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NiTiHf high temperature shape memory alloys are attractive due to their high operating temperatures (>100 oC) and acceptable transformation strain compared to NiTi. However, NiTiHf has limitations due to their lack of ductility and low strength, resulting in poor shape memory properties. In this study, Pd has been added to NiTiHf alloys in an attempt to improve their shape memory behavior. A combined approach of quaternary alloying and precipitation strengthening was used. The characterization of a Ni45.3Ti29.7Hf20Pd5 (at. %) polycrystalline alloy was performed in compression after selected aging treatments. Transmission electron microscopy was used to reveal the precipitation characteristics. Differential scanning calorimetry, load-biased (constant stress) thermal cycling experiments and isothermal stress cycling (superelasticity) tests were utilized to investigate the effects of aging temperature and time. The crystal structure and lattice parameters were determined from X-ray diffraction analysis. Significant improvement in the shape memory properties of Ni45.3Ti29.7Hf20Pd5 was obtained through precipitation strengthening. The effects of chemical composition (effects of Hf content replacing with Ti) on the shape memory properties of NiTiHfPd alloys were also revealed. Orientation dependence of the shape memory properties in aged Ni45.3Ti29.7Hf20Pd5 single crystals were investigated along the [111], [011] and [-117] orientations. The shape memory properties were determined to be strong functions of orientation and aging condition. A perfect superelastic behavior (with no irrecoverable strain) with 4.2 % recoverable compressive strain was obtained in the solutionized condition at stress levels as high as 2.5 GPa while 2 % shape memory strain under a bias stress of 1500 MPa was possible in an aged [111] oriented single crystal. A mechanical hysteresis of 1270 MPa at -30 oC, which is the largest mechanical hysteresis that the authors are aware of in the SMA literature, was observed along the [111] orientation. Finally, thermodynamic analyses were conducted to reveal the relationships between microstructure (e.g. precipitate size and interparticle distances) and martensitic transformations in Ni45.3Ti29.7Hf20Pd5 SMAs. Precipitate characteristics were found to be effective on the elastic energies for nucleation, propagation with dissipation energy and these energies influenced the TTs and the constant stress shape memory properties in Ni45.3Ti29.7Hf20Pd5 alloys.

Modern construction practices require proper knowledge to predict concrete pumping pressure, especially in high-volume and high-rise applications. Despite the progress made over the last decades, the spread of concrete pumping to high-rise construction has been hampered by the lack of standardized operating procedures and performance criteria. By and large, the guidelines available today focus predominantly on pumping Conventional Vibrated Concrete (CVC), while ambiguity still surrounds pumping Self-Consolidating Concrete (SCC) and other types of Highly-Workable Concrete (HWC). This PhD dissertation focuses on the fundamental principles relevant to the flow of high-strength SCC in pumping pipes, and it aims to develop methods to predict and reduce the required pumping pressure. The flow pattern of SCC in pipes is analytically investigated, providing a numerical approach to predict the pumping pressure based on the properties of both concrete and the lubrication layer, the pipe diameter, and the flow rate. The analytical results are further validated through full-scale pumping tests executed at the laboratory of the Université de Sherbrooke. Through this phase 26 optimal concrete mixtures were pumped in a 30-m pumping circuit to investigate the interactions between the concrete properties and pressure loss. The same tests are also employed to empirically correlate pressure loss with rheological and tribological properties of concrete at different flow rates. The resulting correlations furnish instrumental models capable of computing pressure loss for a wide range of concrete properties. In another application, the experimental results are analyzed to identify the influence of pumping on concrete properties with time. Full-scale pumping results are statistically analyzed in order to establish a quantitative description of the most influential parameters governing the concrete flow in pipes. As a result, concrete pipe flow is statically modeled, allowing the computation of pressure loss at different flow rates based on the the rheological and tribological properties of the concrete and the pipe diameter. Another statistical model is derived to calculate the pressure loss as a function of the V-funnel flow time, granting the advantage of predicting the pressure loss on job sites without the need for complex rheological and tribological measurements. In light of the research findings of the previous phases, a new simple test method called the pipe flow test (PFT) is developed in the context of this research, specifically for predicting pipe flow pressure loss. With preceding research phases as insights, the final stage of this project is directed toward mix design optimization faced with the challenge of reducing the pumping pressure and meeting the strength requirements of high-strength SCC. Ultimately, the research findings emanating from this investigation provide practical guidelines and conclusive models to predict and reduce pumping pressure for a wide scope of concrete mixtures and pipe diameters.

