Dissertations / Theses on the topic 'SDA’s'

Les zéolites sont des matériaux poreux cristallins uniformesformés d'unités TO4 partageant un sommet (T = Si, Al, Ge, etc.). Ils sont préparés sous des conditions hydrothermales, en mélangeant un agent directeur de structure (SDA) approprié avec un gel contenant des composants inorganiques tels que la silice, l'alumine ou le germanium. À un pH et une température spécifiques, le SDA induit la nucléation et la croissance cristalline pour obtenir des zéolites de taille, de forme et de dimension spécifiques. Les zéolites à pores de taille extra-large avec une ouverture de pore supérieure à 0,75 nm suscitent un intérêt croissant de la part des chercheurs en raison de leur activité prometteuse dans le traitement de molécules plus volumineuses, de l'amélioration de la vitesse de diffusion, de la prolongation de la durée de vie du catalyseur et du changement de la sélectivité du produit.Notre objectif est de préparer des SDA avec des substitutions alkyliques différentes en suivant une approche d'expansion de taille, en synthétisant des sels d'ammonium contenant une ou deux entités alcyne. De plus, des sels d'ammonium à base d'imidazole, d'hexaméthylénétanétramine et de composés de 4-phénylpyrridine - ainsi que des voies de synthèse pour la préparation de sels d'ammonium à base de [2.2] paracyclophane en utilisant la réaction de King ont été explorées. En outre, des sels organiques à base de phosphore ont été synthétisés. La préparation, la purification et les premiers résultats de leur utilisation comme SDA dans la synthèse des zéolites seront présentés dans cette thèse
Zeolites are uniformly crystalline porous materials formed of a vertex sharing TO4 units (T= Si, Al, Ge, etc.). They are prepared under hydrothermal conditions, by mixing a suitable structure directing agent (SDA) with a gel containing inorganic components such as silica, alumina or germanium. At specific pH and temperature, the SDA induces nucleation, seed formation and crystal growth to obtain zeolites with specific size, shape and dimension. Extra-large pore size zeolites with pore aperture larger than 0.75 nm aroused increasing interest from researchers due to their promising activity in processing bulkier molecules, improving diffusion rate, prolonging the catalyst lifetime and changing product selectivity. Our goal is to prepare SDA’s having different alkyl substituents following size expansion approach, by synthesizing ammonium salts containing either one or two alkyne moieties. Furthermore, ammonium salts based on imidazole, hexamethyl-enetetramine and 4-phenylpyridine compounds – as well as synthetic paths for the preparation of [2.2] paracyclophane based ammonium salts using King’s reaction were explored. Additionally, organic salts based on phosphorous were synthesized. Preparation, purification and preliminary results of their use as SDAs in zeolite synthesis will be shown in this thesis

In the past few years the demand for light weight compact automotive antennas in the customersdesired mounting position has brought a challenge for the automotive antenna developers. Due to thehigh demands for the accuracy and compactness it became very difficult to develop antenna elementswhich fulfil all the strict requirements. Integrated SDARS (Satellite Digital Audio Radio Service)antenna element is one of such tasks which require strong gain requirements at particular elevationangles for the best reception of the satellite signals along with the car manufacturer’s desired mountingpositions.To achieve the desired objectives for SDARS element, different antenna designs were proposed andtested during the project work. Finally a newly developed two port cylindrical dielectric resonatorantenna (DRA) with a parasitic element is presented due to its high performance, simplicity andcompactness. The newly developed DRA antenna fulfils the strict SiriusXm gain requirements for thechallenging mounting position in the car. The SDARS antenna element is simulated using CSTMicrowave Studio and verified by prototype measurements. The developed DRA antenna element hasa broad beam with a peak gain more than 6dBi at the null position. An axial ratio of less than 3dB isachieved at the peak gain position. Real time 3D far field measurements are taken by using the MiDAS4.1 system which verifies the simulated results of the developed integrated SDARS antenna. A goodagreement is achieved between the simulated and measured results.

Thesis (Ph. D.)--Ohio State University, 2003.
Title from first page of PDF file. Document formatted into pages; contains xvii, 158 p.; also includes graphics Includes bibliographical references (p. 154-158). Available online via OhioLINK's ETD Center

The history of our world is certainly not devoid of disputes and conflicts that have shattered the ability to exercise control over a previously held territory by the state governments all across the globe. Such catastrophic losses for the defeated and grandiose achievements for the victors have defined and described our world for so long with the cost of countless lives of the innocent, yet even today, when sovereignty has undeniably become one of the most frequently used terms in public discourse on international political events, it is surprisingly difficult to ascertain exactly when the sovereignty of the state gets violated or even should be violated.

