Nanocrystalline materials have generated immense scientific interest, primarily due to observations of significantly enhanced strength and hardness resulting from Hall-Petch grain size strengthening into the nano-regime. Unfortunately, however, most previous studies have been unable to present material strength measurements using established tensile tests because the most commonly accepted tensile test protocols call for specimen geometries that exceeded the capabilities of most nanocrystalline material synthesis processes. This has led to the development of non-standard mechanical test methodologies for the evaluation of miniature specimens, and/or the persistent use of hardness indentation as a proxy for tensile testing. This study explored why such alternative approaches can be misleading and revealed how reliable tensile ductility measurements and material strength information from hardness indentation may be obtained. To do so, an electrodeposition-based synthesis method to produce artifact-reduced specimens large enough for testing in accordance with ASTM E8 was developed. A large number of 161 samples were produced, tested, and the resultant data evaluated using Weibull statistical analysis. It was found that the impact of electroforming process control on both the absolute value and variability of achievable tensile elongation was strong. Tensile necking was found to obey similar processing quality and geometrical dependencies as in conventional engineering metals. However, unlike conventional engineering metals, intrinsic ductility (as measured by maximum uniform plastic strain) was unexpectedly observed to be independent of microstructure over the grain size range 10-80nm. This indicated that the underlying physical processes of grain boundary-mediated damage development are strain-oriented phenomena that can be best defined by a critical plastic strain regardless of the strength of the material as a whole. It was further shown that the HV = 3•σUTS expression is a reliable predictor of the relationship between hardness and strength for electrodeposited nanocrystalline materials, provided the material is ductile enough to sustain tensile deformation until the onset of necking instability. The widely used relationship HV = 3•σY was found to be inapplicable to this class of materials owing to the fact that they do not deform in an “ideally plastic” manner and instead exhibit plastic deformation that is characteristic of strain hardening behaviour.

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The strength of polycrystalline materials increases with decreasing grain size. The increase of strength is usually associated with deterioration of ductility, especially for materials having sub-micrometer or nanometer in grain size. It has bee suggested that the ductility of submicro- or nano- grained materials can be improved significantly by introducing a bimodal distribution of grain sizes. The purpose of the present study aims at clarifying the microstructural parameters of the bimodal distribution, such as area ratio and size difference, on the strength and ductility of pure nickel and nickel-cobalt specimens produced by electrodeposition. The microstructural parameters were determined from orientation imaging mapping technique using electron backscatter diffraction. Results indicated that the yield strength is mainly determined by the average size of the fine grains, whereas the tensile strength has a good relation with the average grain size in total. Moreover, it was showed that samples having a area ratio of the fine grains lower than 30% or higher than 70% possess a better ductility. The possible mechanism is discussed in detail.

Fiber reinforced polymers (FRPs) have gained increasing popularity in upgrades of reinforced structural elements due to high strength to weight ratio and ease of application. In this study, the effectiveness of the carbon reinforced polymer wrapping (CFRP) on ductility and strength of circular reinforced concrete columns, made of low strength concrete, is presented. Four circular reinforced columns with similar dimensions, longitudinal and confining steel reinforcement were tested under combined axial load and bending moment. Three specimens were strengthened with CFRP and the results were compared with the control specimen. The main parameter of the experimental study was selected as the level of eccentricity. First of all, the strain profiles of FRPs in the circumferential direction were observed and the confining stress distributions were examined. Then, an axial stress-strain model for FRP confined concrete with a transition from softening to hardening response for different confinement ratios is proposed. The proposed model was verified by comparing the model estimations with the test results obtained from this study and results reported by other researches. In addition, a parametric study was presented to obtain a simple equation to estimate curvature ductility of FRP confined circular columns.