High strain rate plastic deformation of metals results in the formation of localized zones of severe shear strain known as adiabatic shear bands (ASBs), which are a precursor to shear failure. The formation of ASBs in a high-strength low alloy steel, namely AISI 4340, was examined based on prior heat treatments (using different austenization and tempering temperatures), testing temperatures, and impact strain rates in order to map out grain size and grain deformation behaviour during the formation of ASBs. In the current experimental investigation, ASB formation was shown to be a microstructural phenomenon which depends on microstructural properties such as grain size, shape, orientation, and distribution of phases and hard particles—all controlled by the heat treatment process. Each grain is unique and its material properties are heterogeneous (based on its size, shape, and the complexity of the microstructure within the grain). Using measurements of grain size at various heat treatments as well as dynamic stress-strain data, a finite element model was developed using Matlab and explicit dynamic software LSDYNA to simulate the microstructural deformation of grains during the formation of ASBs. The model simulates the geometrical grain microstructure of steel in 2D using the Voronoi Tessellation algorithm and takes into account grain size, shape, orientation, and microstructural material property inhomogeneity between the grains and grain boundaries. The model takes advantage of the Smooth Particle Hydrodynamics (SPH) meshless method to simulate highly localized deformation as well as the Johnson-Cook Plasticity material model for defining the behavior of the steel at various heat treatments under high strain rate deformation.The Grain Model provides a superior representation of the kinematics of ASB formation on the microstructural level, based on grain size, shape and orientation. It is able to simulate the microstructural mechanism of ASB formation and grain refinement in AISI 4340 steel, more accurately and realistically than traditional macroscopic models, for a wide range of heat treatment and testing conditions.

In the present work, the effect of variation in specimen orientation and heat treatment on the Stress Corrosion Cracking (SCC) susceptibility of 7050 aluminum alloy was investigated in 3,5% NaCl solution and under freely corroding conditions. For this purpose, Constant Extension Rate Tests (CERT) was performed on precracked Compact Tension (CT) specimens and the Direct Current Potential Drop technique was applied to measure the crack lengths. In addition to crack length versus time curves, the relationship between the crack growth rate and the stress intensity factor was determined. Fractographic analysis was utilized extensively to support the findings related with basic mechanisms of cracking. The alloy was found to be in the most susceptible state in the SL orientation, in which the crack propagation direction is parallel to the rolling direction. The resistance to SCC is higher in the TS but at maximum in LT orientation where the loading direction is parallel to the rolling direction. In the peak aging treatment, T651, alloy is susceptible to SCC in SL orientation. When the over aging treatment, T7651, is applied the resistance is increased and the two step over aging treatment, T73651, has resulted in an additional improvement in this orientation. On the other hand, the alloy showed higher resistance to SCC in TS and LT orientations in T651 condition compared to the T7651 and T73651 treatments. In these orientations, the alloy is less susceptible in T73651 condition than in T7651 treatment.

Concrete structures may be subjected to dynamic loading during their service life. Understanding the dynamic properties of concrete structures is becoming critical because of the increased concern about the dynamic loading of both civilian and military structures, and especially, the recent increase in terrorist attacks on structures. Fiber reinforced concrete (FRC) is known to exhibit superior performance in its post-peak energy absorption capacity, (i.e., toughness) under flexural and tensile loading. However, the behavior of fiber reinforced concrete under compressive impact has not previously been investigated. In the present research, the response of fiber reinforced concrete was investigated over the full strain rate regime, from static loading to high strain rate loading, and finally to impact loading. The compressive toughness of FRC under static loading was studied using an existing Japanese standard (JSCE SF-5). Then, a test method for FRC under compressive impact loading was developed, involving the use of a high speed video camera system to measure the deformation of FRC cylinders under compressive impact. The strain rate sensitivity of FRC in both flexure and compression was also fully investigated. FRC was found to have higher strengths under impact loading (both flexural and compressive) than under static loading. The compressive toughness under impact loading increased due to the high peak load and the high strain capacity. FRC under flexural impact loading showed a greater strength improvement than under static flexure. FRC displays a much higher Dynamic Improvement Factor (DIF) under flexural impact than under compressive impact. It gave an overall higher performance under impact than under static loading. It also exhibited a higher strain rate sensitivity than plain concrete in both compression and flexure. Damage analysis, in terms of loss of strain energy, was carried out based on damage mechanics principles. Damage was found to increase with increasing strain rate. A new constitutive model was proposed to account for the relationship between DIF (Comp) and strain rate and the data derived from the model were found to be consistent with the experimental results.