Effects of pore, secondary dendrite arm spacings (SDAS ), hot isostatic pressing (Hipping), and strontium-modification on fatigue behavior were studied in an aluminum casting alloy (A356.2). Microstructures were revealed by X-ray radiography, light microscopy and scanning electron microscopy. Small-cracks were monitored by taking replicas of the surfaces with which the cracks intersected. As the SDAS increases from 15 to 55 μm, fatigue life decreases by a factor of 3 in low-cycle fatigue, and 100 in high-cycle fatigue. When SDAS is less than 30 mum, the pore size is below a critical size of ∼80 μm and large eutectic constituents initiate cracks; and the initiation life is as high as 70% of the fatigue life. As the SDAS increases beyond 30 μm, pores are the main crack-initiation sites; the initiation life is as low as 5% of the fatigue life. Near-surface oxides initiate the fatigue crack regardless of SDAS. When crack initiated at pore and oxides, fatigue life is well correlated with the size of the initiation site and the effect of SDAS is overshadowed by the effect of pore. Non-hipped A356.2 without Sr shows better fatigue life and the deleterious effect of pores overshadowed the beneficial effect that Sr-modification might have had. Hipping significantly increased the initiation life and small-crack propagation life of A356.2 with Sr as a result of the elimination of the porosity. However, hipping did not significantly improve the fatigue life of A356.2 without Sr. After hipping, Sr-modification is beneficial in improving the crack initiation life, and increasing both small-crack and long-crack propagation lives. Fracture mechanics models (Newman-Raju, and Trantina-Barishpolsky models) yielded similar results on the crack-propagation rate against the effective stress-intensity factor range. In the micro-mechanics model, the theory of continuously distributed dislocations was applied to represent crack and crack-tip plastic zone, and the propagation rate was related to the length of the crack-tip plastic zone. When the grain size is used as the characteristic length of the microstructures, the model predicts the oscillations of the propagation rates and the predicted rates agreed reasonably well with those from experiments.

Ce travail a pour objectif d'étudier la tenue en fatigue de l'alliage de fonderie A356-T6 sous chargement multiaxial. Des essais en fatigue à 106 cycles ont été effectués pour deux rapports de chargements différents à Rσ = 0 et Rσ = -1. La première partie expérimentale est menée sur des éprouvettes issues d'une coulée en ‘V’ avec des défauts naturels de fonderie et des défauts artificiels avec une variation de la microstructure. Suite aux résultats expérimentaux, nous avons montré que la taille des défauts ainsi que la microstructure caractérisée par la SDAS, sont les principaux paramètres qui influencent la limite de fatigue de cet alliage. Par comparaison entre les résultats obtenus à Rσ = 0 et Rσ = -1, il s'avère que la contrainte moyenne joue un rôle primordial sur la sensibilité du matériau à la taille du défaut et à la SDAS. Dans la suite, des modifications ont été menées sur le critère de DSG qui consistent à introduire l’effet de la SDAS au niveau du critère. L’application de ce critère modifié dans un diagramme de Kitagawa pour les différents cas de chargement a montré que l’abattement de la limite de fatigue en fonction de la taille de défaut et de la SDAS est bien décrit. Dans la dernière partie un outil numérique a été développé permettant de simuler la limite de fatigue en partant du procédé de fonderie. Cette démarche est sous forme d’une chaîne de calcul numérique qui permet de simuler la taille de défaut et de la SDAS à partir du procédé de fonderie. Suite à cette simulation, le modèle est capable de prévoir la limite de fatigue en utilisant le critère de DSG modifié. La combinaison entre la loi de Weibull et le critère de DSG permet à la suite de la chaîne de simulation de prévoir ainsi la probabilité de rupture à chaque point de la structure. Nous avons proposé dans cette partie un moule qui permet d’élaborer des éprouvettes avec deux microstructures différentes. Dans cette étude, une deuxième campagne d’essais a été réalisée sur ces éprouvettes afin de valider la simulation numérique sur le moule proposé. Le modèle numérique prévoit raisonnablement bien les résultats expérimentaux obtenus
This study aims to investigate the fatigue behaviour of A356-T6 aluminum alloy. Experimental fatigue tests at 106 cycles have been performed for two loading ratios: Rσ = 0 and Rσ = -1. The first experimental investigation was conducted on specimens from a ‘V’ wedge casting with natural and artificial defects which provides a variation of the microstructure. Following the experimental results, we have shown that defects characterized by their size and the microstructure characterized by SDAS, are the main parameters that control the fatigue limit. By comparing the results obtained for both loading ratios, it appears that the mean stress has an effect on the sensitivity to the defect size effect and microstructure.The DSG criterion was modified to introduce the effect of SDAS. This improved DSG criterion has been employed to predict the Kitagawa diagram for multiaxial loading for different loading cases. The simulation of the modified DSG criterion showed that the reduction of the fatigue limit with the defect size and SDAS is well described. In the last part a numerical model was developed to perform a simulation of the fatigue limit starting from the casting process. Using this numerical model, we simulated the defect size and SDAS depending on the solidification time, eventually the fatigue limit issimulated using the improved DSG criterion. With combining between Weibull law and modified DSG,we predict the probability of failure at each point of the structure. We proposed in this part a mold which let to obtain samples with two different microstructures. In this study, a second fatigue tests was carried out on these samples to validate the numerical simulation on the proposed mold. It turns out that the numerical model provides reasonably well the obtained experimental results

