improvement in the fatigue life of the component was observe as a function of the increase in mechanical resistance of the weld metal.

Aços de alta resistência e baixa liga (ARBL) são uma alternativa atraente em aplicações estruturais. Devido ao baixo teor de carbono e de elementos de liga (Ni, V e Ti), os aços ARBL apresentam bons níveis de tenacidade e de resistência mecânica, além de boa soldabilidade, permitindo assim, o uso de componentes estruturais mais leves, a economia no consumo de combustível, bem como o desenvolvimento de construções ambientalmente corretas. A boa combinação de propriedades mecânicas permite que os aços ARBL sejam amplamente utilizados na construção naval, na indústria petrolífera e na indústria automotiva. Para estas aplicações, a tecnologia de soldagem é inevitável, a qual produz alterações microestruturais localizadas e redução dos níveis de resistência mecânica, tensões residuais e defeitos indesejáveis, que geram problemas potenciais de segurança e de confiabilidade. Estes defeitos de soldagem acentuam o processo de falha de fadiga, quando componentes mecânicos são submetidos a cargas cíclicas. Neste trabalho, estudou-se a influência do processo de soldagem por arco elétrico com atmosfera de proteção gasosa (GMAW) na microestrutura, propriedades mecânicas e resistência à fadiga do aço ARBL DIN EN 10149 S700MC, aplicando três velocidades de soldagem e dois diferentes metais de adição (AWS ER 70 S – 6 e AWS E 110C-G-M). Para isso, corpos de prova deste aço ARBL e juntas soldadas desses dois metais de adição foram estudadas por meio de análises microestruturais, ensaios de tração uniaxial, microdureza e ensaios de fadiga por tração uniaxial. Os resultados mostraram que a velocidade de soldagem não causou alterações significativas na microestrutura do metal de solda e da zona termicamente afetada, na microdureza e na resistência à tração, quando foi utilizado o mesmo metal de solda. Porém, maiores velocidades de soldagem causaram o aumento do defeito de mordedura. Além disso, verificou-se um aumento da vida em fadiga do componente com a diminuição da velocidade de soldagem. Quando comparadas as amostras soldadas com uma mesma velocidade de soldagem, observou-se um aumento da proporção de ferrita acicular no metal de solda, um aumento da tensão de ruptura e, consequentemente, uma melhora da vida em fadiga do componente, em função do aumento da resistência mecânica do metal de solda. / Conselho Nacional de Desenvolvimento Científico e Tecnológico. / High strength and low alloy steels (HSLA) are attractive alternative in structural applications. Due to the low carbon and alloying elements (Ni, V and Ti) contents, HSLA steels show good levels of toughness and mechanical strength, besides good weldability, allowing use of lighter structural components, fuel economy, as well as the development of environmentally-friendly constructions and sustainable societies. The good combination of mechanical properties allows HSLA steels to be widely used in shipbuilding oil industry and automotive industry. For these applications, welding technology is inevitable, however it produces localized microstructural changes and reduction in the levels of mechanical strenght, residual stresses and undesirable defects, which generate potential problems of security and reliability. These welding defects accentuate the fatigue failure process when mechanical components are subjected to cyclic loads. In this work, the influence of the gas metal arc welding process (GMAW) on microstructure, mechanical properties and fatigue life of the HSLA DIN EN 10149 S700MC steel was studied, applying three welding speeds and two different addition metals (AWS ER 70 S-6 and AWS E 110C-G-M). For this purpose, samples of this HSLA steel and welded joints of these two addition metals were studied by microstructural analysis, uniaxial tension tests, microhardness tests and uniaxial tension fatigue tests. The results showed that the welding speed did not cause significant changes in the microstructure of the weld metal and of the heat-affected zone, in the microhardness and in the tensile strength, when the same weld metal was used. However, higher welding speeds caused the increase of the undercut defect. Besides that, an increase in fatigue life of the component with the decrease in welding speed was verified. When welded samples produced with the same welding speed were compared, an increase in the ratio of acicular ferrite in the weld metal zone, in the tensile stress and, consequently, an improvement in the fatigue life of the component was observe as a function of the increase in mechanical resistance of the weld metal.

