Дисертації з теми "AA2195"

The present work studies the microstructure and corrosion behaviour of 25 vol.% SiCp/AA2124-T4 metal matrix composites (MMCs) and AA2124-T4 aluminium alloy; and also the capability of excimer laser surface melting (LSM) to improve the corrosion resistance of the SiCp/AA2124 MMC and the monolithic alloy (MA). Microstructural characterization has shown significant influence of the presence and size of SiC particles on the fine Al2Cu precipitate and Mg segregation at SiC/Al interfacial regions. Such precipitates are revealed to be active sites for corrosion initiation in the MMCs, while the preferential sites for corrosion initiation in the MA are the coarse intermetallics. Corrosion evaluation performed in a 0.6 M NaCl solution suggests that the corrosion resistance of the MMC reinforced with micrometre-sized SiC particles is inferior to that of the MA and the MMC reinforced with submicrometre-sized SiC particles. The submicrometre-sized SiC particles have little adverse effect on the corrosion resistance of the MMC due to the reduced interfacial precipitates. Thin films of up to several micrometres have been achieved by excimer LSM on both the MMC and the MA. The surface roughness and the thickness of the melted layer increase with increasing laser fluence. High number of pulses (40 P) results in significant porosity in the MA and networks of cracking in the MMC. A homogeneous layer without chemical segregation except the Cu-rich segregation bands has been obtained on the MA; while complex microstructures are observed for the MMC, including the Cu-rich segregation bands, Al-Si eutectic structure and microsegregation-free structure laid in sequence from the bottom of the melted layer to the top surface. The modelling work suggest that the presence of SiC particles gives rise in high temperatures in the melt pool, which is useful to explain the materials responses upon laser irradiation, such as decomposition of SiC, evaporation of matrix alloy, and oxides formation. The fast cooling rate up to 1011 K/s is responsible for the formation of microsegregation-free structure. Corrosion evaluation has indicated improvement of corrosion resistance of the MMC and the MA after excimer LSM due to the reduction of the intermetallics. For the laser-melted MA, the corrosion behaviour is governed by the surface morphology and the porosity. The significant rippled structure obtained under high laser fluence could lead to crevice corrosion in the valley between the ripples whilst the pores could provide penetrating routes for the chloride solution to reach the Cu-rich segregation bands, leading to the delamination of the melted layer. For the laser-melted MMC, corrosion mainly initiated at the SiC remnants, which are rich in Si. The corrosion sites of the laser-melted MMC are in the form of small cracked blisters.

This thesis presents an analysis of data based on the results of a previous study into the path independence of friction stir welding (FSW). The original study was conducted in two phases using AA2024 and AA2198 aluminum alloy material. In Phase I, welds were made with six different tool designs, and tensile data was entered into Statgraphics® software as part of a design of experiments (DOE) approach for the purpose of optimizing the weld parameter process windows for each tool design. Phase II included a round robin study where welds were produced at four sites to evaluate site-to-site variability. In the present study, testing of the welds included additional tensile testing, full-field microhardness testing, and conductivity testing of the welds produced in the prior two phases of the program. The welds were inspected for defects, and the method of failure on the tensile specimens is discussed. Tensile data was evaluated statistically using Statgraphics® software. Previously, as part of Phase I, that data was evaluated using the techniques of chapter nine of the Metallic Materials Properties Development and Standardization (MMPDS), and design allowables were calculated at that time. In the present study, Phase II data was compared using the design allowables from Phase I. Variability was not found to be significant when evaluated according to location of the tensile coupon along the weld joint line or as a function of weld parameters in the process window. Although site-to-site variability was significant, it was low, with the highest variation for each material being 2 to 5.5 ksi. No significant outliers were identified. There is evidence that the friction stir welding process is path-independent and that a defect-free weld is uniform in tensile strength from beginning to end. There is also evidence that a DOE approach can be used to optimize the weld parameter process window for any tool in order to identify a range of weld parameters where a defect-free weld can be produced.
Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Mechanical Engineering.

The effect of individual and combined zirconium and manganese additions have been compared for an AA2198 6 mm thick sheet in T351 temper regarding their influence primarily on recrystallisation resistance and secondly on fracture toughness and overageing resistance. A complete characterisation of the dispersoid distributions was carried out for a deeper understanding of the effects of the Al3Zr and Al20Cu2Mn3 particles, involving studying their formation from the as-cast and homogenised stage.The most important finding in this work was the lower recrystallisation resistance in the alloy containing 0.1 wt%Zr + 0.3 wt%Mn compared to that containing only 0.1 wt%Zr. This result was rather unexpected, if one considers the opposite microsegregation patterns of Zr and Mn during casting, which leads to dispersoids occupying the majority of the grains’ volume and minimising dispersoid-free zones that could be potential sites for nucleation of recrystallisation. The other two alloys with dispersoid additions 0.05 wt%Zr + 0.3 wt%Mn and 0.4 wt%Mn, were partially and fully recrystallised respectively in the rolled T351 condition.Equally important in this work, was the observation that the opposite microsegregation trend of Zr and Mn sufficed to restrict grain growth in unrecrystallised areas. The 0.1Zr-0.3Mn alloy exhibited the lowest grain size of all alloys, both in the T351 temper and after annealing at 535oC for up to 144 hours. The reason for this was the combined action of Al20Cu2Mn3 dispersoids and Mn solute in the regions where the Zr concentration was low (i.e. near the grain boundaries), which offered additional pinning pressure to those areas compared to the 0.1Zr alloy.The lower recrystallisation resistance of the 0.1Zr-0.3Mn alloy was explained on the grounds of two main factors. The first was the lower subgrain size and hence stored energy within bands of Al20Cu2Mn3 dispersoids, which increased the driving force for recrystallisation in these regions. The second was the interaction between Zr and Mn that led to a decrease in the Al3Zr number density and pinning pressure. Since Zr was the dominant dispersoid family in terms of inhibiting recrystallisation, inevitably this alloy became more prone to recrystallisation. The Al3Zr pinning pressure was found to be much lower especially within bands of Al20Cu2Mn3 dispersoids. The detrimental effect of the Mn addition on the Al3Zr distribution was proven not to result from the dissolution of Zr within Mn-containing phases, and several other phases, at the grain interior and also in grain boundaries. The observed effect could not be precisely explained at this stage.Concerning mechanical properties, the 0.1Zr alloy exhibited the best combination of properties in the Kahn tear tests for fracture toughness. Further, it had a higher overageing resistance compared to the 0.1Zr-0.3Mn alloy.As an overall conclusion from this work, considering all the studied properties here that are essential for damage tolerant applications, the addition of 0.1 wt%Zr to the AA2198 6 mm thick sheet was found to be superior to that of the combined addition of 0.1 wt%Zr + 0.3 wt%Mn.