The magnetic Fe–6.5 wt% Si powder was produced by gas atomization and its microstructure was also investigated. The secondary dendritic arm spacing (SDAS) is related to the droplet size, λ = 0.29 · D⁰·⁵, and the numerical solidification model was applied to the system, giving rise to the correlation of microstructure to the solidification process of the droplet. It is found that the solid fraction at the end of recalescence is strongly dependent on the undercooling achieved before nucleation; the chances for the smaller droplets to form the grain-refined microstructures are less than the larger ones. Furthermore, the SDAS is strongly influenced by the cooling rate of post-recalescence solidification, and the relationship can be expressed as follows, λ = 74.2 · (T)⁻⁰·³⁴⁷. Then, the growth of the SDAS is driven by the solute diffusion of the interdendritic liquids, leading to a coarsening phenomenon, shown in a cubic root law of local solidification time, λ = 10.73 · (tf)⁰·²⁹⁶.

In recent years, research on the design and performance evaluation of suboptimal receiver implementations has received considerable attention owing to complexity in the realization of the optimal receiver algorithms over wireless channels. This thesis addresses the effects of using reduced complexity receivers for the Satellite Digital Audio Radio (SDAR), Code Division Multiple Access (CDMA) and UltraWideband (UWB) communications technologies. A graphical-user-interface simulation tool has been developed to predict the link reliability performance of the SDAR services in the continental United States. Feasibility study of receiving both satellite and terrestrial repeater signals using a selection diversity (single antenna) receiver has also been performed. The thesis also develops a general mathematical framework for studying the efficacy of a sub-optimal generalized selection combining (GSC) diversity receiver over generalized fading channel models. The GSC receiver adaptively combines a subset of M diversity paths with the highest instantaneous signal-to-noise ratios (SNR) out of the total L available diversity paths. The analytical framework is applicable for rake receiver designs in CDMA and UWB communications.
Master of Science

Aluminum alloys are widely used in many manufacturing areas due to good castability, lightness and mechanical properties. The purpose of this research is to investigate copper’s influence on an Al-Si-Mg alloy (A356). Copper in the range of 0.6 – 1.6 wt. % has been used in an A356 aluminum based alloy. In this work a simulation of three different casting processes, sand-, die- and high pressure die-casting has been employed with the help of gradient solidification equipment. The microstructure of the samples has been studied by optical and scanning electron microscopy. Materials in both as-cast and heat treated states have been investigated through tensile test bars  to get the mechanical properties of the different conditions.

 

Questions that have been subjected to answer are what influence does copper have on the plastic deformation and on fracture behavior and whether there is a relationship between the content of copper and increased porosity or not; and in that case explore this relationship  between the amount of copper and the mechanical behaviour.

 

It has been analyzed that a peak of mechanical properties is obtained with a content about 1.6 wt. % copper. The increment of copper seems to have a remarkable impact on the mechanical properties and especially after the aging process showing a large raise on the ultimate tensile strength and yield strength.

Relationship between the copper content and increased porosity could not be found.

Aujourd'hui, les nouveaux appareils électroniques de télécommunications tendent toujours à plus d'innovations, plus de services et le tout dans de faibles dimensions. Face à un nombre de standards toujours croissant, les nouvelles antennes associées doivent être capables de couvrir plusieurs bandes de fréquences avec des caractéristiques de rayonnement variées, en un minimum d'encombrement. Cette thèse a permis la conception de plusieurs antennes combinées à polarisations multiples pour les applications spatiales. À partir d'un état de l'art d'antennes de géométries variées et devant la complexité de disposer de plusieurs types de polarisations au sein d'un même élément, l'étude a été divisée en deux parties. La première présente en particulier une antenne quadribande fonctionnant en polarisation linéaire pour les standards Bluetooth et WLAN. Sa géométrie consiste en un élément de fine épaisseur, replié en forme de U, entouré d'une cavité cylindrique. La seconde partie propose plusieurs antennes bibandes en polarisation circulaire, basées sur le principe d'éléments imprimés carrés à coins coupés: une antenne monocouche pour les standards GPS-SDARS et une antenne bicouche dédiée aux deux bandes de fréquences GPS existantes. Au final, en combinant ces différents éléments rayonnants, on obtient des antennes multistandards regroupant les deux types de polarisations, linéaire et circulaire.