Thin-walled steel sections made from high strength thin cold-reduced G550 steel to Australian Standard AS 1397-1993 under compression are investigated experimentally and theoretically in this thesis. This thesis describes three series of compression tests performed on box-section stub columns, box-section long columns and lipped channel section columns cold-formed from high strength steel plates in 0.42 mm or 0.60 mm thickness with nominal yield stress of 550 MPa. The tests presented in this thesis formed part of an Australian Research Council research project entitled: Compression Stability of High Strength Steel Sections with Low Strain-Hardening. For the fix-ended stub column tests, a total of 94 lipped-square and hexagonal section stub columns were tested to study the influence of low strain hardening of G550 steel on the compressive section capacities of the column members. For the pin-ended long column tests, a total of 28 box-section columns were tested to study the stability of members with sections which undergo local instability at loads significantly less than the ultimate loads. For the fix-ended lipped channel section columns, a total of 21 stub and long columns were tested to study the failure resulting from local and distortional buckling with interaction between the modes. A numerical simulation on the three series of tests using the commercial finite element computer program ABAQUS is also presented as part of this thesis. The post-buckling behaviour of thin-walled compression members is investigated. The effect of changing variables, such as geometric imperfections and end boundary conditions is also investigated. The ABAQUS analysis gives accurate simulations of the tests and is in good agreement to the experimental results. Theoretical studies using finite strip methods are presented in this thesis to investigate the buckling behaviour of cold-formed members in compression. The theoretical studies provide valuable information on the local and distortional buckling stresses for use in the interaction buckling studies. The finite strip models used are the semi-analytical and spline models. As expected for the stub columns tests, the greatest effect of low strain hardening was for the stockier sections where material properties play an important role. For the more slender sections where elastic local buckling and post-local buckling are more important, the effect of low strain hardening does not appear to be as significant. The pin-ended and fix-ended long column tests show that interaction, which is between local and overall buckling in the box sections, and between local and distortional buckling in the open channel sections, has a significant effect on their member capacities. The results of the successful column tests and ABAQUS simulation have been compared with the design procedures in the Australian & New Zealand Standard for Cold-Formed Steel Structures AS&NZS 4600 and the North American Specification for Cold-Formed Steel Structural Members prepared by the American Iron and Steel Institute. The stub column tests show that the current design rules give too conservative predictions on the compressive section capacities of the column members; whereas the long column tests show that the current column design rules are unconservative if used in their current form for G550 steel. Three design proposals are presented in this thesis to account for the effects of high strength thin steels on the section and member capacities.