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Universidade Federal de Sao Carlos
Friction Stir Welding (FSW) process, conceived in 1991, has been the target of research in the last decades due to the excellent properties presented by its welded joints, favored by the fact of occurrence in the solid state, and easiness of application, enabling several weld geometries. In particular, metal alloys with low melting points, in which conventional methods of welding (based in fusion) are hard to apply, have been benefited by this method, with large application in automobilist and aerospace industrial sectors. These branches enterprises are interested in determining the set of parameters that will yield the best mechanical properties, before utilizing FSW in commercial scale. With this objective in mind, this work aimed at optimizing the FSW parameters in the Aluminum Alloy 2198-T851, considering geometry of plates of different thicknesses (tailor welded blanks configuration). Due to the asymmetric characteristic of the welded joints, welding parameters related to positioning of the welding tool (welding angles and pin offset) were varied, in two groups of plates of different thicknesses: 4.2-3.5 milimeters, and 4.2-2.5 milimeters. Results obtained from macro and microstructural characterization (optical microscopy), tension tests and microhardness analyses were considered as criteria for determining the best quality welds. After the analysis of these results and correlation with related literature, it was concluded that the proposed variation in welding parameters affects the flux of material in the welded joint, possibly leading to formation of defects, causing a detrimental effect on the mechanical properties. Nevertheless, welds with mechanical properties equal to or superior to the base metal were obtained (except for elongation values), especially in relation to yield stress values, of capital importance in industrial sectors associated with high security demands, such as automobilist and aerospace.
O processo de soldagem por fricção e mistura (FSW), concebido em 1991, tem sido alvo de pesquisas nas últimas décadas em função das boas propriedades apresentadas em suas juntas, favorecidas pelo fato do processo ocorrer no estado sólido, e em função da facilidade de aplicação, possibilitando diversas geometrias de solda. Em especial, ligas metálicas com baixo ponto de fusão, de difícil soldabilidade por métodos convencionais (baseados em fusão) têm sido beneficiadas por este método, com larga aplicação nos setores industriais automobilístico e aeroespacial. Interessa, às indústrias destes ramos, a determinação dos conjuntos de parâmetros que resultarão nas melhores propriedades mecânicas possíveis, anteriormente à utilização comercial de larga escala deste novo processo. Com este objetivo foi realizada a otimização dos parâmetros de soldagem por FSW em liga de alumínio 2198-T851, aplicada em configuração de chapas de diferentes espessuras (tailor welded blanks). Devido à característica assimétrica da junta soldada, variaram-se os parâmetros de soldagem relacionados ao posicionamento da ferramenta (ângulos de soldagem e deslocamento transversal do pino), em dois conjuntos de chapas de diferentes espessuras: 4,2-3,5 mm, e 4,2-2,5 mm. Como critérios para determinação da solda de melhor qualidade foram considerados os resultados obtidos de caracterização macro e microestrutural (microscopia ótica), ensaios de tração e de microdureza. Após análise dos resultados e correlação com a literatura, concluiu-se que a variação dos parâmetros de soldagem considerados afeta o fluxo de material na junta soldada, podendo levar à formação de defeitos, causando efeito detrimental sobre as propriedades mecânicas das soldas. Obtiveram-se, também, soldas com desempenho mecânico igual ou superior ao do metal base (com exceção do alongamento total na ruptura), sobretudo em relação a valores de tensão de escoamento, cuja importância é significativa em setores com alta exigência de segurança, como são o automobilístico e o aeroespacial.

A busca por uma plataforma mais eficiente ée uma importante estratégia na manutenção da competitividade na indústria aeronáutica. Mais especificamente na aviação comercial, a busca por estruturas mais leves, resistentes e de fácil manutenção ée a tradução desta eficiência desejada. Neste cenário, novos materiais com propriedades cada vez mais otimizadas desempenham um papel fundamental. As ligas de alumínio contendo lítio surgiram há algumas décadas; porém, ainda hoje, sua aplicação ée restrita. Com uma superioridade marcante em alguns aspectos em relação às ligas de alumínio convencionais mais utilizadas atualmente, esta classe de ligas apresenta algumas particularidades, por exemplo, custo, gestão das sobras e algumas propriedades específicas, que truncaram seu uso extensivo na indústria aeronáutica. Foram necessárias décadas de aperfeiçoamento na composição de elementos de liga e tratamentos térmicos e termomecânicos para que hoje estivessem disponíveis algumas ligas da chamada terceira geração, nas quais muitos destes problemas foram mitigados. Ainda assim, são grandes os desafios para a introdução desta classe de ligas em uma aeronave, desde a fase de projeto atée a estratégia de mercado para a compra e gestão de peças de reposição. Dentro deste contexto, o presente trabalho avaliou a aplicação da liga AA2198 de alumínio-lítio da terceira geração para aplicação em revestimentos de fuselagem de aeronaves, em substituição à liga AA2024. Foram considerados aspectos de projeto, avaliadas as propriedades mecânicas e realizadas operações de conformação plástica por estiramento utilizando-se chapas de 1,6 mm de espessura, concluindo-se que, nestes aspectos, a liga AA2198 pode substituir com vantagens a liga AA2024 devido a um conjunto superior de propriedades mecânicas e um comportamento similar em condições de processamento para obtenção de peças conformadas.