Abstract

The purpose of this research is to investigate the influence of Manganese (Mn) on cast aluminum alloys where a substantial amount of Iron (Fe) is included. Ductility and tensile strength need to be improved in recycled aluminum alloys where greater amounts of Fe are found. Fe is a common impurity and is known to be detrimental to mechanical properties and in order to neutralize the effects of Fe; modifiers such as Mn are added. In this investigation, attempts will be carried out aiming to find the optimal amount of Mn. Other related topics that will be discussed are whether there exists a Mn/Fe ratio which clearly modifies the harmful iron- rich phases and improves the properties for a certain alloy or not. Also, will the heat treatment have a significant effect on mechanical properties? These are some of the questions that will be answered in this paper.

It is hard to find research articles that focus only on the influence of Mn on the microstructure and mechanical properties of Al-Si cast alloys. Much of the work that is already published concerns only a specific alloy and casting method. In this work three different casting processes, sand-, die- and high pressure die-casting, will be simulated by using gradient solidification equipment. Furthermore, the influence of heat treatment on the mechanical properties will be examined.

The results showed that the solidification rate had the biggest impact on the microstructure and mechanical properties of the alloys, where the fastest cooling rate gave the best results. The effect of Mn seems to influence the samples with coarser microstructures significantly where it had time to modify the Iron-rich needles, also called the β-phase. At higher cooling rates the impact of Mn was impeded. It has been observed that a high content of Mn (around 0.6%) needs to be added before the properties start to improve. UTS (Ultimate Tensile Strength) and YS (Yield Strength) are improved while ductility is lowered. Heat treatment did not seem to have any influence on the effects of Mn.

L'alluminio e le sue leghe sono fra i materiali più importanti nell’ambito dell'ingegneria meccanica e trovano spazio in tutti i principali settori dell’industria aerospaziale e motoristica. La loro versatilità è legata principalmente all’elevata resistenza specifica indotta dal trattamento termico, all’ottima resistenza alla corrosione e all’elevata conducibilità elettrica e termica. Purtroppo l’effetto di rinforzo indotto del trattamento termico viene ad essere compromesso nel caso di applicazioni delle leghe a temperature superiori ai 200°C. Negli ultimi anni, al fine di aumentare l’efficienza e la potenza dei motori endotermici, le temperature a cui questi sono sottoposti si sono innalzate. Per tale ragione si stanno sviluppando e studiando leghe che, attraverso l’aggiunta di opportuni elementi, possano mantenere alte proprietà meccaniche anche a temperature superiori ai 200°C. L’obiettivo della presente ricerca è valutare l’influenza della microstruttura sulle proprietà meccaniche in temperatura di due leghe di alluminio per applicazioni in fonderia, C355 e A354, aventi come elementi principali di lega Si, Cu e Mg.

The presented diploma thesis deals with various types of quenching and their respective effects on mechanical and structural properties of AlSi7Mg0.6 alloy castings. Cast with precision casting technology into a self-supporting ceramic shell made by plaster investment technology, flat test bars cast by Alucast were used as experimental samples. Sample castings were used in both cast state and after T6 heat treatment. Air-flow and air-water combination with varying water passage (spraying) were used as the quenching media in the quenching process of the castings. In order to evaluate the effect of five different quenching processes on the structure and mechanical properties of the castings, the method of light microscopy, Brinell hardness test and static traction test were used. Evaluation and porosity and SDAS quantifications were carried out by means of image analysis. Experiments did not prove right the hypothesis holding that low SDAS values inevitably mean higher mechanical properties of the castings. On the other hand, distinct is the negative influence of heterogeneous structure and porosity. Despite the fact that the heat treatment was successful in reducing the influence of structural inhomogeneities, it cannot be concluded that spray quenching has an utterly positive bearing on the mechanical and structural properties of the castings.

