Joining copper to stainless steel by friction stir diffusion process

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para obtenção do Grau de Mestre em Engenharia MecânicaOne of the major trends in welding and joining technology is to join dissimilar materials taking advantage of individual materials properties. Among these, copper to stainless steel joining has significant industrial applications and importance where e.g. the highest electrical and thermal conductivities are required to engineering materials associated to good corrosion resistance. However, joining these materials is difficult due to their very different chemical composition and thermo-physical properties. Additionally, they easily form intermetallic phases that deteriorate the mechanical strength of the joint. Thus investigating the feasibility of applying alternative processing technologies is relevant. Solid state processes have been investigated for this application, namely friction stir welding. Recently, a variant has been exploited where local diffusion is the fundamental joining mechanism triggered by friction stir. The advantage of friction stir diffusion process is the minimal detrimental effect on both materials, preventing some critical identified problems. Since this process is not well developed, this thesis aimed to study friction stir diffusion process (FSDP) to join copper to stainless steel. Lap joints were produced varying processing parameters, namely, rotation and travel speeds and axial forging force. The effect of processing parameters on the width of effective joining was studied, as well the joints characterization for mechanical resistance properties and microstructural features at the interface. The thermo-mechanical conditions and time during the FSDP resulted in an interface with diffusion between both materials below 3 μm. The shear strength of the lap joints depends on the material thickness involved, but joining efficiencies up to 73.8 % were achieved

Miller cycle analysis using EGM

The Entropy Generation Minimization (EGM) method is based on the analysis by three sciences (thermodynamics, fluid flow and heat transfer) of the different processes that may occur in a system or in an equipment. Herein the EGM method is applied to internal combustion engines to determine the entropy generation caused by different processes. A model incorporating entropy generation calculations is used to assess various engines configurations. Otto cycle was tested and Variable Valve Timing (VVT) and Variable Compression Ratio (VCR) were applied so thermodynamic benefits could be tested and evaluated. With the referred model, the Miller cycle variables are analyzed in order to establish the best working conditions of an engine under a certain load. The intake and exhaust valve timing, combustion start, compression ratio adjustment and heat transfer are the variables for which a best working condition is determined based on the minimization of the entropy generation of the several engine processes.Fundação para a Ciência e a Tecnologia (FCT)Fundo Social Europeu (FSE

Direct comparasion of an engine working under Otto, Miller end Diesel cycles : thermodynamic analysis and real engine performance

One of the ways to improve thermodynamic efficiency of Spark Ignition engines is by the optimisation of valve timing and lift and compression ratio. The throttleless engine and the Miller cycle engine are proven concepts for efficiency improvements of such engines. This paper reports on an engine with variable valve timing (VVT) and variable compression ratio (VCR) in order to fulfill such an enhancement of efficiency. Engine load is controlled by the valve opening period (enabling throttleless operation and Miller cycle), while the variable compression ratio keeps the efficiency high throughout all speed and load conditions. A computer model is used to simulate such an engine and evaluate its improvement potential, while a single cylinder engine demonstrates these results. The same base engine was run on the test bench under the Diesel cycle, Otto cycle and Miller cycle conditions, enabling direct thermodynamic comparisons under a wide variety of conditions of speed and load. The results show a significant improvement of the Miller cycle over the Otto cycle engine. Comparisons of the Miller engine with the Diesel engine shown that it is possible to have a SI engine with better efficiency than a similar Diesel engine for most of the working conditions.Fundação para a Ciência e a Tecnologia (FCT) e Fundo Social Europeu (FSE) - SFRH/BD/11194/2002, FCT/FEDER POCI/ENR/59168/2004, POCI/EME/59186/200

Desenvolvimento do conceito de motor sobre-expandido : análise teórica, numérica e experimental

Os motores de combustão interna de ciclo Diesel têm, convencionalmente, maior rendimento que os motores de ignição comandada. Porém, é possível, com recurso a técnicas de variação de abertura de válvulas e de variação de taxa de compressão, aumentar o rendimento de motores de ignição comandada para valores superiores aos dos motores Diesel. Este trabalho relata o potencial de alteração do vulgar ciclo Otto para outros ciclos de ignição comandada com elevado rendimento, mesmo superior ao do ciclo Diesel. Esta demonstração é feita de 3 modos: pelo recurso à termodinâmica base; usando modelação de funcionamento de motores; e por testes laboratoriais, usando um motor Diesel que é convertido em ciclo Otto, ao qual se varia a duração de abertura da válvula de admissão e o valor da taxa de compressão. Prova-se, em todos os 3 modos (teórico, numérico e experimental), que o motor de ignição comandada de ciclo sobre-expandido com variação da taxa de compressão é o que proporciona maior rendimento.Fundação para a Ciência e a Tecnologia (FCT) - POCI/ENR/59168/2004, POCI/EME/59186/2004