A total of 47 lightweight aggregate concrete columns were constructed from four different types of lightweight aggregate and provided with different quantities of transverse reinforcement. The specimens were tested under a monotonically increasing level of compressive axial load. The rate of load application was varied from pseudo-static to the rate of dynamic loading expected during a major seismic excitation. The results from the experimental testing of the column members were used to derive a theoretical stress-strain model to predict the behaviour of lightweight aggregate concrete members under imposed loads. The stress-strain model was derived to predict the response of both lightweight aggregate and conventional weight concretes with compressive strengths up to and including 100 MPa. The model was calibrate against the experimental results obtained in this study and previously tested lightweight aggregate and conventional weight concrete columns. A series of pseudo-cyclic moment-curvature analyse were undertaking using the derived stress-strain model, to predict the behaviour of the lightweight aggregate concrete members when subjected to axial load and flexure. The results were compared to the confinement requirements in the potential plastic hinge regions of column elements required by the New Zealand Concrete Structures Standard, NZS3101: 1995. It was determined that the confinement requirements of NZS3101: 1995 were could be used to accurately determine the required quantity of transverse reinforcement for lightweight aggregate concrete members with a concrete density greater than 1700 kg/m3. A total of four lightweight aggregate concrete beam column subassemblies were constructed and tested under reversed cyclic lateral loading. The results from the specimen indicate that cyclic behaviour of the lightweight aggregate concrete was similar to conventional weight concrete. However the bond capacity between the longitudinal reinforcement and the surrounding concrete was weaker than previously tested conventional weight concrete members.

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Many intra-tectonic plate regions are considered to have low to moderate seismic risk. However, devastating earthquakes can occur in these regions and result in high consequences in terms of casualties and damage. Non-ductile detailing practice employed in these structures make them prone to potential damage and failure during an earthquake. Furthermore, the use of infill walls is a divisive issue as on positive side dual wall-frame systems have beneficial effects related to strength, stiffness, and ductility. However, if not designed properly infill wall can also lead to undesirable structural failures of complete wall frame system. Although, there has been significant amount of international research in this area, it is worth noting that very little research exists for Australian frames. This thesis presents the experimental and analytical research conducted at The University of Adelaide to gain some insight into the behaviour of typically detailed Australian reinforced concrete frames subjected to ground motions. The main objectives of this research were (1) to investigate the behaviour of non-seismically designed reinforced concrete frames under a 500-YRP earthquake; (2) to determine the different magnitudes of earthquake (YRP) that are likely to cause excessive drifts in or collapse of gravity-load-designed reinforced concrete frames and (3) to investigate the effect of infill walls on the moment-resisting frames subjected to seismic loads. The experimental program consisted of earthquake simulation tests on a 1/5 scale model of a 3-storey reinforced concrete frame and four ½-scale reinforced concrete brick infilled frame specimens subjected to quasi-static cyclic loading. The analytical study included static pushover and non-linear dynamic analyses of the 3-, 5- and 12-storey reinforced concrete frames. From the overall performance of gravity-load-designed bare reinforced concrete frames considered in this study, it was concluded that the non-seismically designed frames appear to be capable of resisting a “design magnitude earthquake” (i.e., 500- YRP) in low earthquake hazard regions. However, their behaviour under more severe earthquakes (e.g. a 2500-YRP earthquake) is questionable. Perhaps the earthquake design requirements should consider as an alternative the ‘collapse prevention’ limit state for longer return period earthquakes, of the order of 2000–2500-YRP. The experimental research on reinforced concrete infilled frame indicated that the infill wall does not adversely effect the in plane ultimate strength, stiffness, and ductility of the bare reinforced concrete frame. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1372229 / Thesis (M.Eng.Sc.) - University of Adelaide, School of Civil, Environmental and Mining Engineering, 2009