This research demonstrates the use of friction stir welding (FSW) to join dissimilar (Al-Mg) metal alloys. The main challenges in joining different, dissimilar metal alloys is the formation of brittle intermetallic compounds (IMCs) in the stir zone affecting mechanical properties of joint significantly. In this present study, FSW joining process is used to join aluminum alloy AA2139 and magnesium alloy WE43. The 9.5 mm thick plates of AA2139 and WE43 were friction stir butt welded. Different processing parameters were used to optimize processing parameters. Also, various weldings showed a crack at interface due to formation of IMCs caused by liquation during FSW. A good strength sound weld was obtained using processing parameter of 1200 rev/min rotational speed; 76.2 mm/min traverse speed; 1.5 degree tilt and 0.13 mm offsets towards aluminum. The crack faded away as the tool was offset towards advancing side aluminum. Mostly, the research was focused on developing high strength joint through microstructural control to reduce IMCs thickness in Al-Mg dissimilar weld joint with optimized processing parameter and appropriate tool offset.

Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, December 2007.
Thesis Advisor(s): McNelley, Terry. "December 2007." Description based on title screen as viewed on January 22, 2008. Includes bibliographical references (p.45). Also available in print.

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Universidade Federal de Sao Carlos
Aluminum alloys have low density and high corrosion resistance, and because of that this alloys are being increasingly used in aircraft industry. However, a downside of this alloys is its weldability in fusion process, which can generate defects such as H2`s porosity and formation of high temperatures cracks limiting its applicability. Seeking an alternative process, it was developed a solid state welding process called Friction Stir Welding - FSW. The main advantage of this process is that welding occurs at a temperature below the melting temperature of the material, eliminating defects from solidification. Since its invention, the FSW gets world attention, because structural alloys with difficult weldability showed excellent results metallurgical and mechanical after welding. Therefore, in this study the aluminum alloy AA2139 was welded by FSW, a structural alloy with a high potential for aerospace applications due to good combination of strength and fatigue and fracture toughness. Thus, it was evaluated the mechanical and metallurgical behavior of aluminum alloy AA2139 under different conditions of heat treatment, T3 and T8. The microstructural features were investigated using optical and electron microscopy (SEM and TEM) as well as the mechanical behavior was determined by bending testing, microhardness profiles, conventional tensile testing (including system analysis of deformation - ARAMIS) and tensile testing using micro-samples and also the temperature measurements were performed during welding. The results showed that welds in alloy AA2139-T3 and AA2139-T8 may show different results, even using the same tool and the same welding parameters. Moreover, the temperature reached during welding affects the precipitation in the welded region which determines the performance of the weld.
As ligas de alumínio apresentam baixa densidade e alta resistência à corrosão, por isso estão sendo cada vez mais utilizadas nas indústrias aeronáuticas. No entanto, as ligas de alumínio podem gerar defeitos como porosidade por H2 e formação de trincas a altas temperaturas em processos de soldagem que envolve fusão, limitando a sua aplicabilidade. Visando um processo alternativo, foi desenvolvido um processo de soldagem no estado sólido denominado Friction Stir Welding - FSW. A principal vantagem deste processo é que a soldagem ocorre a uma temperatura abaixo da temperatura de fusão do material, o que elimina defeitos provenientes da solidificação. Desde a sua invenção, o FSW obtém atenção mundial, já que ligas estruturais de difícil soldabilidade apresentaram excelentes resultados metalúrgicos e mecânicos após a soldagem. Por este motivo, neste estudo foi soldado por FSW a liga de alumínio AA2139, uma liga estrutural com alto potencial para aplicações aeroespaciais devido à boa combinação entre resistência mecânica e a fadiga e tenacidade a fratura. Para tanto, foram avaliados o comportamento mecânico e metalúrgico desta liga de alumínio AA2139 em condições diferentes de tratamento térmico, T3 e T8. Os aspectos microestruturais foram investigados usando-se de microscopia ótica e eletrônica (MEV e MET), assim como o comportamento mecânico foi determinado através de ensaios de dobramento, perfis de microdureza, ensaio de tração convencional (incluindo sistema de análise de deformação - ARAMIS) e ensaio de tração usando-se micro-amostras e por fim medições de temperatura foram realizadas durante as soldagens. Os resultados obtidos mostraram que soldas na liga AA2139-T3 e AA2139-T8 apresentam resultados distintos, mesmo utilizando a mesma ferramenta e os mesmos parâmetros de soldagem. Além disso, a temperatura atingida durante a soldagem influencia a precipitação na região soldada a qual determina o desempenho da solda.