This thesis work deals with the volume changes during the solidification of cast irons and peritectic steels. The volume changes in casting metals are related to the expansion and/or contraction of the molten metal during solidification. Often, different types of shrinkage, namely macro- and micro-shrinkage, affect the casting quality. In addition to that, exposure of the metal casting to higher contraction or expansion during the solidification might also be related to internal strain development in samples, which eventually leads to surface crack propagation in some types of steel alloys during continuous casting. In consequence, a deep understanding of the mechanisms and control of the solidification will improve casting quality and production. All of the experiments during the entire work were carried out on laboratory scale samples. Displacement changes during solidification were measured with the help of a Linear Variable Displacement Transformer (LVDT). All of the LVDT experiments were performed on samples inside a sand mould. Simultaneously, the cooling curves of the respective samples during solidification were recorded with a thermocouple. By combining the displacement and cooling curves, the volume changes was evaluated and later used to explain the influence of inoculants, carbon and cooling rates on volume shrinkages of the casting. Hypoeutectic grey cast iron (GCI) and nodular cast iron (NCI) with hypo-, hyper- and eutectic carbon compositions were considered in the experiments from cast iron group. High nickel alloy steel (Sandvik Sanbar 64) was also used from peritectic steel type. These materials were melted inside an induction furnace and treated with different types of inoculants before and during pouring in order to modify the composition. Samples that were taken from the LVDT experiments were investigated using a number of different  methods in order to support the observations from the displacement measurements:  Differential Thermal Analysis (DTA), to evaluate the different phase present; Dilatometry, to see the effect of cooling rates on contraction for the various types of alloys; metallographic studies with optical microscopy; Backscattered electrons (BSE) analysis on SEM S-3700N, to investigate the different types of oxide and sulphide nuclei; and bulk density measurements  by applying Archimedes' principle. Furthermore, the experimental volume expansion during solidification was compared with the theoretically calculated values for GCI and NCI. It was found that the casting shows hardly any shrinkage during early solidification in GCI, but in the eutectic region the casting expands until the end of solidification. The measured and the calculated volume changes are close to one another, but the former shows more expansion. The addition of MBZCAS (Si, Ca, Zr, Ba, Mn and Al) promotes more flake graphite, and ASSC (Si, Ca, Sr and Al) does not increase the number of eutectic cells by much. In addition to that, it lowers the primary austenite fraction, promotes more eutectic growth and decreases undercooled graphite and secondary dendritic arm spacing (SDAS). As a result, the volume expansion changes in the eutectic region. The expansion during the eutectic growth increase with an increase in the inoculant weight percentage. At the same time, the eutectic cells become smaller and increase in number. The effect of the inoculant and the superheat temperature shows a variation in the degree of expansion/contraction and the cooling rates for the experiments. Effective inoculation tends to homogenize the eutectic structure, reducing the undercooled and interdendritic graphite throughout the structure. In NCI experiments, it was found that the samples showed no expansion in the transversal direction due to higher micro-shrinkages in the centre, whereas in the longitudinal direction the samples shows expansion until solidification was complete.   The theoretical and measured volume changes agreed with each other. The austenite fraction and number of micro-shrinkage pores decreased with increase in carbon content. The nodule count and distribution changes with carbon content. The thermal contraction of NCI is not influenced by the variation in carbon content at lower cooling rates. The structural analysis and solidification simulation results for NCI show that the nodule size and count distribution along the cross-sections at various locations are different due to the variation in cooling rates and carbon concentration. Finer nodule graphite appears in the thinner sections and close to the mold walls. A coarser structure is distributed mostly in the last solidified location. The simulation result indicates that finer nodules are associated with higher cooling rate and a lower degree of microsegregation, whereas the coarser nodules are related to lower cooling rate and a higher degree of microsegregation. As a result, this structural variation influences the micro-shrinkage in different parts. The displacement change measurements show that the peritectic steel expands and/or contracts during the solidification. The primary austenite precipitation during the solidification in the metastable region is accompanied by gradual expansion on the casting sides. Primary δ-ferrite precipitation under stable phase diagram is complemented by a severe contraction during solidification. The microstructural analysis reveals that the only difference between the samples is grain refinement with Ti addition. Moreover, the severe contraction in solidification region might be the source for the crack formation due to strain development, and further theoretical analysis is required in the future to verify this observation.

QC 20170228

The influence of processing and process parameters plays a key role for the Aluminium foundry and transport industries as it affects the quality and soundness of the cast products. Particularly, the choice of a process chain in Aluminium foundry, otherwise of process parameters, influences the reject rates, hence casting costs, the process yield and the production rate. The process chain in Aluminium foundry is a complex sequence of processes and the final casting quality depends on many parameters. Several aspects of this subject are still not fully understood. The motivation of the research presented in this doctoral thesis work was, therefore, to fill this gap in knowledge. The study has aimed at understanding the influence of various process and process parameters of foundry on the quality of aluminium alloy castings and, in particular, Al-Si based castings. A literature review and a sufficient background of previously reported results on the influence of processing and process parameters on the quality of aluminium alloy castings, physical fundamentals as well as industrial challenges, motivation and goals were carried out. Special attention in Aluminium process chain has been given to: The modification of aluminium-silicon cast alloys: before casting aluminium alloys, the molten metal can be treated in order to improve the microstructure and properties of alloys by addition of small quantities of certain "modifying" elements. The pouring of molten metal into the mould: this is one of the critical steps in foundry technology, since the behaviour of the liquid and its subsequent solidification and cooling determine whether the cast shape will be properly formed, internally sound and free from defects. The chill casting processes, such as gravity, low-pressure and high-pressure die casting processes: the essential feature of chill casting is the use of permanent metal moulds, into which the molten alloy is either poured directly or injected under pressure, giving rise to the separate processes of gravity and low/high pressure die casting. Permanent moulds offer obvious advantages in terms of simplicity of production for large quantities of parts, but are subject to limitations yet to be discussed. The heat treating process applied to high-pressure die castings: conventional die castings are utilised to produce many products but unfortunately the presence of porosity limits the application. In addition to porosity, the microstructure inherent with conventional die casting could not meet the mechanical requirements needed for many applications. Subsequent heat treating, which can positively alter the microstructure, is rarely possible due to defects that emerge during thermal processing, such as blistering.