CAPES / O emprego de concreto em estruturas é bastante elevado em todo o mundo. Entretanto, o concreto convencional pode apresentar problemas relacionados com a durabilidade da estrutura, como o caso dos vazios de concretagem. O concreto autoadensável (CAA), vem se caracterizando como uma evolução do concreto convencional, pois apresenta vantagens como capacidade de preencher espaços, devido a auto adensabilidade, elimina falhas de concretagem e possibilita estruturas mais duráveis. Apesar dessas melhoras no estado plástico, no estado endurecido, as características do CAA se assemelham muito com as de um concreto convencional, ou seja, boa resistência à compressão, porém baixa resistência à tração e à fadiga. Assim, como forma de mitigar essas limitações, tem-se como evolução o emprego de concretos reforçados com fibras (CRF), os quais pela interferência da fibra atuando como costura nas fissuras presentes, resultam em compósitos, com melhor desempenho frente a esses esforços. Dentro desse contexto, a presente pesquisa analisou o desempenho de concretos autoadensáveis, com incorporação de fibras de aço, para que como resultado, fosse possível manter todas as melhoras ganhas no estado endurecido em suas propriedades mecânicas, sem que fossem perdidas as características de auto adensabilidade do CAA. Dessa forma, foram produzidas misturas, com diferentes tipos de fibras de aço (ancorada, corrugada e reta), com diferentes teores para cada tipo (0,4%, 0,8%, 1,2% e 1,5% em volume) e uma mistura de controle (sem adição de fibras), para então poder avaliar o comportamento do CAA quando incorporados diferentes tipos de fibras, com diferentes teores. A avaliação desse comportamento, se deu tanto no estado plástico do concreto, quanto no estado endurecido. Para as características no estado plástico, foram realizados os ensaios de espalhamento, t500 e Anel J. Para as propriedades no estado endurecido foram realizados ensaios de resistência à compressão axial, resistência à tração por compressão diametral, módulo de elasticidade. Além disso, buscou-se associar a resistência à fadiga do concreto, através de um ensaio não normatizado. Objetivando analisar a zona de transição, realizou-se o ensaio de microscopia eletrônica de varredura. Para analisar os resultados, foi necessário o emprego de tratamento estatístico, que avaliou a significância dos resultados. Os resultados mostram que foi possível manter a característica de auto adensabilidade do CAA para todos os teores de fibras empregados, e ainda obter ganhos, menos expressivos para resistência à compressão e de módulo de elasticidade, porém, resultados satisfatórios para resistência à tração e fadiga. / The use of concrete structures is fairly high throughout the world. However, conventional concrete can present problems related to the durability of the structure, as in the case of concrete voids. The concrete self compacting concrete (CAA), has been characterized as an evolution of conventional concrete, for advantages like ability to fill spaces through self adensabilidade eliminates concreting failures and enables more durable structures. Despite these improvements in the plastic state, in the hardened state, CAA characteristics closely resembling those of a conventional concrete, i.e., good compressive strength but low tensile strength and fatigue. Thus, in order to mitigate these limitations, we have to progress the use of reinforced concrete with fibers (CRF), which by the interference of the fiber acting as sewing in these cracks, result in composites with better performance against these efforts. In this context, the present study examined the self compacting concrete performance with the incorporation of steel fibers, so as a result, it was possible to keep all the improvements gained in the hardened state in their mechanical properties, without the self characteristics were lost adensabilidade CAA Thus, blends were produced with different types of steel fibers (anchored, and corrugated line), with different levels for each type (0.4%, 0.8%, 1.2% and 1.5% by volume ) and a mixture control (without fibers) and then to assess the CAA behavior when incorporated different types of fibers with different contents. The evaluation of this behavior occurred both in the plastic concrete state, as in the hardened state. For the characteristics in the plastic state, the scattering assays were performed, t500 and J. ring for the properties in the hardened state were performed resistance tests compressive, tensile strength by diametrical compression modulus. Furthermore, it sought to associate the fatigue strength of concrete, through a non-standardized assay. Aiming to analyze the transition zone, there was the scanning electron microscopy test. To analyze the results, employment was necessary statistical analysis, which evaluated the significance of the results. The results show that it was possible to maintain the characteristic of self adensabilidade CAA for all levels of employees fibers, and still obtain gains less significant compressive strength and modulus of elasticity, however, satisfactory results in tensile strength and fatigue.

Residual compressive stresses can be used to increase the lifetime of parts under cyclic stress as they negate the applied tensile stresses that cause crack initiation and propagation in the material. The goal of this project was to investigate methods to induce stresses, their advantages and disadvantages as well as depth and magnitude of induced stresses, and also to find methods of analyzing the induced residual stresses. This was done on behalf of Epiroc Drilling Tools AB in order for them to induce stresses on the insides of their long, narrow and hollow rods, where stress induction is difficult. Shot peening was used as a reference as that is the method currently in use by the company. The results show that the two most promising methods are cavitation peening and laser shock peening; two relatively new methods with large magnitudes and depth of induced stress as well as a great capability of inducing stresses on the hard-to-reach insides of the rods. Ultrasonic needle peening, ultrasonic shot peening as well as induction hardening, cryogenic treatment and friction stir processing were also investigated. Methods of analyzing the stresses include X-ray diffraction and slitting, hole drilling and ultrasonic methods.