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A garantia da integridade estrutural dos equipamentos na indústria passa necessariamente pela determinação das condições dos materiais e de suas propriedades mecânicas. Hoje em dia exigem-se materiais com propriedades específicas que deixam de ser atendidas pelo uso isolado das ligas metálicas, cerâmicas e poliméricas. Temos como exemplo casos como os da indústria eólica, aeronáutica, náutica e de transporte que, necessitam de materiais com baixa densidade, resistentes a corrosão, resistentes ao impacto e rígido. Nesta linha de pensamento, cada vez mais pesquisadores estão investindo tempo e tecnologia em busca de matérias compósitos que garantam uma distribuição homogênea de fases no seu reforço. A Metalurgia do Pó (MP) vem se destacando na promoção de uma melhor distribuição do reforço na matriz em relação ao processo convencional de fundição, obtendo-se então materiais com melhores propriedades mecânicas, dureza e resistência ao desgaste. O objetivo principal desse trabalho é produzir compósitos de matriz de liga de alumínio AA 2124, reforçado por nitreto de silício (Si3N4), utilizando o processo de metalurgia do pó (MP) e técnica de moagem de alta energia. Para tanto utilizou-se a caracterização por microscopia ótica (MO), microscopia eletrônica de varredura (MEV), difração de raios X (DRX), espectroscopia por dispersão de energia (EDS), difração a laser para avaliar e comparar as características de cada compósito, além de verificar as propriedades mecânicas inerentes. Os resultados de dureza apresentaram-se linearmente crescentes com o aumento da fração de reforço na matriz.

Thesis (M.S.)--University of Akron, Dept. of Mechanical Engineering, 2007.
"December, 2007." Title from electronic thesis title page (viewed 02/23/2008) Advisor, T. S. Srivatsan; Faculty readers, Craig Menzemer, Amit Prakash; Department Chair, Celal Batur; Dean of the College, George K. Haritos; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.

Acoustics is the study of all sound waves, with ultrasound classified as those frequencies above 20,000 Hz. Currently, ultrasound is being used in many industries for a variety of purposes such as ultrasonic imaging, ultrasonic assisted friction stir welding, and ultrasonic spot welding. Despite these uses, the effects of ultrasound on phase stability and resultant mechanical properties has been minimally analyzed. Here we study the impact waves play in ultrasonic welding and design an apparatus to maximize waves entering aluminum alloy samples. Aluminum 2139 and 7050 are used because they are precipitation strengthened by metastable phases so temperature change, and the corresponding phase stability, can greatly impact their strength. Results suggest that the ultrasonic welder primarily imposes a localized temperature spike due to friction, averaging over 200°C in a few seconds, which generally lowers the Vickers hardness due to coarsening or even dissolution of strengthening precipitates. Conversely, the new design increases the Vickers hardness by up to 30% over the initial hardness of approximately 63HV for aluminum 2139 and 83HV for aluminum 7050, respectively, while only increasing the temperature by an average of approximately 10°C. This new design was unable to achieve peak hardness, but the strengthening it achieved in two minutes was equivalent to one month of natural aging. If this system was able to be fine-tuned, it could serve as a quick strengthening process for recently weakened aluminum alloys, such as after friction stir welding.

The polymerisation of dithienylethylenes (cis and trans 1,2-di(3-thienyl) ethylene, DTE-cis and DTE-trans), thiophene dithiolenes (4,5-dithiophen-3-yl-[1,3] dithiol-2-one, Th-3,3,4,5-di-thiophen-2-yl-[1,3]dithiol-2-one, Th-2,2,4-thiophen-3- yl-5-thiophen-2-yl-[1,3]dithiol-2-one, Th-2,3 and 4,5-di-(5-methyl-thiophen. -3-yl)- [1,3]dithiol-2-one, Th-3,3Me), and nickel dithiolenes (bis[1,2-di(3-thienyl)-1,2-ethenedithiolene] nickel tetrafluoroborate, Ni(Th-3,3)2 and bis[1,2-di(2-thienyl)-1,2-ethenedithiolene] nickel tetrafluoroborate, Ni(Th-2,2)2) was carried out and the resultant polymers were analysed by electrochemical and spectroelectrochemical methods. The voltammetric behaviour of the electropolymerised PDTE-cis and PDTEtrans suggested that polarons and bipolarons were produced upon oxidation. Nevertheless, the formation of a conducting state was not observed in the SNIFTIRS measurements. Upon I2 chemical doping, PDTE-cis and PDTE-trans showed increased stability in the doped state and the SNIFTIRS response of PDTE-trans, revealed similar IR characteristics to those of conductive polymers. The voltammetric and IR behaviour of the dithiolenes, PTh-3,3, PTh-2,2 and PTh-2,3 was similar to that of many conducting polymers. From the UV-Visible spectra of the neutral films it was determined that PTh-3,3, PTh-2,2 and PTh-2,3 have a bandgap of 2.04,2.30 and 2.18 eV, respectively. The electrochemical and SNIFTIRS results for PTh-3,3Me were noticeably different from the other dithiolene polymers revealing a poorly conductive polymer. The solid-state modification of PTh-3,3 to produce a new TTF derivatised polythiophene was carried out. The inclusion of TTF into the PTh-3,3 film was confirmed by voltammetry and IR data that also suggested that only partial modification of the polymer had occurred. The voltammetry of polyNi(Th-3,3)2 and polyNi(Th-2,2)2 showed a redox couple attributed to the electrochemistry of the nickel dithiolene centre, confirming the incorporation of the metal complex into the polymer. Whilst the SNIFTIR spectra of polyNi(Th-3,3)2 showed the characteristic features of metal dithiolenes, the IR behaviour of polyNi(Th-2,2)2 was more comparable to that of conducting polythiophenes. This result indicates that charge delocalisation in polyNi(Th-2,2) occurs through the Ni dithiolene sites disrupting the typical electroactivity of the dithiolene unit. For the polyNi(Th-3,3)2 films, the nickel dithiolene sites seem to be electronically isolated, preserving the aromaticity of the dithiolene system.