This thesis presents RF front-end system design for both WLAN (Wireless Local Area Network) and SDARS (Satellite Digital Audio Radio System) applications using adaptive smart antenna technique. It is important to understand that smart antenna system with adaptive beam-forming provides the following advantages: 1. It can concentrate radio transmission on specific directions by modifying transmit/receive phase and amplitude characteristics, and therefore provides greater coverage and increased capacity. 2. It can greatly reduce multi-path fading effect and co-channel interference. This thesis first presents a complete 4-element smart antenna system for IEEE 802.11b/g WLAN applications. The prototype presented can interconnect with an of-the-shelf WLAN network card. The system is controlled via a microcontroller that adjusts the array pattern to capture the best signal. Measurements show that the system can increase the RSSI (Received Signal Strength Indicator) level significantly and therefore the SNR (Signal to Noise Ratio). This prototype is the first step towards a novel DBF (Digital Beam-Forming) smart antenna architecture. The second part of the thesis presents a 2-element smart antenna system for SDARS application. This prototype can be connected with an of-the-shelf SDARS digital receiver. The system was tested in a chamber and measurements show a controlled beam and increased gain. Ansoft HFSS was used to simulate the 2-element smart antenna and validate the testing results.

Within industrial product development processes there is an increasing demand towards reliable predictions of the material behavior, which aims to promote a property driven development that can reduce the lead times. The implementation of simulation based product development with integrated casting simulation may enable the design engineers to gain an early understanding of the products with relation to castability, and orient the subsequent design refinement so as to achieve the desired mechanical properties. This work investigates the suitability of three commercial casting simulation softwares –MAGMA 5.2, NovaFlow & Solid 4.7.5 (NFS) and Click2Cast 3.0 (C2C)–, with respect to the needs of design engineers, such as prediction of shrinkage porosity and mechanical properties with relation to the design. Simplified solidification simulations suitable for this stage were thus performed for three high pressure die cast components with different geometrical constraints. The comparability between the solidification and cooling behaviour predicted by the three softwares was studied, and showed that a reasonably good agreement between predicted solidification times by MAGMA and NFS could be obtained, albeit not between predictions by MAGMA and C2C. Predictions by the three softwares of the hot spot/porosity areas showed to have a good agreement. The calculation times by each software were compared, and MAGMA was seen to have the best performance, yielding significantly shorter times than NFS and C2C. The results obtained were also compared to experimental investigations of porosity, microstructural coarseness, and mechanical properties. There was a good agreement between the predicted hot spot areas –i.e. areas in the geometry that solidify last– and the findings of porosities in the actual castings, meaning that solidification simulations might be able to provide important information for the prediction of most of shrinkage related porosity locations that are related to the casting geometry. However, the lack of a detailed knowledge at the design stage of the casting process limits the possibilities to predict all porosities. The predicted microstructure and mechanical properties by MAGMA non-ferrous were seen to have a good agreement in trend with the experimental data, albeit the predicted values showed large differences in magnitude with the experimental data. Although, the MAGMA non-ferrous module was not developed for HPDC components, it was interesting to study if it could be applied in this context. However, the models seem to need adoption to the HPDC process and alloys. In conclusion, with a limited knowledge of the manufacturing parameters, simplified solidification simulations may still be able to provide reasonably reliable and useful information during early development stages in order to optimise the design of castings.

Digital image correlation techniques (DICT), a non-contact deformation measuring technique based on gray value digital images, have become increasingly used over the last years. By using the DIC technique during a tensile test, the deformation behavior of different engineering material under an applied load can be determined and analyzed. Digital images, acquired from a tensile test, can be correlated by using DICT software and from that the local or global mechanical properties can be calculated. The local or global mechanical properties determination of a flat test specimens are based on the displacements or changes in a previous stochastic sprayed or natural pattern. The used material for this purpose is cast silicon (Si) based aluminium (Al) component, designated as AlSi7Mg0.3 (Anticorodal-78 dv). The hypoeutectic Al- Si alloy is widely applicable for engine constructions, vehicle and aerospace constructions, shipbuilding, electrical engineering and constructions for food industry. There are many microstructural parameters in a binary system Al- Si alloys, which the mechanical properties can be depended on, for instance phase distribution, Secondary Dendrite Arm Spacing (SDAS), morphology of Si particles (Roundness) and microscopic defects or pores. All these parameters can contribute to enhance the proper mechanical performance (e.g. Strength and ductility) in the Al-Si cast components.

