• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 61
  • 7
  • 6
  • 5
  • 5
  • 4
  • 3
  • 2
  • 2
  • 1
  • 1
  • 1
  • Tagged with
  • 138
  • 138
  • 38
  • 26
  • 22
  • 19
  • 18
  • 18
  • 15
  • 12
  • 12
  • 12
  • 11
  • 11
  • 11
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

Argila: matéria-prima para cerâmica popular - três casos - Rio Real (BA), Apiaí (SP) e Taubaté (SP). / Clay: raw material for ceramics popular - three cases - Rio Real (BA), Apiaí (SP) and Taubaté (SP).

Anna Carolina Marques Ayres Calaresi 24 February 2014 (has links)
O presente trabalho tem como objetivo principal relacionar a utilização da argila, material de expressão artística e cultural a aspectos técnicos frequentemente ignorados pelos executores (artesãos artistas), a partir da análise de técnicas tradicionais de modelagem. Busca, portanto, compreender como a matéria-prima (argila), disponível para certa comunidade artesã, influenciou o desenvolvimento espontâneo de uma técnica de modelagem empregada em uma determinada região do Brasil, resultando em uma forma peculiar de expressão artística. A disponibilidade de um tipo de matéria-prima é um aspecto comumente negligenciado na análise de uma forma de expressão artística. Muitas vezes, em função das limitações tanto do material como da falta de conhecimento técnico, falhas do material são resolvidas com a utilização de técnicas desenvolvidas como fruto da experimentação e observação. Assim, objetiva investigar como as propriedades da argila são importantes na definição das características de um trabalho, na escolha do método de execução em suas diferentes fases. Como os executores conseguem superar certos problemas apresentados pelo material com o emprego de soluções experimentais. A metodologia abrange pesquisa bibliográfica, visita a campo para coleta de material para análise, caracterização do material, comparação entre resultados obtidos. Os resultados da pesquisa comprovaram que a matéria-prima utilizada por cada comunidade influencia o tipo de trabalho executado, promovendo a escolha de soluções estéticas e de modelagem adequadas às propriedades das argilas. Isto de certa forma inviabiliza a execução do trabalho com suas características particulares e autênticas em outra região, com uso de uma argila que não a disponível no local. Daí o caráter também documental do estudo, pois registra tanto a existência de uma matéria-prima finita e suas particularidades específicas, como também a técnica e a voz dessas pessoas, que de forma singular a utilizam como meio de expressão e subsistência. / The present work has as its main objective to relate the use of clay, artistic expression and cultural material technical aspects often ignored by the executors (artisans artists), from the traditional techniques of analysis modeling. Search, therefore, understand how the raw material (clay), available for certain artisan community, influenced the spontaneous development of a modeling technique employed in a particular region of Brazil, resulting in a peculiar form of artistic expression, because the availability of a kind of raw material is a commonly neglected aspect in the analysis of a form of artistic expression. Often, depending on the limitations of both the material and the lack of technical knowledge, \"failures\" of the material are resolved with the use of techniques developed as a result of experimentation and observation. Thus, aims to investigate how the properties of clay are important in defining the characteristics of a work, in choosing the method of execution in its different phases. As performers can \"overcome\" certain problems presented by the material with the use of experimental solutions. The survey results proved that the raw material used by each community influences the type of work performed, promoting the choice of aesthetic solutions and appropriate modeling the properties of clays. This somehow makes the execution of work with their particular characteristics and authentic in another region, with use of a clay that not available on site. Hence the documentary also character of the study, because registers both the existence of a story press and their specific particularities finite but also the technique and the voice of these people, that of singular form to use as a means of expression and livelihood.
42

Análise da influência das propriedades do material e parâmetros do processo na simulação numérica do processo de forjamento

