V současné době se zvyšuje potřeba rozvoje agilních výrobních postupů, které lze snadno přizpůsobit neustálému zavádění nových produktů na trh. Jednobodové inkrementální tváření je nový, inovativní a proveditelný tvářecí proces s jednoduchým uspořádáním. Proces se provádí při pokojové teplotě (tváření za studena) a vyžaduje CNC stroj, nástroj s kulovou hlavou a jednoduché příslušenství pro uchycení obrobku plechu. V samotném procesu jde o přírůstkové formování, řízené CNC programem. Plastická deformace je lokalizována pod formovacím nástrojem takže plech je tvářen souhrnem pohybů lokální plastické zóny. Tento proces je zdlouhavý a proto se hodí pouze pro prototypovou výrobu nebo pro malé výrobní dávky. Na druhé straně umožňuje vyšší tvářitelnost ve srovnání s konvenčními procesy tváření, umožňuje použití levných nástrojů a také je charakterizován krátkou dobou od návrhu po výrobu produktu. Tato práce je výsledkem mezinárodní spolupráce Danmarks Tekniske Universitet v Lyngby a Instituto Superior Técnico v Lisabonu. Práce začíná krátkým hodnocením dílčích tvářecích procesů, pokračuje představováním jednobodového inkrementálního tváření a identifikací jeho praktických aplikací. Teoretická část obsahuje přehled nového rámce pro jednobodové inkrementální tváření, který je vytvořen na základě analýzy styku třecích sil. Praktická část projektu poskytuje úplný popis experimentálních technik použitých pro charakterizaci materiálů a stanovení limitů tvářitelnosti, dále se analyzuje vliv různých vstupních parametrů procesu (poloměru nástroje, tepelné zpracování materiálu obrobku, druh maziva,...). Tato část také obsahuje přehled experimentálního uspořádaní procesu jednobodového inkrementálního tváření i krátký popis CAD / CAM vývoje tří testovacích modelů. Poté jsou popsány v samostatné kapitole výsledky pozorování a analýzy hlavních parametrů procesů, které ovlivňují tvařitelnostní limity v jednobodovém inkrementálním tváření v souvislosti s aplikovaným teoretickým rámcem. Výsledky experimentů z časti objasňují probíhající mezinárodní diskusi kolem tvářitelnosti mechanismu jednobodového inkrementálního tváření vzhledem k tradičním metodám tváření. Jako logické pokračování prováděných experimentů, byla práce rozšířena na více-stupňové jednobodové inkrementální tváření, které umožňuje tváření součástek (kalíšku) se svislými stěnami ve více krocích. Za účelem objasnění procesů spojených s tímhle procesem byly navrženy a ve čtyřech krocích vyrobeny dva experimentální modely. Hlavním přínosem této práce k více-stupňovému jednobodovému inkrementálnímu tváření byla úspěšná výroba součásti s nekruhovým průřezem a kolmými stěnami. S cílem aplikovat celkové znalosti získáných v předchozích částí práce byla vyrobena prototypová součást. Popis designu a vývoje prototypu je součástí práce. V neposlední řadě jsou celkové závěry uvedené v poslední kapitole. Předpokládá se, že tato práce přizpívá k lepšímu pochopení mechanismu jednobodového inkrementálního tváření.