Atlas Copco Secoroc AB are searching after new bulk materials for drill heads that are used in percussive drilling in order to improve their strength and durability. The aim of this project is to assist Atlas Copco in this search and provide them with further information regarding material properties, alloying elements, suppliers, etc. A literary study was carried out in order to identify materials that had UTS and KIC more than or equal to 1700 MPa and 70 MPa*m^1/2, respectively. Materials that fulfilled these criteria were T250 grade maraging steel, Cobalt free maraging steel, High cobalt maraging steel, 300 grade maraging steel, AerMet 100, AF1410, S53, M54, 300M, 4340M and PremoMet. These were categorized into maraging steels, high alloy secondary hardened steels, and low alloy steels, and were then further researched. The material with the highest combination of UTS and KIC was M54 followed by AerMet 100; while AF1410 had the highest KIC but a low UTS, and PremoMet had the highest UTS but a low KIC. Maraging steels and HASH steels have a similar price range, while low alloy steels are much cheaper.

Fatigue is one of the critical design aspects with immense significance where thefatigue life of a material can be stated as the number of cycles that a componentcan withstand under a particular type of loading without failure. The design processhas to include fatigue analysis in order to predict failure due to fatigue. This helpsin maintenance and servicing of a component reducing the chance of failure duringoperation of the component. Increased efficiency of predictive maintenance improvesthe life of the component.This thesis aims to study the relationship between the experimental, analytical andnumerical solutions of two high strength aluminium alloys and one steel alloy fortheir life in aircraft applications covering the effects of geometrical irregularities. Italso aims to answer convergence between the numerical and the analytical methodwhen compared with each other. The simulations are carried out for three materialsamong many used in aircraft and industrial applications (Al 7050-T7451, Al 7075-T6 and AISI 4340 Steel) for a pre-defined set of geometries. The stress field andthe stress concentration factor variations are also studied to identify their effects onfatigue life.The results from this work forms a strong background for the future research alongside SAAB or any other industries using these materials for their structures to findout the failure or predicting it accurately. Also, integral structures can be analysedin detail using this thesis as a base.

published_or_final_version / abstract / Civil Engineering / Master / Master of Philosophy

High strength, light weight and flexibility have made fabrics the preferred material for personal body armor and other impact protection applications such as passenger airbags, turbine blade containment systems, military and motorcycle helmets, and space debris shields. Recently, a shear thickening fluid has been used to treat a Kevlar fabric for an additional enhancement to the ballistic resistance of the neat fabric. Motivated by this technique of dissipation augmentation to high strength fabrics, this research aims at investigating the incorporation of other energy-dissipative materials into high strength fabrics. Specifically, two magnetic field-responsive materials (a magnetorheological fluid and Terfenol-D) have been used as a dissipation augmentation of Kevlar fabrics. No previous work has reported either experimental or computational research on the impact dynamics of Kevlar fabric treated with magnetorheological fluids or magnetostrictive solids. This research has investigated both computational modeling and experimental evaluation of the impact dynamics of textile composite armor, treated with magnetic field-responsive materials. Fragment simulating projectile impact tests have been conducted for the fabricated composite targets under an applied magnetic field. A computational model based on a hybrid particle-element method has been developed, to simulate the impact dynamics of composite fabric targets embodying magnetorheological fluids. This model is a mesoscale multiphysics model which can simulate impact dynamics including complex magneto-thermo-mechanical coupling effects as well as interactions among a projectile, fabric yarns, and magnetorheological fluid particles. Computer simulations have been performed to validate the hybrid particle-element method against experimental results. The computational method developed in this research has shown good agreement with the experimental data, in terms of the ballistic limit and residual velocity of a striking projectile. As fabric impact protection systems become more complex, and more expensive materials are introduced, computation may play a more important role in design. Therefore, the hybrid particle-element model in this dissertation may contribute to the improvement of the computational capability for virtual prototyping of fabric-interstitial fluid composites. / text

