Cold worked Cu-Fe-Cr alloys

The aim of this project was to investigate the properties of copper rich Cu-Fe-Cr alloys for the purpose of developing a new cost effective, high-strength, high-conductivity copper alloy. This paper reports on the influence of cold work. The age hardening response of the Cu-0.7%Cr-2.0%Fe alloy was minimal, but the resistance to softening was superior to that reported for any commercial high-strength, high-conductivity (HSHC) copper alloy with comparable mechanical and electrical properties. For example, an excess of 85% of the original hardness of the 40% cold worked alloy is retained after holding at 700 degreesC for 1 hour, whereas commercial HSHC Cu-Fe-P alloys have been reported to soften significantly after 1 hours exposure at less than 500 degreesC. The Cu-0.7Cr-2.0Fe alloy would therefore be expected to be more suitable for applications with a significant risk of exposure to elevated temperatures. Optical microscope examination of cold worked and aged microstructures confirmed the high resistance to recrystallization for Cu-0.7%Cr-2.0%Fe. The Zener-Smith drag term, predicting the pinning effect of second phase particles on dislocations in cold worked microstructures, was calculated using the precipitate characteristics obtained from TEM, WDS and resistivity measurements. The pinning effect of the precipitate dispersions in the peak-aged condition was determined to be essentially equivalent for the Cu-0.7%Cr-0.3%Fe and Cu-0.7%Cr-2.0%Fe alloys. A lower recrystallisation temperature in the Cu-0.7%Cr-0.3%Fe alloy was therefore attributed to faster coarsening kinetics of the secondary precipitates resulting from a higher Cr concentration in the precipitates at lower iron content. (C) 2001 Kluwer Academic Publishers.

Modelling the size of the crushed zone around a blasthole

A new model to predict the extent of crushing around a blasthole is presented. The model is based on the back-analysis of a comprehensive experimental program that included the direct measurement of the zone of crushing from 92 blasting tests on concrete blocks using two commercial explosives. The concrete blocks varied from low, medium to high strength and measured 1.5 in in length, 1.0 m in width and 1.1 m in height. A dimensionless parameter called the crushing zone index (CZI) is introduced. This index measures the crushing potential of a charged blasthole and is a function of the borehole pressure, the unconfined compressive strength of the rock material, dynamic Young's modulus and Poisson's ratio. It is shown that the radius of crushing is a function of the CZI and the blasthole radius. A good correlation between the new model and measured results was obtained. A number of previously proposed models could not approximate the conditions measured in the experimental work and there are noted discrepancies between the different approaches reviewed, particularly for smaller diameter holes and low strength rock conditions. The new model has been verified with full scale tests reported in the literature. Results from this validation and model evaluations show its applicability to production blasting. (C) 2003 Elsevier Science Ltd. All rights reserved.

Anaerobic ammonium oxidation by marine and freshwater planctomycete-like bacteria

Recently, two fresh water species, 'Candidatus Brocadia anammoxidans' and 'Candidatus Kuenenia stuttgartiensis', and one marine species, 'Candidatus Scalindua sorokinii', of planctomycete anammox bacteria have been identified. 'Candidatus Scalindua sorokinii' was discovered in the Black Sea, and contributed substantially to the loss of fixed nitrogen. All three species contain a unique organelle-the anammoxosome-in their cytoplasm. The anammoxosome contains the hydrazine/hydroxylamine oxidoreductase enzyme, and is thus the site of anammox catabolism. The anammoxosome is surrounded by a very dense membrane composed almost exclusively of linearly concatenated cyclobutane-containing lipids. These so-called 'ladderanes' are connected to the glycerol moiety via both ester and ether bonds. In natural and man-made ecosystems, anammox bacteria can cooperate with aerobic ammonium-oxidising bacteria, which protect them from harmful oxygen, and provide the necessary nitrite. The cooperation of these two groups of ammonium-oxidising bacteria is the microbial basis for a sustainable one reactor system, CANON (completely autotrophic nitrogen-removal over nitrite) to remove ammonia from high strength wastewater.