The building activities in ‘Bracara Augusta’. The building process of a city: the agents and the craftsmen

Os construtores e artesãos de Bracara Augusta assumiram um papel importante na economia da cidade. Formam um grupo de indivíduos complexo e diversificado, frequentemente invisíveis nas fontes escritas, cuja atividade recuperamos através da Arqueologia. A cidade conheceu, desde muito cedo, e ao longo da sua história, um protagonismo crescente, caracterizado por importantes funções administrativas e religiosas. Este crescimento político gradual foi acompanhado de uma significativa e permanente actividade construtiva, cuja análise nos transporta ao universo da economia, do mundo social do trabalho, da inovação e das modas. Neste artigo, procuraremos identificar os vários ofícios que estão por de trás desse dinamismo, frequentemente denunciados pelas estruturas e materiais que produziram, apreciaram e/ou adquiriram.Les constructeurs et les artisans de Bracara Augusta ont joué un rôle prépondérant dans l´économie de la ville. Il s´agit d´un groupe d´individus complexe et diversifié, dont les documents écrits parlent peu ou très peu, passible d´être discerné par l´archéologie. La ville a connu, très tôt, et tout au long de son histoire, une dimension croissante, signalée par d´importantes fonctions administratives et religieuses. Ce développement politique graduel a été accompagné d´une activité constructive notoire et permanente, dont l´analyse nous mène vers l´univers de l´économie, du monde social du travail, de l´innovation et des modes. Nous essaierons, dans cette réflexion, d´esquisser les différentes figures qui se cachent derrière ce dynamisme, cela à partir des traces qu´elles ont laissées sur les structures et matériaux qu´elles ont produits, appréciés et/ou acquis

Diagnostic evaluation of chronic venous insufficiency cases using thermal imaging

The use of infrared thermography in surgery of Varicose Veins on the inferior limbs is presented. The study was executed at Polytechnic Institute of Bragança and at the Regional Hospital of Bragança, Portugal. The most suitable steps to measure with this technology were determined prior to the clinical studies, where a minimum waiting time of 10 minutes was determined for each individual to reach thermal equilibrium. Both inferior limbs were compared for each patient and it was found that in 75% of the cases there was an aggravation of the healthier leg. In one of the cases residual veins appear. It was concluded that regular thermographic exams on post-operatory allow a closer follow up of the recovery of the operated limb, as well as the evolution of the non-operated limb

Diagnostic evaluation of chronic venous insufficiency cases using thermal imaging

The use of infrared thermography in surgery of Varicose Veins on the inferior limbs is presented. The study was executed at Polytechnic Institute of Bragança and at the Regional Hospital of Bragança, Portugal. The most suitable steps to measure with this technology were determined prior to the clinical studies, where a minimum waiting time of 10 minutes was determined for each individual to reach thermal equilibrium. Both inferior limbs were compared for each patient and it was found that in 75% of the cases there was an aggravation of the healthier leg. In one of the cases residual veins appear. It was concluded that regular thermographic exams on post-operatory allow a closer follow up of the recovery of the operated limb, as well as the evolution of the non-operated limb

Generation of entropy in spark ignition engines

Recent engine development has focused mainly on the improvement of engine efficiency and output emissions. The improvements in efficiency are being made by friction reduction, combustion improvement and thermodynamic cycle modification. New technologies such as Variable Valve Timing (VVT) or Variable Compression Ratio (VCR) are important for the latter. To assess the improvement capability of engine modifications, thermodynamic analysis of indicated cycles of the engines is made using the first and second laws of thermodynamics. The Entropy Generation Minimization (EGM) method proposes the identification of entropy generation sources and the reduction of the entropy generated by those sources as a method to improve the thermodynamic performance of heat engines and other devices. A computer model created and implemented in MATLAB Simulink was used to simulate the conventional Otto cycle and the various processes (combustion, free expansion during exhaust, heat transfer and fluid flow through valves and throttle) were evaluated in terms of the amount of the entropy generated. An Otto cycle, a Miller cycle (over-expanded cycle) and a Miller cycle with compression ratio adjustment are studied using the referred model in order to evaluate the amount of entropy generated in each cycle. All cycles are compared in terms of work produced per cycle.Fundação para a Ciência e a Tecnologia (FCT) - FCT/FEDER POCI/ENR/59168/2004Fundo Social Europeu (FSE