Background & Aims: The 'high-density lipoprotein (HDL) hypothesis', that therapeutic interventions directed at raising HDL cholesterol might translate into improved cardiovascular outcomes, has been confounded by recent reports from genetic and pharmacological studies. HDL functionality may be more important than cholesterol cargo. HDL cholesterol levels are normal or even high in Type 1 Diabetes (T1DM) but do not seem to protect against atherosclerosis as might be expected; this thesis aims to offer new insight into HDL functionality through examination of these patients. This thesis also aims to improve understanding of the qualitative changes in lipoproteins associated with diabetes and increased cardiovascular morbidity, with emphasis on atherogenic modifications of apolipoprotein B and sphingolipids, and consideration of the relationship between these changes, novel and established biomarkers, and macrovascular and microvascular diabetic complications. Materials & Methods: Patients with Type 1 (n = 91) and Type 2 (n = 40) Diabetes Mellitus and healthy volunteers (n = 104) attended for fasting blood tests, urinalysis, and examination including cardiac computed tomography, carotid doppler studies and assessments of nerve function. In vitro studies of lipoprotein modification used pooled human plasma. Results: Lipoprotein glycation represents an atherogenic modification. In vitro glycation occurs more readily in the presence of physiological concentrations of copper. HDL and copper-selective chelation with triethylenetetramine prevents glycation. Glycated apolipoprotein B, oxidized LDL and small-dense LDL levels were significantly higher in T1DM; HDL cholesterol levels were also significantly higher, but with altered apolipoprotein distribution, and significantly lower cholesterol efflux capacity and PON1 activity than in healthy controls. Significant changes were also observed in cystatin C, advanced glycation end-products, leucine-rich alpha-2-glycoprotein, lipoprotein-associated phospholipase A2, a variety of inflammatory markers, and sphingolipid and ceramide profiles. Discussion: Cardiovascular disease is the leading cause of death and disability in diabetes. Patients with diabetes show qualitative and kinetic lipoprotein abnormalities, and any cardiovascular benefit associated with intensive glucose lowering may be related to effects on lipoprotein metabolism rather than directly through altered glycaemia. The apparently relatively undisturbed lipid profile observed in many patients with diabetes hides major atherogenic changes and altered HDL functionality, which may be at least partially responsible for the persistent increased risk of cardiovascular disease in patients with diabetes. HDL-based therapy remains a largely unfulfilled promise, but there may be a role for copper-selective chelation and more aggressive low-density lipoprotein lowering in the reduction of diabetic complications.

Recruitment is a mission-critical process for human resources management. Due to the high turnover rate and lack of specific skill requirements, the retail sector has an acute need to hire new employees to fill vacancies. Therefore, recruiting a relatively large number of new employees in a limited period of time is crucial for companies in the retail industry. Existing studies have suggested that by designing recruitment activities and utilising appropriate recruitment sources to promote and announce a job, employers are able to attract jobseekers to apply for jobs and join the organisation. The social communication theory highlights four major elements involved in any information communication: the information communicator (source), the information receiver (audience/jobseeker), the response (the receiver’s attitude towards the information received and the decision taken to apply or not) and the stimulus (the message/information content that is transmitted by the communicator). An individual’s ‘attitude’ towards the recruitment information can significantly affect their ‘intention’ of making a job application decision, and this intention can significantly influence their actual decision-making ‘behaviour’, such as accepting a job offer. Consequently, most of these studies focus on the effectiveness of the stimulus (e.g., how the design of the recruitment information content can attract more jobseekers).However, there are divergent results in the literature. For instance, numerous researchers have attempted to investigate how different recruitment information sources can impact jobseekers’ application and recruitment decisions. Some researchers claim that the formal, company-controlled, recruitment information sources, such as advertising and corporate websites, are less effective than informal. By contrast, other researchers indicate that formal sources are used and accepted more often by jobseekers because this information is regarded as considered to be more objective and reliable than the experience-based route (e.g., word-of-mouth). Some researchers suggest that employers should provide objective, hard information (confirmable information such as salary and location) and provide the message in the employer’s tone’ using company-controlled sources; thereby not to convey too much soft, experience-based information from employees. Only very limited research has considered the influences of receiver’s differences (individual differences) on the stimulus (content) and communications (source) as a moderator. The receivers’ differences could be the essential information that can be used to interpret the divergent findings in the literature. Psychologists have demonstrated that individual differences will influence personal values and will be translated into personal preferences. Decision-making research suggests that every decision-making process involves individuals’ decision habits and preferences. People tend to keep their decision habits and preferences throughout different decisions. Therefore, individual traits should be considered when seeking to understand how jobseekers evaluate information to make decisions. A well-known classification of individual differences that has been shown to affect decision-making preference is an individual’s decision-making style: maximisers (those who always try to find the best possible result and carefully evaluate all types of information from different sources) and satisficers (who aim for good-enough results and tend to save time resources). The present study aims to address the gap in the existing literature by exploring the possible reactions of different decision-making styles (maximiser vs. satisficer) in response to recruitment messages with different lengths, valences, forms and provider backgrounds that are provided from various sources. Study 1 and Study 2 are employed as groundwork studies to provide a deeper understanding of maximiser-style and satisficer-style retail-trade jobseekers’ traits. The results illustrate retail trade jobseekers’ job-information-seeking preferences and the relationship between an individual’s maximising tendency and other cognitive-based individual characteristics. The results suggest that employers should not exclude either maximiser-style or satisficer-style jobseekers because the current maximiser-style and satisficer-style employees demonstrated the same levels of job satisfaction with no particular group showed a higher or lower turnover intention. Based on the findings of Study 1 and Study 2, Chapter 5 starts with a scenario-based experiment (Study 3). This experiment assesses whether, when presented with a realistic job-information-searching scenario of receiving basic job information from a typical formal short job advertisement, maximisers and satisficers differ in their need for further information. It also explores whether further evaluation is required from informal information sources in relation to valence and tie strength. Study 3 leads to the reflection that staff ‘word-of-mouth’ (SWOM) messages were influential but could not be controlled by organisations. Study 4 expands the findings of Study 3 and tests whether employers can satisfy more maximiser-style and satisficer-style jobseekers’ information needs to encourage their perceived organisational attractiveness (OA) by providing more detailed formal job advertisement messages. The findings highlight that more details of hard information could effectively satisfy jobseekers’ information needs, even though a group of jobseekers still wanted to search for more experience-based information. However, the findings also show that more detailed messages only slightly increase maximisers’ perceived OA and do not increase satisficers’ perceived OA. By extending the findings of Study 3 and Study 4, three scenario-based experiments (Study 5.1, Study 5.2 and Study 5.3) are designed to test how employers can attract more maximiser-style and satisficer-style jobseekers by tailoring their recruitment messages. The results demonstrate that the SWOM-formed realistic job preview (RJP) messages with some negative information could best increase jobseekers’ perception of source credibility and OA. Furthermore, when maximisers and satisficers looked for different job positions they would perceive the source credibility differently if the background information of the information provider as different. A qualitative-based supplementary study (Study 6) is further conducted to delineate three issues that are not directly measured or not sufficiently clarified in the above-mentioned five studies. This complements Studies 3, 4 and 5 and theoretically enhances the understanding of how jobseekers refer to job recruitment messages and how they evaluate the job information. The results contribute to decision-making theory and social communication theory by demonstrating that the notion of maximisers and satisficers represents a significant and central individual trait in job-application information searching and decision-making in the retail trade. Furthermore, the findings suggest that an individual’s decision-making style is an influential moderator for the effectiveness of communication elements. This research also provides a fundamental basis for further studies to apply individual-differences in human resource management field.