Lenhard Júnior, Adalberto Luiz January 2007 (has links)
Este trabalho tem como objetivo investigar quais são os valores dos principais parâmetros que a literatura apresenta para o processo de forjamento a morno de precisão. Os parâmetros escolhidos são: curva de escoamento do SAE-1050M a frio e a quente, fator de atrito e o coeficiente de transferência de calor entre peça e ferramenta. Estipulou-se uma faixa de variação destes parâmetros, simulou o processo através do método dos elementos finitos com o uso do pacote MSC.Superform 2005 para os diferentes parâmetros e cruzou os resultados por meio do conceito de sensitividade. Os resultados cruzados são: força, trabalho, deformação e temperatura. Simulações são realizadas com variações dos parâmetros de entrada baseadas nos ensaios e levantamento bibliográficos. As respostas das simulações são adimensionalizadas com o uso do conceito de sensitividade, podendo assim, serem comparadas entre si. O fator de atrito e o coeficiente de transferência de calor entre peça e ferramenta não influenciam tanto na resposta como a curva de escoamento. / This work has as objective to investigate which values of key parameters are presented by the literature for the warm precision forging process. The chosen parameters are: hot and cold SAE-1050M flow stress curve, friction factor and heat transfer coefficient between workpiece and die. Stipulate a range of variation of these parameters, simulate the process through the finite elements method with the use of the package MSC.Superform 2005 with different parameters and cross the results with concept of sensitivity. The crossed results are: force, work, strain and temperature. Simulations are carried out with variations of the input parameters based on the bibliographical research and tests. The simulations output are nondimensionalised with the use of the sensitivity concept, thus being able, to be comparative between themselves. The friction factor and the heat transfer coefficient between workpiece and die do not influence as much as the flow stress curve.
43

Creating Digital Photorealistic Material Renders by Observing Physical Material Properties

Johansson, Simon January 2014 (has links)
When creating materials in computer graphics, the most common method is to estimate the properties based on intuition. This seems like a flawed approach, seeing as a big part of the industry has already moved to a physically based workflow. A better method would be to observe real material properties, and use that data in the application. This research delves into the art of material creation by first explaining the theory behind the properties of materials through a literature review. The review also reveals techniques that separate and visually presents these properties to artists, giving them a better understanding of how a material behaves. Through action research, an empirical study then presents a workflow for creating photorealistic renders using data collected with these techniques. While the techniques still require subjective decisions when recreating the materials, they do help artists create more accurate renderings with less guesswork.
44

The Process Influence on Strength Properties of an Austenitic Stainless Steel (254 SMO) / Processpåverkan på hållfasthet hos ett austenitiskt rostfritt stål (254 SMO)

Hellqvist, Anna January 2014 (has links)
This work has been performed at Outokumpu Stainless AB, QPE, in Degerfors where focus is on production of hot rolled tailor-made quarto plate in special stainless steel grades such as highly alloyed austenitics and duplex steel grades. After a period with low values in strength and a lot of deviations in tensile tests for the highly alloyed austenitic stainless steel, 254 SMO, there was a need to investigate what influence some parameters during process has on strength values. Process parameters during hot rolling and levelling have been examined to see if there is a connection between these and the strength. A statistical data base has been created to investigate the connection with strength. There has been experimental work involving two test plates in different dimensions to see how a double/extended heat treatment influence the sigma phase values and grain size, and if these can be connected to the strength values. The test plates have also been used to investigate how the position of the test coupon is affecting the tensile test result. Moreover, there have been tests performed in the cold plate leveller. The strength is a complex problem since there are many parameters that contribute to a variation in strength value. It is possible to see an influence from the investigated parameters, but their individual impact on strength varies. There are several indications in the results that the flatness seems to be a factor affecting the variation in strength. However, there is a need for more thorough investigations where the flatness can be measured to completely verify this / Det här arbetet har utförts på Outokumpu Stainless AB, QPE, i Degerfors där man inriktar sig på produktion av varmvalsad, skräddarsydd kvartoplåt i olika specialstål som höglegerade austeniter och duplexa stålsorter. Efter en period med låga värden i hållfasthet och många avvikelser i provning för ett höglegerat austenitiskt stål, 254 SMO, så fanns ett behov av att undersöka vissa parametrars inverkan på hållfastheten. Processparametrar vid valsning och riktning har undersökts för att se om det går att se ett samband mellan dessa och hållfastheten. Statistisk data har tagits fram för att undersöka sambandet med hållfastheten. Även experimentella försök har gjorts, främst på två testplåtar i olika dimensioner, för att se hur en dubbel/förlängd värmebehandling påverkar sigmafas och kornstorlek men även om dessa värden, genom försöken, kan kopplas till hållfasthetsvärden. Plåtarna har också använts till att se hur testresultatet påverkas av var i plåten som testkupongen tas ut. Dessutom har det gjorts försök i riktverket med olika parametrar. Hållfastheten är ett komplext problem att utreda eftersom det finns så många parametrar som ger en variation i resultaten. Det är möjligt att se en påverkan från flera av de undersökta parametrarna men deras individuella påverkan på hållfastheten varierar. Det finns många indikationer i resultaten som pekar på att planheten verkar vara en faktor som påverkar den variation som finns i resultat. Dock behövs det grundligare undersökningar där planheten kan mätas för att helt verifiera detta.
45