Global warming and air pollution are the major problems facing the world today. Therefore strict environmental legislation on the emission of harmful gases from motor vehicles has forced the automobile industry to search for alternative materials or new materials for exhaust systems. In order to produce cleaner exhaust gases, the exhaust temperature needs to be increased to approximately 900oC. Therefore, exhaust manifolds are exposed repeatedly to hot gases as they are nearest to the engine requiring good oxidation resistance, thermal fatigue properties, cold workability and weldability. One such material to meet the above characteristics is AISI 441 ferritic stainless steel, a dual stabilised Ti and Nb ferritic stainless steel. Ti and Nb are added to stainless steel to stabilise C and N due to their high tendency to form carbonitrides (Ti,Nb)(C,N) and laves phase (Fe2Nb) and Fe3Nb3C. With 18% Cr content, this steel has a good corrosion resistance at elevated temperatures. Included in many applications of this steel are those requiring deep drawing and related forming operations. However, the drawability and stretchability of ferritic stainless steels is inferior to that of the more expensive austenitic stainless steels. For instance, Columbus Stainless has experienced ridging/roping problems at times during the manufacturing process of type AISI 441 ferritic stainless steel. It is believed that this problem is related to crystallographic texture of materials which have effect on formability. The R-value in FSS can be improved through optimisation of chemical composition, which includes reducing the carbon content, and processing conditions such as reducing the slab reheating temperature, increasing annealing temperature and refining the hot band grain size. Therefore the aim of this research project was firstly to investigate effect of amount of cold reduction and annealing temperature on texture evolution and its influence on formability. The as received 4.5 mm hot band steel was cold rolled by 62, 78 and 82% reductions respectively followed by isothermal annealing of each at 900oC, 950oC and 1025oC for 3 minutes. Orientation distribution function (ODF) through X-ray diffractometer (XRD) measurement was used to characterise the crystallographic texture formed in the steel using PANanalytical X’Pert PRO diffractrometer with X’celerator detector and variable divergence. Microstructures were characterised using optical microscopy and scanning electron microscope (SEM). The results show that steels that received 78% cold reduction and annealed at 1025oC recorded the highest Rm-value and lowest ΔR-value which enhances its deep drawing capability. In addition, this steel showed the highest intensity of shifted γ-fibre, notably {554}<225> and {334}<483>. It can therefore be concluded that the γ-fibre which favours deep drawing, is optimal after 78% cold reduction and annealing at 1025oC. The second objective was to investigate the effect of (Nb+Ti) content on the crystallographic texture and the subsequent formability and ridging severity. AISI 441 ferritic stainless steel with different amount of (Nb+Ti) content was used i.e. Steel A (0.26Nb+0.2Ti), Steel B (0.44Nb+0.15Ti) and steel C (0.7Nb+0.32Ti). After a strain of 10%, steels A exhibited the least resistance against surface ridging with average roughness Ra of 1.5 μm followed by steels B with an average roughness Ra of 1.1μm. Steel C showed the highest resistance to ridging with an average roughness Ra of 0.64 μm. This was attributed to the increase in carbonitrites (NbTi)(C,N) due to increased (Nb+Ti) content which acted as nucleation sites for γ-fibre. / Dissertation (MEng)--University of Pretoria, 2013. / gm2014 / Materials Science and Metallurgical Engineering / unrestricted

Reducing the weight of the truck vehicle conveys more cargo to be carried by thetrailer. This has a significant impact on the efficiency of the transport lowering both the total cost of cargo moved and the total carbon dioxide emitted. Half of the body in-white weight of a truck is comprised out of panels made out of thin mild forming steel which cannot be made thinner to reduce weight due to the lowered stiffness it would entail. Sandwich materials have a high stiffness to weight ratio and would for the same panel thickness as regular forming steel have a comparable bending stiffness but lowered weight. This master thesis is intended to be a preliminary study for Scania CV AB on sandwich materials and its potential use as lightweight panels in their trucks. With the intention of investigating whether a commercial sandwich material is capable of filling the role as outer panels of a truck, comparative tests regarding significant matters such as forming and painting was made on identically manufactured demonstrators comparing a sandwich material and a regular forming steel material. The tests identified weaknesses in the current manufacturing process for parts of a sandwich material. Such limitations are problems with painting and joining due to isolated cover sheets, forming problems revealing sink marks likely due to different spring back of the material and hemming flaws due to inadequately optimized hemming technique and anisotropy. Now that more knowledge of sandwich materials has been gained, counter measures for these findings can be made in order to take another step towards lowering the weight of the truck and a more efficient way of transporting goods. / Genom att minska vikten på lastbilen frigörs mer last att bäras av släpvagnen. Detta har en betydande inverkan på effektiviteten hos transporten som sänker både den totala kostnaden för transporterad last och de totala koldioxidutsläppen. Hälften aven lastbils rena karossvikt består av paneler gjorda av tunt mjukt formningsstål vilke tinte kan bli tunnare för att minska vikten på grund av den sänkta styvheten som detskulle medföra. Sandwichmaterial har en hög styvhet till viktförhållande och skulle församma paneltjocklek som vanligt formningsstål ha en jämförbar böjstyvhet men sänkt vikt. Denna uppsats är avsedd att vara en preliminär studie för Scania CV AB om sandwichmaterial och dess potentiella användning av lättvitkspaneler i lastbilar.Med avsikt att undersöka huruvida ett kommersiellt sandwichmaterial kan fylla rollen som lastbilens ytterpaneler utfördes jämförande tester med avseende på signifikanta frågor såsom formning och målning på identiskt tillverkade demonstratorer som jämförde ett sandwichmaterial och ett vanligt formningsstål. Testerna identifierade svagheter med materialet samt hur processen behöver anpassas för att kunna använda sandwichmaterialet i rådande tillverkningsprocess. Identifierade problem var bland annat problem med målning och sammanfogning på grund av isolerade ytterskickt i sandwichmaterialet, problem med formning som gav upphov till limdragningar som troligen beror på materialets olika återfjädring samt falsningsfel på grund av otillräckligt optimerad falsteknik och anisotropi. Nu när mer kunskap om sandwichmaterial erhållits kan motåtgärder för de funna resultaten undersökas för att ta ytterligare ett steg mot att sänka lastbilens vikt och därmed få ett effektivare transportmedel.