Lightweight Aluminium -Lithium based alloys have high potential for use in aerospace structural components. However, large anisotropy in mechanical properties restricts the use of these alloys. The alloy AA2195 (Al-Li-Cu-Mg-Ag-Zr) is the third generation Al-Li based alloy which is viewed as the most promising choice for structural aerospace applications among the other Al-Li alloys. However, even in this alloy, the combined effect of crystallographic texture and heterogeneous distribution of precipitates leads to mechanical property anisotropy, which is highly undesirable for the formability of this alloy. This underscores the need for developing suitable processing strategies for overcoming the problem of anisotropy. The present thesis aims at exploring the possibilities to improve the mechanical properties and reduce anisotropy in the material by tailoring texture and microstructure in the alloy AA2195 also by designing newer processing schedules and by suitable alloying addition. For this, in the present investigation, texture and microstructure of an already hot rolled plate of AA2195 was modified by employing various types of cross rolling in the processing schedule vis-à-vis an identical processing schedule involving normal unidirectional rolling and the consequent evolution of mechanical properties was examined. The change in strain path led to the formation of weak texture, and a reduction in the degree of anisotropy from 24 % in the as-received hot rolled material to as low as 5 % in the materials processed through routes involving cross rolling. Further, the differently textured sheets were subjected to incremental forming. It was observed that texture weakening by change in the strain path during rolling led to a significant improvement in the formability of the alloy during incremental sheet forming. In the subsequent chapter, further attempts for weakening the texture though a route involving multi-axial forging (MAF) of the cast material were made and consequent evolution of anisotropy in mechanical properties was evaluated. It has been observed that incorporation of multi-axial forging in the processing schedule has led to further weakening of texture. In the next chapter, the effect of severe plastic deformation by Equal Channel Angular Pressing (ECAP) has been examined on the evolution of texture and microstructure and the effect of this process on improvement in mechanical properties has been reported with the detailed explanation of the mechanism. In the next chapter, which aims at suitably modifying the chemistry of the alloy AA2195 by alloying, the effect of scandium (Sc) addition to AA2195 has been studied with special emphasis on the evolution of texture and microstructure during calibre rolling. Addition of Sc has led to enhancement in the degree of grain refinement compared with AA2195 alloy without Sc, when processed using calibre rolling. Finally, it has been concluded that suitable modifications in the processing schedule and the composition modulates the microstructure and texture thereby, improving the mechanical properties