Additive manufacturing can bring several advantages in tooling applications especially hot working tooling as high pressure die casting. Printing of conformal cooling channels can lead to improved cooling and faster solidification, which, in turn, can possibly result in better quality of the cast part. However, few studies on advantages of additive manufactured tools in high pressure die casting are published.The aim of this study was to investigate and quantify the effect of conformal cooling on microstructure and mechanical properties of high pressure die cast aluminum alloy. Two tools each consisting of two die inserts were produced with and without conformal channels using additive manufacturing. Both tools were used in die casting of aluminum alloy. Aluminum specimens were then characterized microstructurally in light optical microscope for secondary arm spacing measurements and subjected to tensile and hardness testing. Cooling behavior of different inserts was studied with a thermal camera and by monitoring the temperature change of cooling oil during casting. Surface roughness of die inserts was measured with profilometer before and after casting.Thermal imaging of temperature as a function of time and temperature change of oil during casting cycle indicated that conformal insert had faster cooling and lower temperature compared to conventional insert. However, thermal imaging of temperature after each shot in a certain point of time showed higher maximum and minimum temperature on conformal die surface but no significant difference in normalized temperature gradient compared to the conventional insert.The average secondary dendrite arm spacing values were fairly similar for samples from conventional and conformal inserts, while more specimens from conventional insert demonstrated coarser structure. Slower cooling in conventional insert could result in the coarser secondary dendrite arm spacing.Tensile strength and hardness testing revealed no significant difference in mechanical properties of the specimens cast in conventional and conformal die inserts. However, reduced deviations in hardness was observed for samples cast with conformal insert. This is in agreement with secondary dendrite arm spacing measurements indicating improved cooling with conformal insert.Surface roughness measurement showed small wear of the inserts. More castings are needed to observe a possible difference in wear between the conventional and conformal inserts.Small observed differences in cooling rate and secondary arm spacing did not result in evident difference in mechanical properties of the aluminum alloy but the variation in properties were reduced for samples cast with conformal cooling. Future work may include more accurate measurement of cooling behavior with a thermocouple printed into the die insert, casting of thicker specimen for porosity evaluation and fatigue testing and longer casting series to evaluate the influence of conformal cooling on tool wear.