The current research has considered the characterization of the high strain rate constitutive response of three steels: a drawing quality steel (DDQ), a high strength low alloy steel (HSLA350), and a dual phase steel (DP600). The stress-strain response of these steels were measured at seven strain rates between 0. 003 s^-1 and 1500 s^-1 (0. 003, 0. 1, 30, 100, 500, 1000, and 1500 s^-1) and temperatures of 21, 150, and 300 ??C. In addition, the steels were tested in both the undeformed sheet condition and the as-formed tube condition, so that tube forming effects could be identified. After the experiments were performed, the parameters of the Johnson-Cook and Zerilli-Armstrong constitutive models were fit to the results. <br /><br /> In order to determine the response of the steels at strain rates of 30 and 100 s^-1, an intermediate rate tensile experiment was developed as part of this research using an instrumented falling weight impact facility (IFWI). An Instron tensile apparatus was used to perform the experiments at lower strain rates and a tensile split-Hopkinson bar was used to perform the experiments at strain rates above 500 s^-1 <br /><br /> A positive strain rate sensitivity was observed for each of the steels. It was found that, as the nominal strength of the steel increased, the strain rate sensitivity decreased. For an increase in strain rate from 0. 003 to 100 s^-1, the corresponding increase in strength at 10% strain was found to be approximately 170, 130, and 110 MPa for DDQ, HSLA350, and DP600, respectively. <br /><br /> The thermal sensitivity was obtained for each steel as well, however no correlation was seen between strength and thermal sensitivity. For a rise in temperature from 21 to 300 ??C, the loss in strength at 10% strain was found to be 200, 225, and 195 MPa for DDQ, HSLA350, and DP600, respectively for the 6 o?clock tube specimens. <br /><br /> For all of the alloys, a difference in the stress ? strain behaviour was seen between the sheet and tube specimens due to the plastic work that was imparted during forming of the tube. For the DP600, the plastic work only affected the work-hardening response. <br /><br /> It was found that both the HSLA350 and DDQ sheet specimens exhibited an upper/lower yield stress that was amplified as the strain rate increased. Consequently the actual strength at 30 and 100 s^-1 was obscured and the data at strain rates above 500 s^-1 to be unusable for constitutive modeling. This effect was not observed in any of the tube specimens or the DP600 sheet specimens <br /><br /> For each of the steels, both the Johnson-Cook and Zerilli-Armstrong models fit the experimental data well; however, the Zerilli-Armstrong fit was slightly more accurate. Numerical models of the IFWI and the TSHB tests were created to assess whether the experimental results could be reproduced using the constitutive fits. Both numerical models confirmed that the constitutive fits were applied correctly.

No description available.

[pt] Trata-se de um estudo experimental do comportamento de pilares de alta resistência submetidos à flexão composta reta e oblíqua. Foram ensaiados oito pilares com seção transversal de 25x15 cm e comprimento de 300 cm, compondo duas séries de 4 pilares cada uma. Na primeira série, a resistência do concreto foi de 40 MPa e os quatro pilares foram ensaiados à flexão composta oblíqua. Na segunda série, a resistência do concreto foi de 70 MPa e os quatro pilares foram ensaiados à flexão composta reta. Em cada série, a variável foi a taxa de armadura longitudinal que assumiu os valores 1,3%, 2,1%, 3,2% e 4,3%. A finalidade foi verificar os valores da excentricidade de segunda ordem que devem ser considerados no dimensionamento de pilares de concreto de alta resistência. Os resultados experimentais foram comparados com os obtidos pelos métodos do Pilar Padrão com Curvatura Aproximada e do Pilar Padrão com Rigidez Aproximada que constam na NBR 6118:2003. Essa comparação mostrou que o método da curvatura aproximada apresenta valores das excentricidades de 2ª ordem próximos dos reais no caso de pilares submetidos à flexão composta reta e oblíqua, enquanto que o método da rigidez aproximada é contra a segurança só na maioria dos ensaios de pilares submetidos à flexão composta reta. / [en] This work presents an experimental study of the behavior of slender high strength concrete columns under uniaxial and biaxial eccentric compression loads. Eight columns with cross-section of 15x25 cm and height of 300 cm were tested, divided into two series. In the first series, the concrete strength was 40 MPa and the four columns were tested under biaxial compression. In the second series, the concrete strength was 70 MPa and the four columns were tested under uniaxial compression. In each series, the variable was the longitudinal reinforcement ratio which assumed the values 1,3%, 2,1%, 3,2% e 4,3%. The objective was to verify the values of the eccentricity of second order that should be taken into account in the design of slender high strength concrete columns. The experimental results were compared with theoretical results obtained by the models of the approximated curvature and approximated stiffnes methods prescribed in the NBR 6118:2003 code. This comparison showed that the method of curvature approximate present values of the eccentricities of second order close to the real in the case of columns under uniaxial and biaxial eccentric compression loads, while the method of stiffness approximate is lower security in columns under uniaxial eccentric compression load.