Variation of bulk properties of anaerobic granules with wastewater type

Development of a granular sludge with high strength, high biological activity and a narrow settling distribution is necessary for optimal operation of high-rate upflow anaerobic treatment systems. Several studies have compared granules produced from different wastewaters but these have largely been from laboratory-fed reactors or compared granules from full-scale reactors fed similar wastewater types. Though two authors have commented on the inferiority of granules produced by a protein-based feed, the properties of these granules have not been characterised. In this paper, granules from full-scale reactors treating fruit and vegetable cannery effluent, two brewery effluents and a pig abattoir (slaughterhouse) were compared in terms of basic composition, size distribution, density, settling velocity, shear strength, and EPS content. The results supported previous qualitative observations by other researchers that indicate granule properties depend more on wastewater type rather than reactor design or operating conditions such as pre-acidification level. The cannery-fed granules bad excellent shear strength, settling distribution and density. Granules from the two brewery-fed reactors had statistically the same bulk properties, which were still acceptable for upflow applications. The protein-grown granule had poor strength and settling velocity. (C) 2001 Elsevier Science Ltd. All rights reserved.

Estudo das propriedades dos adjuvantes na compatibilidade/robustez cimento/adjuvante

A qualidade do betão pode ser controlada pelo comportamento da fluidez da pasta de cimento, o qual está relacionado com a dispersão das partículas de cimento. Um dos maiores avanços na tecnologia do betão tem sido o desenvolvimento de aditivos. Um destes tipos de aditivos, os Superplastificantes (SP), fornecem a possibilidade de se obter uma melhor dispersão das partículas de cimento, produzindo pastas com elevada fluidez. Com o desenvolvimento de betões de alta resistência e elevado desempenho, os superplastificantes tornaram-se indispensáveis. Os superplastificantes são adsorvidos nas partículas de cimento e esta adsorção depende da composição do clínquer do cimento e do tipo de SP utilizado. Com a difusão do emprego dos aditivos redutores de água, têm surgido vários problemas de compatibilidade cimento/adjuvante. Esta investigação dedicada aos superplastificantes, fortes redutores de água, visou estudar quais as propriedades que poderiam influenciar a sua compatibilidade/robustez com o cimento. Também se procurou ganhar experiência com as técnicas analíticas de caracterização de adjuvantes. Assim, utilizou-se um tipo de cimento e dois tipos de superplastificantes (poli(étercarboxilatos) e poli(naftalenossulfonatos)) disponíveis no mercado português. Mantendo a mesma razão água/cimento (A/C), pretendeu-se determinar a natureza química, grau de funcionalização, teor e tipo de contra-ião, teor de sulfatos/sulfonatos do adjuvante e o comportamento dos superplastificantes nas pastas cimentícias, de forma a poder determinar indicadores de compatibilidade entre cimentos e superplastificantes. Constatou-se que a natureza química, o grau de funcionalização e a quantidade consumida dos superplastificantes têm influência nas pastas. Os indicadores de compatibilidade por parte dos superplastificantes parecem estar relacionados com o comprimento da cadeia lateral de éter e com o rácio CO2R/CO2 -. A alteração do momento da adição do adjuvante tem influência na compatibilidade cimento/adjuvante, sendo benéfico para os poli(étercarboxilatos) e prejudicial para o poli(naftalenossulfonato).

Influence of the use of recycled concrete aggregates from different sources on structural concrete

This paper intends to evaluate the capacity of producing concrete with a pre-established performance (in terms of mechanical strength) incorporating recycled concrete aggregates (RCA) from different sources. To this purpose, rejected products from the precasting industry and concrete produced in laboratory were used. The appraisal of the self-replication capacity was made for three strength ranges: 15-25 MPa, 35-45 MPa and 65-75 MPa. The mixes produced tried to replicate the strength of the source concrete (SC) of the RA. Only total, (100%) replacement of coarse natural aggregates (CNA) by coarse recycled concrete aggregates (CRCA) was tested. The results show that, both in mechanical and durability terms, there were no significant differences between aggregates from controlled sources and those from precast rejects for the highest levels of the target strength. Furthermore, the performance losses resulting from the RA's incorporation are substantially reduced when used medium or high strength SC's. (C) 2014 Elsevier Ltd. All rights reserved.

Drilling of fibre reinforced plastic laminates

The use of fibre reinforced plastics – FRP’s – in structures is under a considerable increase. Advantages of their use are related with their low weight, high strength and stiffness. The improvement of the dynamic characteristics has been profitable for aeronautics, automobile, railway, naval and sporting goods industries. Drilling is a widely used machining technique as it is needed to assemble parts in a structure. This is a unique machining process, characterized by the existence of two different mechanisms: extrusion by the drill chisel edge and cutting by the rotating cutting lips. Drilling raises particular problems that can reduce mechanical and fatigue strength of the parts. In this work, quasi-isotropic hybrid laminates with 25% of carbon fibre reinforced plies and 4 mm thickness are produced, tested and drilled. Three different drill geometries are compared. Results considered are the interlaminar fracture toughness in Mode I – GIc –, thrust force during drilling and delamination extent after drilling. A bearing test is performed to evaluate tool influence on the load carrying capacity of the plate. Results consider the influence of drill geometry on delamination. A correlation linking plate damage to bearing test results is presented.