Asymmetric Large Area Model Biomembranes

Liu, Paige 08 May 2020 (has links)
All biological cell membranes maintain an electric transmembrane potential of around 100 mV, due in part to an asymmetric distribution of charged phospholipids across the membrane. This asymmetry is crucial to cell health and physiological processes such as intracell signaling, receptor-mediated endocytosis, and membrane protein conformation and function as well as active processes involving flippase and floppase proteins. Despite the biological significance, there are limited studies linking the consequences of lipid asymmetry to critical membrane properties and processes involving ion channels. One reason for this is the scarcity of reliable methods to create artificial membrane systems that incorporate both transverse lipid asymmetry and ion channels. Experimental artificial membrane systems incorporate essential cell membrane structures, namely the phospholipid bilayer, in a controllable manner where specific properties and processes can be isolated and examined in an environment much simpler than living systems. It is of particular interest to study asymmetry in transverse lipid composition across the phospholipid bilayer on such a system to probe the effects of the lipid composition and asymmetric arrangement of these lipids on the physicochemical properties of the membrane. By doing so, an understanding of how membrane asymmetry dictates membrane properties and in turn impacts cellular processes will be achieved. The primary goal of this thesis is to develop a platform for fabricating and characterizing compositionally controlled planar, free-standing, asymmetric membranes. This asymmetry was qualitatively demonstrated using a fluorescence quenching assay, and it has been quantified using a combination of anionic and zwitterionic lipids in concert with a patch-clamp amplifier system. Initial measurements of a transmembrane potential on a partially asymmetric bilayer were found to be between 10 and 25 mV. Increasing membrane charge asymmetry increases the offset voltage, as expected, and also modifies the stiffness of the membrane. These initial successes demonstrate a viable pathway to fabricate and quantitatively characterize asymmetric bilayers that can be extended to accommodate more complex membrane processes in the future.
46

Analýza rizik možností posuzování charakteristických hodnot vlastností stavebních materiálů / Risk analysis of the possibilities of evaluating characteristic values of building material properties

Boháč, Vlastislav January 2015 (has links)
The thesis is concerned with summarization of steps to determine of the characteristic values of building materials which are listed in European and Czech standards number 72 - Building raw materials, materials and products and number 73 - Design and construction of buildings. The aim of thesis is to describe differences and perform analysis of individual processes and propose the solution of these problems.
47

Relation Between the Material in Press Hardening Dies and Fully Martensitic Transformation : Sheet properties of thick 3D-sheets in small series production