L’objectif de cette thèse est d’aboutir à une meilleure compréhension des mécanismes de ségrégation du bore aux joints de grains austénitiques (γGB) et de leur effet sur la décomposition de l’austénite. En effet, l’addition de très faibles quantités de bore comme élément d’alliage permet d’augmenter de manière remarquable la résistance mécanique des aciers à très haute résistance. Cet effet est lié à l’état du bore aux γGBs qui décale la cinétique de décomposition de l’austénite.Tout d’abord, la distribution du bore dans la microstructure a été identifiée de manière très précise à l’aide des analyses de la même zone par Nano-SIMS et par MEB. De plus, le couplage de la sonde atomique tomographique et du Nano-SIMS a apporté une meilleure quantification de l’état du bore dans la microstructure. Ces études ont été réalisées après différents traitements thermiques qui ont été conçus spécifiquement pour étudier séparément chaque mécanisme. L’ensemble de ces résultats permet d’écarter la contribution de la ségrégation hors équilibre et confirme la présence d’un équilibre local entre les γGBs et la solution solide dans leurs voisinages. Par conséquent, le niveau de ségrégation du bore aux γGBs est contrôlé par l’état de précipitation des borures qui définit la concentration du bore en solution solide.Par ailleurs, des mesures de DRX in situ et de dilatomètrie ont été effectuées afin de suivre les cinétiques de formation de la bainite. Les résultats montrent que la cinétique de formation de la bainite est retardée en augmentant la quantité de bore ségrégé, par contre l’augmentation de la taille de grain austénitique l’accélère. / The aim of this thesis is to lead to a better understanding of the mechanisms of boron segregation at austenite grain boundaries (γGB) and its effect on the austenite decomposition. Indeed, the small quantity of boron as alloying element remarkably improves the mechanical resistance of the advanced high strength steels. This effect is related to the boron state at γGBs, which delays the kinetics of austenite decomposition.The boron distribution in the microstructure was precisely identified thanks to the analyses of the same field by using correlative nano-SIMS and SEM. In addition, the coupling of APT and nano-SIMS provided a better quantification of the boron state in the microstructure. These studies were performed after different heat treatments, which were specifically designed to study separately each mechanism. The results excludes the contribution of non-equilibrium segregation mechanism on boron segregation at γGBs and confirm the local equilibrium between the γGBs and the solid solution at the γGBs vicinity. Consequently, the level of boron segregation at γGBs is controlled by boride precipitation, which controls the concentration of boron in solid solution.Measurements of in situ XRD and the dilatometry were performed in order to follow the kinetics of bainite formation. The specific heat treatments were applied before bainite formation in order to study the effect of boron segregated amount at γGBs and the austenite grain size. These results show that the kinetics of bainitic transformation is delayed by the increase of boron segregated amount. Whereas, the increasing of austenite grain size accelerates the kinetics of bainitic transformation.