Tool effects on hybrid laminates drilling

Fiber reinforced plastics are increasing their importance as one of the most interesting groups of material on account of their low weight, high strength, and stiffness. To obtain good quality holes, it is important to identify the type of material, ply stacking sequence, and fiber orientation. In this article, the drilling of quasi-isotropic hybrid carbon +glass/epoxy plates is analyzed. Two commercial drills and a special step drill are compared considering the thrust force and delamination extension. Results suggest that the proposed step drill can be a suitable option in laminate drilling.

In vitro assessment of three dimensional dense chitosan-based structures to be as bioabsorbable implants

Chitosan biocompatibility and biodegradability properties make this biopolymer promising for the development of advanced internal fixation devices for orthopedic applications. This work presents a detailed study on the production and characterization of three dimensional (3D) dense, non-porous, chitosan-based structures, with the ability to be processed in different shapes, and also with high strength and stiffness. Such features are crucial for the application of such 3D structures as bioabsorbable implantable devices. The influence of chitosan's molecular weight and the addition of one plasticizer (glycerol) on 3D dense chitosan-based products' biomechanical properties were explored. Several specimens were produced and in vitro studies were performed in order to assess the cytotoxicity of these specimens and their physical behavior throughout the enzymatic degradation experiments. The results point out that glycerol does not impact on cytotoxicity and has a high impact in improving mechanical properties, both elasticity and compressive strength. In addition, human mesenchymal stem/stromal cells (MSC) were used as an ex-vivo model to study cell adhesion and proliferation on these structures, showing promising results with fold increase values in total cell number similar to the ones obtained in standard cell culture flasks. (C) 2014 Elsevier Ltd. All rights reserved.

Utilização de algoritmos de processamento e análise de imagem na avaliação do dano em placas compósitas

PTDC/EME–TME/66207/2006 e POSC/EEA-SRI/55386/2004

Analyzing objects in images for estimating the delamination influence on load carrying capacity of composite laminates

The use of fiber reinforced plastics has increased in the last decades due to their unique properties. Advantages of their use are related with low weight, high strength and stiffness. Drilling of composite plates can be carried out in conventional machinery with some adaptations. However, the presence of typical defects like delamination can affect mechanical properties of produced parts. In this paper delamination influence in bearing stress of drilled hybrid carbon+glass/epoxy quasi-isotropic plates is studied by using image processing and analysis techniques. Results from bearing test show that damage minimization is an important mean to improve mechanical properties of the joint area of the plate. The appropriateness of the image processing and analysis techniques used in the measurement of the damaged area is demonstrated.

Mathematical modeling and simulation of heat flow through pultrusion die assembly system for thermoset composites

Pultrusion is an industrial process used to produce glass fibers reinforced polymers profiles. These materials are worldwide used when performing characteristics, such as great electrical and magnetic insulation, high strength to weight ratio, corrosion and weather resistance, long service life and minimal maintenance are required. In this study, we present the results of the modelling and simulation of heat flow through a pultrusion die by means of Finite Element Analysis (FEA). The numerical simulation was calibrated based on temperature profiles computed from thermographic measurements carried out during pultrusion manufacturing process. Obtained results have shown a maximum deviation of 7%, which is considered to be acceptable for this type of analysis, and is below to the 10% value, previously specified as maximum deviation. © 2011, Advanced Engineering Solutions.