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Dans ce projet, le matériau est l'alliage de magnésium AZ31-O en tôle. L'épaisseur de tôles est de 1,2 mm. Les essais de traction à chaud sont réalisés afin d'étudier la ductilité de l'alliage de magnésium AZ31-O, la température et l'influence la vitesse de déformation sont incluses dans tous les tests. Le résultat d'analyse montre que la ductilité est renforcée avec une température croissante et une vitesse de déformation décroissante, le phénomène d'adoucissement est évident à la température élevée. La propriété anisotrope n'est pas considérée dans ce projet. Les essais Nakazima à chaud avec le poinçon d'hémisphère sont réalisés pour étudier la formabilité de l'alliage de magnésium AZ31-O. Enfin, la FLD (Forming Limit Diagram) est identifiée et les comparaisons montrent que la formabilité est préférable à une température plus élevée. En outre, les prédictions des limites de formage sont effectuées dans le modèle M-K. La comparaison montre clairement avec la prédiction théorique ne convient pas avec l'expérience. Les simulations des éléments finis sont effectuées pour un emboutissage par poinçon hémisphérique et un emboutissage en croix. Tout d'abord, les simulations d'emboutissage de poinçon hémisphérique sont réalisés sur FORGE® et sur ABAQUS®. Les résultats des simulations de FORGE et de ABAQUS sont comparés afin d'étudier la différence de divers codes de simulation des éléments finis. Deuxièmement, le comportement de d'endommagent est étudié dans FORGE par modèle d'endommagement Lemaitre. Enfin, la simulation d'emboutissage en croix qui est un benchmark de la conférence 2011 NUMISHEET est réalisée avec FORGE. La charge de poinçon, l'épaisseur et la distribution de température sont obtenues et comparées pour chaque simulation. En outre, ces résultats de la simulation de benchmark (FORGE) sont également comparés à d'autres logiciels de simulation en conférence. Les résultats des analyses détaillées sont présentés dans cette thèse. / In this project, the material is AZ31-O magnesium alloy sheet. The sheet thickness is 1.2mm. Warm tensile tests are performed to study ductility of AZ31-O magnesium alloy, the temperature and strain rate influence are included in all tests. The analysis result shows the ductility is enhanced with temperature increasing and strain rate decreasing, and the softening phenomenon is obvious at high temperature. The anisotropic property is not considered in this project. Warm Nakazima tests with hemisphere punch are performed to study formability of AZ31-O magnesium alloy. Finally, the FLD (Forming Limit Diagram) is identified and the comparisons distinctly show that the formability is better at higher temperature. Moreover, the forming limits predictions are performed in M-K model. The comparison clearly shows the theoretical prediction do not fit well with experiment. Finite element simulations are performed for a hemisphere punch deep drawing and a cross-shaped deep drawing. Firstly, the hemisphere punch deep drawing simulations are performed in FORGE® and ABAQUS®. The simulation result from FORGE and ABAQUS are compared in order to study the difference of various finite element simulation codes. Secondly, the damage behavior is studied in FORGE by Lemaitre damage model. Finally, the cross-shaped deep drawing simulation which is a benchmark of NUMISHEET 2011 conference is performed with FORGE. The punch load, thickness and temperature distribution are obtained and compared for each simulation. Furthermore, this benchmark simulation results (FORGE) are also compared with other various simulation software in conference. The detailed analysis results are presented in this thesis.