Aluminium alloys, which are the most widely used materials in the aircraft and aerospace industries, find their applications due to high strength–to-density ratio, resistance to catastrophic fracture, high degree of toughness, fabricability including good weldability and availability. High strength aluminum alloys are used in different forms like sheets, forgings and extruded rods, welded and machined components in the aerospace industry. One major application of the aluminium alloys in the space sector is in the launch vehicle and satellite sub-systems. The Indian Space Research Organization has met major challenges of indigenization of suitable aluminium alloys, for example, Al-Cu alloys (like AA2219) and Al–Zn-Mg alloys (like AA7075 and AFNOR 7020). Many failures of the metallic sub-systems made of different grades of aluminum alloys have confirmed that high levels of residual stresses and unacceptable microstructures have played a role. Crystallographic texture in these materials has a very significant role to play in the performance of these materials in service. The anisotropy in the mechanical properties caused by crystallographic texture would add to the woes of the existing problems of residual stresses and directionality in the microstructure. In this context, a detailed study of crystallographic texture and residual stresses of high strength aluminium alloys is mandatory. It is also important to study the influence of texture on the anisotropy in mechanical properties. The present research programme aims at addressing some of these aspects. The entire work has been divided in three major sections, namely macro and micro texture analysis, non-destructive measurement of residual stresses using X-ray Diffraction (XRD) and the Ultrasonic Testing (UST) and the study of anisotropy in the mechanical properties arising due to the above two factors. The thesis composition is as follows. In Chapter I, a detailed survey of the literature has been presented wherein basic physical metallurgy for different aluminum alloys of interest has been given. Thereafter, details of texture measurement by the X-ray diffraction and Electron Back Scatter Diffraction (EBSD) are presented. This is followed by a detailed review on the texture studies carried out in aluminium alloys under various conditions. Literature review on the two non-destructive methods, namely the X-ray diffraction and ultrasonic method has been carried out in detail. In order to account for microstructural changes, Differential Scanning Calorimetry (DSC) was carried out. Recent work on the mechanical property anisotropy arising due to high degree of mechanical working in aluminium alloys has been reviewed. Chapter II includes the experimental details involved in the course of the present investigation. The procedural details of cold rolling and associated microstructural changes are given in this chapter. This is followed by the texture measurement methods. Experimental details of the bulk texture measurement using the X-ray diffraction and micro texture measurements by the Electron Back Scatter Diffraction (EBSD) in the SEM are described. Details of the texture computation procedure as well as micro texture analysis methods are also presented. Basic principles of the non-destructive methods of measuring residual stresses, viz., the X-ray diffraction and the Ultrasonic testing, including the theory of measurements, are dealt with. Finally, the details of measurements of anisotropy in mechanical properties, including simulation carried out, for the three alloys are delineated. Chapter III deals with the results of the crystallographic texture measurements carried out on the cold rolled and artificially aged aluminium alloys. Results obtained from the pole figure analysis, Orientation Distribution Function (ODF) method and estimation of the various fibres present in the cold rolled material and the volume fraction of the texture components are discussed in detail for the three aluminium alloys. Results of the micro texture measurements using the EBSD are presented, explained and analyzed in detail. A comparison of the inverse pole figures (IPFs), Image Quality (IQ) maps, Misorientation angle, Grain Orientation Spread (GOS), Kernal Average Misorientation (KAM), CSL boundaries, Grain size and Grain boundary character distribution (GBCD) for materials cold rolled to different reduction for each of the alloys are done and analyzed. Conclusions are drawn regarding the evolution of texture from the above analysis. Deformation texture components Cu, Bs and S increase from the starting material as the rolling percentage increases. On the other hand, recrystallization texture components of Goss and Cube are observed to be weak. AFNOR 7020 developed the strongest texture followed by the AA7075 and AA2219 alloys. The Bs component is stronger in AFNOR 7020 alloy. This is attributed to the shear banding. Average KAM value increases as the cold working in the material increases confirming that the material contains high dislocation density at higher working percentages. Chapter IV deals with residual stresses in the aluminium alloys. Measurement of residual stresses has been carried out on the same sheets and plates, wherever it was possible, using the two methods. The residual stresses have been measured in two mutually perpendicular directions of the aluminium alloy sheets. Residual stress measurements by the ultrasonic method using the Critically Refracted Longitudinal (LCR) wave technique is also used to measure the subsurface stresses non-destructively. Acousto Elastic Coefficients (AEC) is determined for the alloys, in uniaxial tension. Using the AEC for the alloys, the RS at a depth of 3mm are evaluated using a 2MHz probe. Results of the stresses measured by the two methods have been discussed. The trends and anisotropy in the stress values due to texture are discussed and compared with the literature available. Surface residual stresses by the XRD method show compressive stresses at a majority of the locations. Residual stresses measured by the ultrasonic technique, which has a depth of penetration of about 3mm, have shown tensile stresses on many locations. Residual stresses are influenced by the crystallographic texture. Anisotropy in stress values in the longitudinal and transverse directions is demonstrated. In Chapter V, the anisotropy in mechanical properties for the three alloys is discussed in detail. The anisotropy in the three directions, namely the parallel, transverse and 45 deg orientation to the rolling directions is evaluated. The Lankford parameter, otherwise known as Plastic Anisotropy Ratio “r”, has been measured from the tensile tests of the alloy samples in the cold rolled conditions. These have been compared with the computed “r” from the XRD ODF data using the VPSC simulations and found to be qualitatively matching. These trends are discussed with the available literature on the anisotropy of the mechanical properties for aluminium alloys. Samples subjected to high cold rolling show anisotropy of UTS, YS and ‘n’ values. Experimentally measured “r” values in all the deformation conditions match the trend qualitatively with the simulated ones. The maximum anisotropy was observed at 45o orientation to the rolling direction in all the three alloys. Chapter VI gives the summary of the results from the study and the suggestions for future work.