Estudo de delaminação em compósitos de matriz polimérica

A aplicação do material compósito é neste momento bastante vasta, graças à combinação das suas características específicas, tais como, maior resistência específica e módulos específicos e melhor resistência à fadiga, quando comparados com os metais convencionais. Tais características, quando requeridas, tornam este material ideal para aplicações estruturais. Esta caminhada de sucesso iniciou desde muito cedo, quando o material compósito já era utilizado para fabrico de armas pelos mongóis e na construção civil pelos hebreus e egípcios, contudo, só a partir dos meados do século XX é que despertou interesses para aplicações mais modernas. Atualmente os materiais compósitos são utilizados em equipamentos domésticos, componentes elétricos e eletrónicos, passando por materiais desportivos, pela indústria automóvel e construção civil, até indústrias de grande exigência e visibilidade tecnológica como a aeronáutica, espacial e de defesa. Apesar das boas características apresentadas pelos materiais compósitos, no entanto, estes materiais têm tendência a perderem as suas propriedades quando submetidas a algumas operações de acabamento como a furação. A furação surge da necessidade de ligação de peças de um mesmo mecanismo. Os furos obtidos por este processo devem ser precisos e sem danos para garantir ligações de alta resistência e também precisas. A furação nos materiais compósitos é bastante complexa devido à sua heterogeneidade, anisotropia, sensibilidade ao calor e pelo facto de os reforços serem extremamente abrasivos. A operação de furação pode causar grandes danos na peça, como a delaminação a entrada, defeitos de circularidade do furo, danos de origem térmica e a delaminação à saída que se apresenta como o mais frequente e indesejável. Com base nesses pressupostos é que este trabalho foi desenvolvido de forma a tentar obter processos simples para determinação e previsão de danos em polímeros reforçados com fibras (de carbono neste caso) de forma a precavê-los. De forma a conseguir estes objetivos, foram realizados ensaios de início de delaminação segundo a proposta de Lachaud et al. e ensaios de pin-bearing segundo a proposta de Khashaba et al. Foram também examinadas extensões de danos de acordo com o modelo de Fator de delaminação ajustado apresentado por Davim et al. A partir dos ensaios, de pin-bearing, realizados foram analisadas influências do material e geometria da broca, do avanço utilizado na furação e de diferentes orientações de empilhamentos de placas na delaminação de laminados compósitos e ainda a influências dessas variáveis na força de rutura por pin-bearing. As principais conclusões tiradas daqui são que a delaminação aumenta com o aumento do avanço, o que já era esperado, as brocas em carboneto de tungsténio são as mais recomendas para a furação do material em causa e que a delaminação é superior para a placa cross-ply quando comparada com placas unidirecionais. Para a situação de ensaios de início de delaminação foram analisadas as influências da variação da espessura não cortada por baixo da broca/punção, de diferentes geometrias de brocas, da alteração de velocidade de ensaio e diferentes orientações de empilhamentos de placas na força de início de delaminação. Deste ensaio as principais conclusões são que a força de início de delaminação aumenta com o aumenta da espessura não cortada e a influência da velocidade de ensaio altera com a variação das orientações de empilhamento.

Estudo comparativo da resistência à tração de juntas adesivas de sobreposição simples e dupla

O método de união com ligações adesivas está cada vez mais a ser utilizado na conceção de estruturas mecânicas, por causa das vantagens significativas desta técnica em comparação com as ligações tradicionais. De facto, as juntas com ligação adesiva estão sob investigação intensa há bastante tempo. Entre as vantagens, destaca-se a redução de peso e possibilidade de unir diferentes materiais, incluindo compósitos, sem danificar as estruturas a ligar. Os adesivos comerciais variam desde resistentes e frágeis (por exemplo, Araldite® AV138) a menos resistentes e dúcteis (por exemplo, Araldite® 2015). Uma nova família de adesivos de poliuretano combina elevada resistência e ductilidade (por exemplo, Sikaforce® 7888). Este trabalho compara o desempenho à tração dos três adesivos supracitados, em juntas de alumínio (Al6082-T651) de sobreposição simples e dupla, com variação dos valores de comprimento de sobreposição (LO). A análise numérica de modelos de dano coesivo (MDC) foi realizada para analisar as tensões de arrancamento (oy) e as de corte (txy) na camada adesiva, para estudar a variável de dano do MDC durante o processo de rotura e para avaliar a capacidade MDC na previsão da resistência da junta. A análise da resistência e da variável de dano ajudou na compreensão das diferenças entre os adesivos no que se refere ao processo de rotura e resistência da junta. Observou-se que as juntas de sobreposição dupla apresentam uma distribuição de tensões bastante mais favorável relativamente às juntas de sobreposição simples, principalmente devido à eliminação da flexão do substrato interior. Como resultado, a resistência destas juntas foi tipicamente superior ao dobro da observada para as juntas de sobreposição simples, com exceção de algumas configurações de junta em que houve plastificação extensa ou mesmo rotura dos substratos por tração. O trabalho proposto permitiu também concluir que as previsões MDC são tipicamente precisas, e qual a família de adesivos é mais adequada para cada configuração de junta, com a clara vantagem para o Sikaforce® 7888. Como resultado deste trabalho, foram propostas diretrizes de conceção para juntas adesivas.