Christensson, Jesper January 2020 (has links)
This report evaluates the influence of the die material on the cooling rate and martensitic transformation of press hardened sheets. The goal was to increase the thicknesses of sheets that can form fully martensitic microstructure when press hardened. To achieve this, a numerical- and an experimental method was used and results were compared to assess the impact of die material change. The tests were conducted with two die materials, a ductile cast iron according to standard EN‑GJS‑700‑2 and a casted steel according to standard EN 1.6220. Two sheet materials, Hardox400 and Hardox450, were press hardened and two different thicknesses were evaluated. Simulations have been designed with temperature dependent material properties based on data gathered from the literature survey. All simulations indicated an improved cooling rate over the entire temperature spectrum when changing from the iron die to the steel die.   An experimental procedure has been performed using two different dies, both planar and of approximately the same thickness. Thermocouples were used to obtain cooling curves of all sheets during quenching. Samples were taken from each sheet and the hardness, microstructure and the present phases were investigated.   The experiments concluded that the thinner sheets, when quenched, experienced an overall increase in cooling rate in the steel die compared with the iron die. A total reduction in cooling time by 37.5%-43,7% was observed over the entire temperature span. However, only the Hardox400 sheet fully formed martensite, as the cooling of the Hardox450 sheets still was not fast enough in either of the dies. For the thicker sheets, the experiments also indicated a reduction in total cooling time. The total cooling time was reduced by 23% when pressed in the steel die compared to the iron die. This improvement, however, was not observed at higher temperatures. At the critical temperature span between 800˚C and 500˚C, the sheet showed no improvements in cooling rate with the die material change. Both the hardness measurements and the microstructure evaluation of the thicker sheets indicated a pearlitic-martensitic microstructure. As both the simulations and experiments indicated similar improvements, the increase in cooling rate could be accredited to the die material change.  This concludes that the heat transfer properties of the die material affected the cooling characteristics of the process. It was also concluded that the thinner sheets experienced a reduced cooling time over the entire temperature spectrum with the die material change. The thicker sheet, however, only experienced a reduced cooling time in the lower temperature span. Thus, changing the die material did not affect the hardening of the thicker sheets. This ultimately resulted in an unsuccessful attempt to increase the possible thickness of sheets with fully martensite microstructure. The improvements observed for the thinner sheets, are however promising and could be further evaluated for another sheet material. / I denna avhandling har relationen mellan ett verktygmaterials kylningseffekt och genomhärdningsförmåga under presshärdning utvärderats, med målet att öka tjockleken på plåtmaterial som genomhärdar. För att åstadkomma detta har en numerisk undersökning och en experimentell undersökning utförts för att bedöma effekten av ett byte av verktygsmaterial. Undersökningarna utfördes med två verktygsmaterial, ett segt gjutjärn enligt standard EN‑GJS‑700‑2 och ett gjutet stål enligt standard EN 1.6220. Under testerna användes även två olika plåtmaterial, Hardox400 och Hardox450, i två olika tjocklekar. Simuleringen har utformats med relevanta temperaturberoende materialparametrar erhållna från teorin. Resultaten från simuleringarna påvisade att ett byte av verktygsmaterial gav snabbare kylning av all plåtar över hela det undersökta temperaturspannet. Den experimentella undersökningen har utförts med två olika pressverktyg, båda plana med likartad tjocklek. Temperaturgivare användes för att erhålla kylkurvor för plåtarna när de kyldes i verktygen. Hårdhet, mikrostruktur och erhållna faser undersöktes för varje plåt. Experimenten påvisade att de tunnare plåtarna kyldes snabbare i stålverktyget än i järnverktyget över hela temperaturspannet, och resulterade i 37,5%-43,7% kortare kyltider. Trots detta, var det endast Hardox400-plåten som genomhärdades, då kylningen av Hardox450-plåten inte var tillräckligt snabb i något av verktygen. Även de tjockare plåtarna uppvisade en totalt kortare kyltid. Kyltiden minskade med 23% i stålverktyget jämfört med järnverktyget. Denna förbättring observerades dock inte över hela temperaturspannet. Vid höga temperaturer kylde stålverktyget långsammare än järnverktyget. De släckta plåtarna erhöll en perlitisk/martensitisk struktur vid komplett svalning, oberoende av verktygsmaterial. Eftersom både simuleringarna och experimenten påvisade liknande förbättringar, kan den ökade kylhastigheten härledas till bytet av verktygsmaterial. Detta fastställer att värmetransportegenskaperna hos verktygsmaterialet hade en inverkan på kylningen i processen. Studien påvisade också att de tunnare plåtarna kyldes fortare över hela temperaturspannet vid materialbytet. De tjockare plåtarna uppvisade dock endast en kortare kyltid i det lägre temperaturspannet. Därmed förblev härdningen av de tjockare plåtarna opåverkad av materialbytet. Detta resulterade i att presshärdning av ökad plåttjocklek för det undersökta materialet inte lyckades. De observerade förbättringarna hos de tunnare plåtarna är dock mycket lovande och bör studeras vidare.
48

Effects of Infiltration Temperature, Time, and Gas Flow Rate on Material Properties of Carbon Infiltration Carbon Nanotubes