Este trabalho, realizado em cooperação com a Gerdau Riograndense, tem por finalidade avaliar o comportamento do aço GG1013-M, um aço baixo teor de carbono microligado com vanádio e manganês, na laminação a quente no que tange a sua resistência à deformação, possibilitando assim a tomada de decisão em relação a modificações no processo. Foram realizados testes em simulador termomecânico Gleeble™ para determinação das temperaturas a serem usadas no teste prático no laminador, onde testou-se lotes que cobrissem toda a amplitude da faixa de composição química da qualidade do aço em estudo. No teste prático no laminador, foram retiradas amostras para os ensaios mecânicos, onde identificou-se, por intermédio do tratamento de dados em software estatístico, a influência da variação dentro da faixa da composição química sobre os limites de escoamento e resistência. Como resultado, conseguiu-se determinar a faixa de temperatura mais provável, onde a resistência a deformação a quente é menor, minimizando ou eliminando as conseqüências da redução de ductilidade a quente por conta do endurecimento da matriz por precipitação dos elementos de liga em forma de compostos. / This work was conducted in cooperation with Gerdau Riograndense aiming at the evaluation of the hot rolling behavior of a low carbon steel microalloyed with manganese and vanadium (internally GG1013-M steel).The deformation resistance was evaluated, allowing for the decision in relation to changes in the process. A thermomechanical simulator GleebleTM was used to determine the temperatures to be used in practical tests in the rolling mill, where it was tested different material batches covering the large range of chemical compositions for this kind of steel. Mechanical tests were performed on samples taken from the practical tests in the rolling mill. From this tests the influence of chemical composition variation on the yeld strength and maximum stress was studied. As a result, we were able to determine the most likely range of temperatures for a minimization of hot strentgh, therefore also minimizing or eliminating the consequences of the reduction in the hot ductility due precipitation hardening of the matrix.

It was observed that the concrete is the most consumed material in the civil construction and not always satisfies all the demanded properties, its takes to researches that tries materials that can provide to the concrete more efficiency. This work, the discarding of residues procedures from the recycling of tires is focused, with the purpose to give to this material a rational destination, in the environment of the Civil Construction. The aim is to study the concrete behavior produced with rubber tire fiber addition, obtained by recycling of tire, and apply it on the confection of plates for to analyze the mechanical efforts behavior. The amongst of the additions are done in amongst usual for staple fibers. The bibliographical review disclosed that a reduction of the compressive strength when the rubber additions occurs. On the other hand, an increase of the ductility and the resistance for the impact occurs. The point of glow of the observed rubber was studied and it was observed that it occurs in a temperature range above of that one where the concrete has its deficit properties. With the short rubber fiber addition the same losses foreseen in literature without significant profits in the ductility are still verified. The rubber fibers chosen had been with low a relation length-diameter. This type for representing a small parcel and knowing that its separation can to add values that do not compensate its use as residue. Thus, it was considered that these results are satisfactory, a once that the possibility to include bigger rubbers fibers can increase the ductility. / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Observando-se que o concreto é o material mais consumido na construção civil e que nem sempre satisfaz todas as características exigidas, busca-se experimentar materiais que possam proporcionar a ele mais eficiência. Neste aspecto, com foco no descarte de resíduos provenientes da reciclagem de pneus, de forma a dar a este material um destino racional, no ambiente da Construção Civil, foi objetivo deste trabalho estudar o comportamento do concreto com adição de fibras de borracha produzidas na recauchutagem do pneu, aplicando à confecção de placas pré-moldadas para analisar o seu comportamento diante de esforços mecânicos. Os teores das adições foram aqueles usuais para fibras (1%, 2%, 3%). A bibliografia revelou que ocorre uma diminuição da resistência à compressão do concreto com tais adições, por outro lado, ocorre um aumento da tenacidade e da resistência ao impacto. Com a adição de fibras curtas, ou seja, com uma baixa relação comprimento/diâmetro, verificam-se ainda as mesmas perdas previstas na literatura sem ganhos significativos na tenacidade. Escolheu-se este tipo por representar uma pequena parcela e verificar se a sua separação poderia comprometer a sua utilização como resíduo. Foi estudado ainda o ponto de fulgor da borracha e observado que este ocorre em uma faixa de temperatura muito acima daquela em que o concreto tem suas propriedades ameaçadas. Considerou-se que estes resultados são satisfatórios, uma vez que a possibilidade de incluir fibras maiores pode aumentar a tenacidade e recuperar a perda observada.