Aluminium alloys, which are the most widely used materials in the aircraft and aerospace industries, find their applications due to high strength–to-density ratio, resistance to catastrophic fracture, high degree of toughness, fabricability including good weldability and availability. High strength aluminum alloys are used in different forms like sheets, forgings and extruded rods, welded and machined components in the aerospace industry. One major application of the aluminium alloys in the space sector is in the launch vehicle and satellite sub-systems. The Indian Space Research Organization has met major challenges of indigenization of suitable aluminium alloys, for example, Al-Cu alloys (like AA2219) and Al–Zn-Mg alloys (like AA7075 and AFNOR 7020). Many failures of the metallic sub-systems made of different grades of aluminum alloys have confirmed that high levels of residual stresses and unacceptable microstructures have played a role. Crystallographic texture in these materials has a very significant role to play in the performance of these materials in service. The anisotropy in the mechanical properties caused by crystallographic texture would add to the woes of the existing problems of residual stresses and directionality in the microstructure. In this context, a detailed study of crystallographic texture and residual stresses of high strength aluminium alloys is mandatory. It is also important to study the influence of texture on the anisotropy in mechanical properties. The present research programme aims at addressing some of these aspects. The entire work has been divided in three major sections, namely macro and micro texture analysis, non-destructive measurement of residual stresses using X-ray Diffraction (XRD) and the Ultrasonic Testing (UST) and the study of anisotropy in the mechanical properties arising due to the above two factors. The thesis composition is as follows. In Chapter I, a detailed survey of the literature has been presented wherein basic physical metallurgy for different aluminum alloys of interest has been given. Thereafter, details of texture measurement by the X-ray diffraction and Electron Back Scatter Diffraction (EBSD) are presented. This is followed by a detailed review on the texture studies carried out in aluminium alloys under various conditions. Literature review on the two non-destructive methods, namely the X-ray diffraction and ultrasonic method has been carried out in detail. In order to account for microstructural changes, Differential Scanning Calorimetry (DSC) was carried out. Recent work on the mechanical property anisotropy arising due to high degree of mechanical working in aluminium alloys has been reviewed. Chapter II includes the experimental details involved in the course of the present investigation. The procedural details of cold rolling and associated microstructural changes are given in this chapter. This is followed by the texture measurement methods. Experimental details of the bulk texture measurement using the X-ray diffraction and micro texture measurements by the Electron Back Scatter Diffraction (EBSD) in the SEM are described. Details of the texture computation procedure as well as micro texture analysis methods are also presented. Basic principles of the non-destructive methods of measuring residual stresses, viz., the X-ray diffraction and the Ultrasonic testing, including the theory of measurements, are dealt with. Finally, the details of measurements of anisotropy in mechanical properties, including simulation carried out, for the three alloys are delineated. Chapter III deals with the results of the crystallographic texture measurements carried out on the cold rolled and artificially aged aluminium alloys. Results obtained from the pole figure analysis, Orientation Distribution Function (ODF) method and estimation of the various fibres present in the cold rolled material and the volume fraction of the texture components are discussed in detail for the three aluminium alloys. Results of the micro texture measurements using the EBSD are presented, explained and analyzed in detail. A comparison of the inverse pole figures (IPFs), Image Quality (IQ) maps, Misorientation angle, Grain Orientation Spread (GOS), Kernal Average Misorientation (KAM), CSL boundaries, Grain size and Grain boundary character distribution (GBCD) for materials cold rolled to different reduction for each of the alloys are done and analyzed. Conclusions are drawn regarding the evolution of texture from the above analysis. Deformation texture components Cu, Bs and S increase from the starting material as the rolling percentage increases. On the other hand, recrystallization texture components of Goss and Cube are observed to be weak. AFNOR 7020 developed the strongest texture followed by the AA7075 and AA2219 alloys. The Bs component is stronger in AFNOR 7020 alloy. This is attributed to the shear banding. Average KAM value increases as the cold working in the material increases confirming that the material contains high dislocation density at higher working percentages. Chapter IV deals with residual stresses in the aluminium alloys. Measurement of residual stresses has been carried out on the same sheets and plates, wherever it was possible, using the two methods. The residual stresses have been measured in two mutually perpendicular directions of the aluminium alloy sheets. Residual stress measurements by the ultrasonic method using the Critically Refracted Longitudinal (LCR) wave technique is also used to measure the subsurface stresses non-destructively. Acousto Elastic Coefficients (AEC) is determined for the alloys, in uniaxial tension. Using the AEC for the alloys, the RS at a depth of 3mm are evaluated using a 2MHz probe. Results of the stresses measured by the two methods have been discussed. The trends and anisotropy in the stress values due to texture are discussed and compared with the literature available. Surface residual stresses by the XRD method show compressive stresses at a majority of the locations. Residual stresses measured by the ultrasonic technique, which has a depth of penetration of about 3mm, have shown tensile stresses on many locations. Residual stresses are influenced by the crystallographic texture. Anisotropy in stress values in the longitudinal and transverse directions is demonstrated. In Chapter V, the anisotropy in mechanical properties for the three alloys is discussed in detail. The anisotropy in the three directions, namely the parallel, transverse and 45 deg orientation to the rolling directions is evaluated. The Lankford parameter, otherwise known as Plastic Anisotropy Ratio “r”, has been measured from the tensile tests of the alloy samples in the cold rolled conditions. These have been compared with the computed “r” from the XRD ODF data using the VPSC simulations and found to be qualitatively matching. These trends are discussed with the available literature on the anisotropy of the mechanical properties for aluminium alloys. Samples subjected to high cold rolling show anisotropy of UTS, YS and ‘n’ values. Experimentally measured “r” values in all the deformation conditions match the trend qualitatively with the simulated ones. The maximum anisotropy was observed at 45o orientation to the rolling direction in all the three alloys. Chapter VI gives the summary of the results from the study and the suggestions for future work.

Friction stir welding(FSW) is a solid-state metal joining process which is currently being considered for joining of aerospace components. The zones associated with FSW are distinctly different from the fusion weld and their properties also vary. Further, the discontinuities and defects encountered are unique in nature. As most aerospace components are designed with limited margin, the identification of the Friction stir weld defects and discontinuities, and their effect on the performance pose continuous challenges for the quality assessment. Thus, detection, location and characterization of different types of defects encountered in FSW, along with Probability of Detection (POD) of those discontinuities in aerospace friction stir welded components with its varying metallurgical characteristics are the primary objectives of the investigations taken up. The focus has been on capability of different NDE tools in detecting and evaluating different types of defects in FSW joints in the Aluminum alloy AA2219 and to establish the outcome through POD concept.