A área da Conservação em Biologia tem como principais objetivos cuidar e encontrar meios de supervisão constante dos componentes dos ecossistemas. A eterna vigilância exige ao biólogo um olhar cada vez mais abrangente e interdisciplinar, não só dos processos específicos que ocorrem no mundo natural, mas também da procura de respostas para a gestão (dentro daquilo que é possível) desse mesmo mundo natural. O presente estudo focou-se em pesquisar um conjunto de indicadores informativos sobre o status dos serviços dos ecossistemas e de elementos da diversidade biológica de uma área no norte de Moçambique, que compreendeu a “Messalo Wilderness Area” e as praias da Ilha de Vamizi. Aplicou-se, assim uma metodologia “bottom-up”, em que o exercício de diagnóstico implicou o envolvimento dos “stakeholders” locais, e.g. na auscultação de carências, benefícios vivenciados, e de soluções para conflitos com a vida selvagem. O diagnóstico confirmou uma área de riqueza biológica considerável, pressionada pelo número crescente de habitantes no local, e de habitantes temporários oriundos, por exemplo, da Tanzânia. Como resposta à necessidade de gerir os recursos locais de forma mais eficaz, com vista à sua preservação mas também ao alívio da pobreza local, foi elaborado um plano de gestão para a “Messalo Wilderness Area”. Conta-se entre as espécies emblemáticas ameaçadas na região, as tartarugas marinhas, Chelonia mydas e Eretmochelys imbricata, assim como os seus habitats de nidificação; e o elefante africano, Loxodonta africana, que compete com o Homem diretamente por recursos naturais (água em períodos de estação seca, e alimentos com invasão e destruição de propriedade /campos de cultivo). Como contributos para conservação da espécie emblemática em terra e por ser um problema grave identificado pelos locais desenvolveu-se e testou-se uma solução tecnológica de sinalização de elefantes. Os sensores mostraram resultados positivos para os objetivos estipulados: uma solução mais barata e não invasiva para a mitigação do conflito Homem-elefante. Como contributos para conservação das espécies emblemáticas na costa, nos seus habitats de nidificação, realizou-se um estudo da biologia reprodutiva das tartarugas marinhas nidificantes na ilha de Vamizi, tendo-se gerado os indicadores de nidificação para esta região de Moçambique, e que permitiram comparações com outras regiões do Índico e do Globo. Das análises efetuadas chegou-se à conclusão que seria fundamental melhorar a monitorização das tartarugas marinhas, tendo-se desenvolvido uma aplicação tecnológica para o campo, o “software Turtles”, que foi testada num estudo piloto com sucesso. Trata-se de um contributo com implicações a nível global, e que altera a metodologia de campo. Os dados recolhidos e analisados de Vamizi pré software mostram taxas de eclosão e de emergência de juvenis elevados (acima dos 80% para as green e para as hawksbill), conferindo à ilha um destaque/estatuto de boa incubadora de tartarugas marinhas. A análise de ADN mitocondrial revelou, também, um considerável número de haplótipos para a região (11 para as green e 14 para as hawksbill), pelo que o estudo aprofundado de outras amostras de outros habitats próximos (de nidificação e de desenvolvimento) revelarão interconectividades e padrões de dispersão geográfica com relevância para a definição de uma “Regional Management Unit” mais sólida. Os resultados demonstram a necessidade de alargar as medidas de conservação das tartarugas marinhas na região, com intensificação dos programas de monitorização nas praias nidificantes, de monitorização da atividade dos pescadores nos habitats de desenvolvimento dos juvenis, e na colheita de amostras para análises moleculares e cruzamento dessa informação com dados de outras partes do Índico Oeste. Dado que a redistribuição de espécies marinhas em consequência da interferência das atividades antropogénicas com os ciclos biogeoquímicos, é uma constatação anunciada por estudos científicos, criar uma “consciência ecológica”, ou uma cultura do “cuidar” torna-se uma meta a atingir em termos globais. Assim, o desenho de um plano curricular para o ensino das Ciências, que colmatem essa necessidade de uma forma inequívoca é, também apresentado à comunidade, como base para debate.
Conservation biology has the main objective of caring and finding strategies for constant supervision of ecosystems components. This eternal vigilance mode demands an interdisciplinary and wider vision from biologists, not only concerning specific processes of the natural world, but also in searching for management answers (in what is possible) for that same natural world. This study focused in searching a group of indicators about ecosystems services status and about biological diversity elements from an area in the North of Mozambique, which comprised the “Messalo Wilderness Area” and the beaches of Vamizi Island. A “bottom-up” approach was applied, using a diagnose exercise involving local stakeholders, e.g., in documenting experienced needs and benefits, and inquiring for solutions to solve the human-wildlife conflicts. The results confirmed an area with considerable biological richness, pressured by the crescent number of local inhabitants, and of foreign people from, for example, Tanzania. As a response to the need of managing effectively local resources, aiming at preserving, but also alleviating local poverty, a management plan was designed for the “Messalo Wilderness Area”. As emblematic species at risk in the area we list the marine turtles, Chelonia mydas and Eretmochelys imbricata, as well as their nesting habitats; and the African elephant, Loxodonta africana, which competes directly with man for natural resources (water in dry season periods, and food with invasion and destruction of crops and property). As contributions for the conservation of emblematic species on land, and because it is a grave problem identified by local people, a technological solution to signal elephants was developed and tested. The sensors showed positive results for the stipulated objectives: an affordable and non-invasive solution to mitigate the human-elephant conflict. As contributions for the conservation of emblematic species on the coast, at the nesting habitats, a reproductive biology study of the nesting marine turtles from the Vamizi Island was carried, that generated nesting indicators for that Mozambican region, and that enabled comparing it with other Indian Ocean and Globe regions. The analysis concluded that the monitoring program needs to be improved, hence the development of a field technological application, the “Turtles” software, which was tested with success in a pilot study. This is a contribution with global implications, that changes field methodology. The data collected in Vamizi and analysed before the software development, showed high hatching and emergency successes (above 80% for the green turtles and for the hawksbill turtles), conferring to the Island the status of good incubation spot for marine turtle’s eggs. The mitochondrial DNA analysis revealed, also, a considerable number of haplotypes for the region (11 for the green’s, and 14 for the hawksbill’s), hence an in-depth study of more samples from nearby habitats (nesting and development) will reveal relevant interconnectivities and geographic dispersal patterns for the definition of a more solid Regional Management unit. The results show the need for extend the conservation strategies for the marine turtle’s conservation in the region, with the intensification of the nesting beach monitoring programs, of the fisherman practices monitoring in the development habitats, and in collecting samples for molecular analysis to crosscheck information with other nesting/foraging/development spots in the Indian Ocean. Because it is an announced scientific evidence that a redistribution of marine species is occurring due to the interference of Man on the biogeochemical cycles, to build up an “ecological conscience”, or a “caring culture” is a goal to achieve globally. Hence, the design of a curriculum to teach Science to fulfil this need in an unambiguous way, is also shown to the scientific community, to start a debate.
Programa Doutoral em Biologia