A aplicação de chapas de aço como revestimento em matrizes de forjamento a quente tem sido estudada como uma alternativa inovadora, dentro de um projeto de cooperação internacional titulado “Evaluation of Sheet Metal Covers to Improve Tool Life in Forging”. Pesquisa realizada em parceria com a Alemanha pelo programa BRAGECRIM. Essas chapas serviriam como um metal de sacrifício em matrizes de forjamento a quente, que pretende substituir tratamentos superficiais de alto custo. As limitações geométricas e propriedades mecânicas das chapas garantiriam o sucesso ou não da gravura conforme o design exigido pela ferramenta, como também o número de ciclos de forjamento mantendo-se a integridade. Desta forma, o conhecimento das propriedades mecânicas em chapas e ductilidade torna-se fundamental para garantir os limites de aplicabilidade. Portanto, este trabalho tem como objetivo avaliar as propriedades mecânicas e os aspectos metalúrgicos em diferentes temperaturas de duas chapas de alta resistência DP600 e Hardox450®, os quais possuem diferentes microestruturas e ductilidade. Esta escolha se deve as diferentes aplicações que ambos os materiais possuem na indústria automobilística, devido as suas propriedades físicas, com a hipótese que influenciará na aplicação como máscaras que irão proteger as matrizes. Para isso foram realizados ensaios de dureza após ciclos de aquecimento e tração em diferentes temperaturas, com taxa de deformação controlada, simulando as condições térmicas que o material irá suportar durante o processo de forjamento. Para avaliar a ductilidade das chapas foi realizado o ensaio de estiramento biaxial. Uma análise pelo método de elementos finitos foi utilizada no ensaio de estiramento de punção esférico Erichsen, o qual foi possível pela análise de laboratório validar os experimentos e então a realização da simulação de estampagem de uma geometria bi radial em formato de copo. Os resultados de tração e dureza mostram que o DP600 possui considerável resistência mecânica em altas temperaturas com boa ductilidade, porém não maior que o Hardox450®, que perde em termos de ductilidade devido a fenômenos de fragilização em altas temperaturas. A simulação numérica permitiu avaliar como seria o produto estampado em uma geometria 3D, sobre os aspectos geométricos da chapa e os efeitos de anisotropia do DP600, como também suas tensões. / The application of sheet metal cover in hot forging dies has been studied as an innovative alternative, within an international project titled "Evaluation of sheet metal covers to improve tool life in forging". Research carried out in partnership with Germany under the BRAGECRIM program. The sheet metal would apply as a sacrificial membrane in the hot forging die, which intended to replace expensive surface treatments. The geometrical limitations and mechanical properties of the plates would guarantee the success or failure of the engraving according to the design required by the tool, as well as the number of forging cycles maintaining the integrity. In this way, the knowledge of the mechanical properties of the sheet metals and ductility becomes fundamental to guarantee the limits of applicability. Therefore, this work has as objective to evaluate the mechanical properties and the metallurgical aspects in different temperatures of two advanced High Strength Steel Sheets DP600 and Hardox450®, which have different microstructures and ductility. This choice is due to the different applications that both materials have in the automotive industry due to their properties, with the hypothesis that will influence the application as masks that will protect dies. Therefore, a hardness test has performed after heating cycles and tensile tests at different temperatures, with a controlled strain rate, simulating the thermal conditions that the material will withstand during the forging process. Biaxial stretching test to evaluate the ductility of the plates were performed. An inverse analysis by the finite element method was used in the Erichsen biaxial stretching test, in which it has been possible to validate the experiments and then to perform the stamping simulation of a bi-radial geometry in a cup format. The results show that the DP600 has considerable mechanical resistance at high temperatures with good ductility, but not higher than the Hardox450®, which is inferior in terms of ductility due to embrittlement phenomena at high temperatures. The numerical simulation allowed an evaluation of how the product can be stamped in a 3D geometry, the geometric aspects of the plate, the anisotropy effects of the DP600, as well as stress distributions.