Esta tese tem por objetivo determinar a estampabilidade de chapas de alumínio 5083 O processadas pelo processo de fricção e mistura (PFM). Para atingir os objetivos propostos o processo de fricção por mistura foi estudado e uma ferramenta de soldagem PFM construída, a verificação da qualidade da solda foi realizada com metalografia da região processada para verificar a presença de vazios, obtidas as melhores condições a superplasticidade através do processo PFM é estudada com os ensaios de tração a quente e de saltos. Ensaios de tração a frio foram realizados nos corpos de prova com o processamento e sem o processamento com o objetivo de obter a curva tensão versus deformação do material processado e sem processamento. Foi efetuado o ensaio de microdureza da região soldada. A estampabilidade das chapas foi verificada através do ensaio de expansão hidrostática e empregadas na determinação da conformabilidade das chapas processadas e sem processar. Os ensaios de expansão hidrostática foram realizados em software de elementos finitos com o objetivo de comparar os resultados práticos e teóricos. Este estudo simulou pelo método dos elementos finitos a determinação da curva limite de conformação de chapas de alumínio 5083 O processadas através do processo PFM. A simulação de elementos finitos implicou em utilizar o método não linear e os softwares MSC MARC e Abaqus para simulação. Determinou-se neste estudo que a resistência à tração de chapas após processo PFM é 30% maior do que sem processamento, a estampabilidade à frio das chapas manteve-se a mesma. Os testes práticos determinaram que os softwares Abaqus e MSC MARC possuem boa aproximação para o teste de expansão hidrostática à frio. O Software Abaqus apresentou dificuldades para convergir e tempo de processamento muito superior ao MSC MARC nos estudos de expansão hidrostática à frio e na condição superplástica. Através dos ensaios de saltos determinou-se que a condição 328 rpm e 65 mm/min possui coeficiente de sensibilidade à taxa de deformação m muito superior ao do alumínio 5083 O sem PFM, isto resultou em uma melhor distribuição de espessura da chapa após o ensaio de expansão hidrostática superplástico em software. / The aim of this study is to determine the sheet metal formability of 5083 O aluminum sheets after friction stir processing \"FSP\". To achieve the proposed objectives the friction stir processing was be reviewed and modeled in order to enable the design and manufacture of a proper FSP tool. The quality of the process was carried out through metallographic tests of the FSP region looking for the presence of voids. The best conditions for plasticity and superplastic forming after FSP was studied by means of an approach of jump steps in the hot tensile tests, looking for a coefficient of strain rate sensitivity. The micro hardness tests and tensile tests at room temperature were carried out for the specimens with and without FSP processing in order to characterize their material mechanical behavior. The formability of the FSP blanks was evaluated through Bulge tests. The results enable to plot Forming Limit Curves friction stir processed blanks after FSP and without FSP. The numerical simulation of the Free Bulge tests was carried out using a Finite Element Method model in order to compare the numerical theoretical and experimental practical results. The numerical simulation approach allows for the determination the forming limit curve of 5083 O aluminum sheets processed by the FSP process. The Finite Element Method modeling and simulation have employed two nonlinear FEM codes: the MSC MARC and Abaqus were compared as software for the simulations. The Yeld Strength of specimens with FSP increased 30% in comparison with specimens without FSP in cold tensile tests, the formability of shapes with and without FSP was de same. The practical tests showed that Abaqus and MSC MARC results has a good approach, the processing time in Abaqus was much greater than in MSC MARC, Abaqus had convergence problems when contact condition is applied. Through the jump tensile tests the 328 rpm and 65 mm/min condition showed a m factor much higher in comparison with condition without FSP in AA 5083 O, this results led in a better thickness distribution after the superplastic bulge test in software.