Sypherd, Shane Dirk 01 September 2019 (has links)
This work characterizes the material properties of carbon infiltrated carbon nanotube (CI- CNT) structures. The impacts of temperature, time, and hydrogen flow rates on the material prop- erties of modulus of elasticity and strength are examined and compared. Carbon infiltration levels are assessed through the use of SEM images to determine which parameters give the highest level of infiltration. Through the use of SEM, carbon capping is observed on samples infiltrated for longer times at 900 and 950◦ C, suggesting that the samples are not being infiltrated during the entire desired infiltration period at these temperatures. The highest material properties of modulus and strength were reached when infiltrating the carbon nanotube forests for 150 mins at 850◦ C with hydrogen flowing at 311 sccm (0.0115 m/s). With these parameters, a modulus of 20.4 GPa and strength of 289.8 MPa were attained. The poorest results were seen when the samples were infiltrated at 800◦ C, and is therefore not recommended as an infiltration temperature if high mod- ulus and strength are desired. Density is correlated to strength and modulus and it is seen that there is a strong correlation between higher strength and modulus with higher density.
49

Tool condition analysis and monitoring in cold rolling process

El Siblani, Ali January 2011 (has links)
This research is about a costly problem in the automotive industry due to tool fracture during the splines cold rolling of steel shafts. The objective is to study the cause of this failure and propose solutions that can be implemented in the workshop.The writing starts with a brief introduction of the companies involved in shafts production and problem solving. It introduces the cold rolling process and its advantages on splines manufacturing, and it goes through relevant material and process characteristics that help to determine the cause of tool fracture.In order to understand the process failure and production flow, it has been necessary to build up an Ishikawa diagram with possible tool fracture causes. After collecting and analysing the data about the machine tool, cold rolling process and work-piece and rolling tool materials, tests and experiments have been done.It has been considered that there is a rolling tool fatigue that causes tool fracture. Beside tool fracture, two more problems with production flow instability and the right side rolling tool have been detected. Testing the material hardness of the work-piece has shown continuous hardness fluctuations from the supplier. Rolling tool misalignment has been measured by using a vernier caliper measurement device. Rolling tools material hardness analysis shows that tool is very hard and it is possible to use a tougher material which responds better to cyclic loads.Leax has tried to solve the problem by testing another lubrication and tool coatings. A modal analysis test has been performed in order to find the natural frequency of the work-piece which possibly may lead to vibration and over loading one of the rolling tools.The conclusion that has been reached is that main cause of fracture is rolling tool fatigue due to cyclic loads and it is important to use other rolling tool material. The other two detected problems, production flow instability and rigth side rolling tool fracture, should be considered as a part of the problem in order to significantly increase tools life and stabilize production flow rate.
50

The Microstructure and Material Properties of the Epicentral Tendon-Vertebra Attachment in Rainbow Trout

MacMaster, Emily 11 November 2020 (has links)
Studies of the microstructure of tendon-bone attachments in mammals have shed light on their role in mediating efficient force transfer between tendon and bone, two tissues that differ vastly in their structure, composition, and material properties. Studies have also elucidated the importance of mechanical stimulation in maintaining tendon-bone attachment structures so that they may function successfully in dissipating mechanical stresses at the tendon-bone interface, to minimize the risk of tissue failure. Gross anatomical studies in fish have focused on identifying pathways of myomere contractile force transmission to the backbone of the fish, via connective tissue septa, to achieve body undulation. Little focus has been placed on how these connective tissues connect to the bone at the microscopic level to achieve force transfer. Moreover, whether or not these attachments are capable of undergoing remodeling in response to novel force regimes—which may influence their function—remains to be elucidated. First, we characterized the microstructure and material properties of the epicentral tendon-vertebra attachment in rainbow trout by conducting histology and tensile-testing. Individual collagen fibers of the epicentral tendon projected directly into the cancellous bone of the vertebra. We observed rostral-to-caudal trends in material properties for attachments found at different positions within the region spanning the dorsal and adipose fin, suggesting that attachments differed in their structure and/or composition at different positions along the backbone. Furthermore, the angle of the epicentral tendon with respect to the bone influenced the material properties and structural integrity of the attachments during tensile-testing, suggesting that attachments may be optimized to transfer force along particular angles. Second, we studied the effect of unloading on the material properties of the epicentral tendon-vertebra attachment by severing a subset of epicentral tendons on one side of rainbow trout. Severing of epicentral tendons had no effect on attachment material properties, suggesting that attachments did not undergo any alterations in structure and/or composition. We propose that the contiguous network of connective tissues in which the epicentral tendons are embedded as well as the fish’s gross musculature may have supported the maintenance of function of the epicentral tendon-vertebra attachments.

Page generated in 0.1017 seconds