Esta tese tem por objetivo determinar a estampabilidade de chapas de alumínio 5083 O processadas pelo processo de fricção e mistura (PFM). Para atingir os objetivos propostos o processo de fricção por mistura foi estudado e uma ferramenta de soldagem PFM construída, a verificação da qualidade da solda foi realizada com metalografia da região processada para verificar a presença de vazios, obtidas as melhores condições a superplasticidade através do processo PFM é estudada com os ensaios de tração a quente e de saltos. Ensaios de tração a frio foram realizados nos corpos de prova com o processamento e sem o processamento com o objetivo de obter a curva tensão versus deformação do material processado e sem processamento. Foi efetuado o ensaio de microdureza da região soldada. A estampabilidade das chapas foi verificada através do ensaio de expansão hidrostática e empregadas na determinação da conformabilidade das chapas processadas e sem processar. Os ensaios de expansão hidrostática foram realizados em software de elementos finitos com o objetivo de comparar os resultados práticos e teóricos. Este estudo simulou pelo método dos elementos finitos a determinação da curva limite de conformação de chapas de alumínio 5083 O processadas através do processo PFM. A simulação de elementos finitos implicou em utilizar o método não linear e os softwares MSC MARC e Abaqus para simulação. Determinou-se neste estudo que a resistência à tração de chapas após processo PFM é 30% maior do que sem processamento, a estampabilidade à frio das chapas manteve-se a mesma. Os testes práticos determinaram que os softwares Abaqus e MSC MARC possuem boa aproximação para o teste de expansão hidrostática à frio. O Software Abaqus apresentou dificuldades para convergir e tempo de processamento muito superior ao MSC MARC nos estudos de expansão hidrostática à frio e na condição superplástica. Através dos ensaios de saltos determinou-se que a condição 328 rpm e 65 mm/min possui coeficiente de sensibilidade à taxa de deformação m muito superior ao do alumínio 5083 O sem PFM, isto resultou em uma melhor distribuição de espessura da chapa após o ensaio de expansão hidrostática superplástico em software. / The aim of this study is to determine the sheet metal formability of 5083 O aluminum sheets after friction stir processing \"FSP\". To achieve the proposed objectives the friction stir processing was be reviewed and modeled in order to enable the design and manufacture of a proper FSP tool. The quality of the process was carried out through metallographic tests of the FSP region looking for the presence of voids. The best conditions for plasticity and superplastic forming after FSP was studied by means of an approach of jump steps in the hot tensile tests, looking for a coefficient of strain rate sensitivity. The micro hardness tests and tensile tests at room temperature were carried out for the specimens with and without FSP processing in order to characterize their material mechanical behavior. The formability of the FSP blanks was evaluated through Bulge tests. The results enable to plot Forming Limit Curves friction stir processed blanks after FSP and without FSP. The numerical simulation of the Free Bulge tests was carried out using a Finite Element Method model in order to compare the numerical theoretical and experimental practical results. The numerical simulation approach allows for the determination the forming limit curve of 5083 O aluminum sheets processed by the FSP process. The Finite Element Method modeling and simulation have employed two nonlinear FEM codes: the MSC MARC and Abaqus were compared as software for the simulations. The Yeld Strength of specimens with FSP increased 30% in comparison with specimens without FSP in cold tensile tests, the formability of shapes with and without FSP was de same. The practical tests showed that Abaqus and MSC MARC results has a good approach, the processing time in Abaqus was much greater than in MSC MARC, Abaqus had convergence problems when contact condition is applied. Through the jump tensile tests the 328 rpm and 65 mm/min condition showed a m factor much higher in comparison with condition without FSP in AA 5083 O, this results led in a better thickness distribution after the superplastic bulge test in software.

Shape memory alloys are a class of alloys that display the unique ability to undergo large plastic deformations and return to their original shape either through the application of heat (shape memory effect) or by relieving the stress causing the deformation (superelastic effect). This research takes advantage of the unique characteristics of shape memory alloys in order to provide a moment resisting connection with recentering capabilities. In this study, superelastic Nitinol, a nickel-titanium form of shape memory alloy that exhibits a flag-shaped stress versus strain curve, is used as the moment transfer elements within a partially restrained steel beam-column connection. Experimental testing consists of a one-half scale interior connection where the loading is applied at the column tip. A pseudo-static cyclic loading history is used which is intended to simulate earthquake loadings. The energy dissipation characteristics, moment-rotation characteristics, and deformation capacity of the connection are quantified. Results are then compared to tests where A36 steel tendons are used as the moment transfer elements. The superelastic Nitinol tendon connection showed superior performance to the A36 steel tendon connection, including the ability to recenter without residual deformation.