In the presented Master’s thesis “Hardness differences compensation of components during profile rolling” are the effects of hardness oscillation of finished components considered. The effects are through the Design of Experiments method at various spline profiles and process options tested. The evaluation in Minitab software showed, that the reduction of roll diameter oscillation is through the process regulation based on rolling force difference possible.

<div>Aluminum alloy sheets are typically manufactured from cast slabs by multi-step rolling and annealing process. This process is very energy intensive, especially in the homogenization process after casting, which usually is conducted at 480 to 580 ℃ for up to 48 h. To reduce the </div><div>processing steps and energy, a shear-based single-step deformation process, large strain extrusion machining (LSEM), was used to create strips from AA6013-T6 with and without preheating of the workpiece. Continuous strips were obtained from this alloy with low workability. Flow patterns through the thickness of the strips exhibited primary shear with grains inclined steeply to the faces of the strips, modified to varying degrees by secondary shear from friction with the tools at the surfaces. Through control of the deformation parameters (strain, strain rate and temperature), a wide range of microstructure could be achieved. In high-temperature LSEM, dynamic recrystallization occurs at lower temperatures than in commercial hot rolling processes. </div><div><br></div><div>LSEM was performed directly on the as-cast AA6013 without homogenization. By appropriate combination of strain and strain rate, continuous strips were obtained in a single step without preheating directly from the as-cast workpiece. The highly deformed LSEM strip has enhanced workability. It can be cold rolled with at least 73% reduction in a single step without cracking. The strips were characterized by strong shear texture with partial {111} and <110> fibers. After annealing, a mixed texture containing simple shear texture and other texture develops. The annealed strips are expected to have better formability than commercial ones made by rolling.<br></div><div><br></div><div>In comparison, multi-step warm-rolling and cold rolling were performed on the as-cast AA6013. The as-cast material was preheated to 300 ℃ and rolled with 12% reduction per pass till the same effective strain as the LSEM. The warm-rolled strips were then cold-rolled with the same reductions as those on LSEM strips. The results showed that during warm rolling process, cracking occurs on the strips before reaching the same effective strain and the warm-rolled strips can only be further cold rolled with reduction less than 26% before cracking, compared with 73% reduction without cracking for LSEM strips.<br></div><div><br></div><div>Based on the simple shear LSEM process, a novel way to produce aluminum strip/sheet material is introduced. The alloys are cast into disk-shape workpiece and then transferred to the LSEM line. In this line, continuous strips/sheets are obtained in a single step at room temperature. The materials are then coiled if needed and cold rolled to the final gauge. Finally, the strips/sheets are solution treated for further deformation processing. In this method, the conventional homogenization and hot rolling, including reversing and multi-stand hot rolling, are replaced by a single-step LSEM process at room temperature.<br></div>

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

Heavy haul railway operations permit the transport of huge volumes at lower cost than other modes of transport. The low cost can only be sustained if the maintenance costs associated with such railway operations are minimised. The maintenance costs are mainly driven by wheel and rail damage in the form of wear and rolling contact fatigue (RCF). Low wear rates in the wheel-rail interface have resulted in an increase in the prevalence of rail RCF, thereby increasing rail maintenance costs. The aim of this study is to develop an approach to reduce rail RCF on South Africa’s iron ore export line by managing the worn wheel shape. This approach is developed by evaluating wheel and rail profile shapes that contribute the most to RCF initiation, studying the influence of suspension stiffness and rail profile changes as well as a redesign of the wheel profile. The influence of wheel and rail profile shape features on the initiation of rolling contact fatigue (RCF) cracks was evaluated based on the results of multibody vehicle dynamics simulations. The damage index and surface fatigue index were used as two damage parameters to assess the influence of the different features. The damage parameters showed good agreement to one another and to in-field observations. The wheel and rail profile shape features showed a correlation to the predicted RCF damage. The RCF damage proved to be most sensitive to the position of hollow wear and thus bogie tracking. RCF initiation and crack growth can be reduced by eliminating unwanted shape features through maintenance and design and by improving bogie tracking. Two potential mitigation measures had been adapted from those published in literature to reduce RCF. The mitigation measures involved changes in suspension stiffness to spread wheel wear across the tread and the use of gauge corner relief rail profiles. These mitigation measures were evaluated by means of multibody dynamics and wear maintenance costs. These mitigation measures, however, did not prove to be successful in reducing RCF initiation while maintaining a low wheel wear rate. The current operating conditions on South Africa’s iron ore line, although still not optimal overall, were found to be better in terms of their wear and RCF performance than the two proposed RCF mitigation measures. Based on the finding of the study on two RCF mitigation measures it was recommended that a conformal wheel profile be developed to spread the wheel wear across the tread to reduce the occurrence and propagation of RCF cracks, while still maintaining low wheel wear rates. A comparative study of this new wheel profile design and the current wheel profile design was therefore performed using multibody dynamics simulation together with numerical wheel wear and RCF predictions. The advantages of the conformal wheel profile design were illustrated by evaluating the worn shape and resulting kinematic behaviour of the conformal design. The conformal design had a steadier equivalent conicity progression and a smaller conicity range compared with the current wheel profile design over the wheel’s wear life. The combination of a conformal wheel profile design with 2 mm hollow wear and inadequate adherence to grinding tolerances often result in two-point contact, thereby increasing the probability of RCF initiation. The conformal wheel profile design was shown to have many wear and RCF benefits compared with the current wheel profile design. However, implementation of such a conformal wheel profile must be accompanied by improved rail grinding practices to ensure rail profile compliance. Based on these findings an approach is proposed where the conformal wheel profile design together with improved compliance of the in-service rail profiles to the target rail profile are implemented. This has the potential to reduce RCF initiation on South Africa’s iron ore export line. / Thesis (PhD)--University of Pretoria, 2017. / Mechanical and Aeronautical Engineering / PhD / Unrestricted

in English Ondřej Kincl 21 May 2020 Rolling turbine is a small hydraulic turbine invented by Doc. Ing. Miroslav Sedláček CSc. in 1998. This turbine is bladeless, exhibits various interesting behaviour and operates on the basis of a yet unknown hydraulic principle. This thesis attempts to find an explanation using incompressible Navier- Stokes equations. We will introduce the concept of drag inversion - the idea that fluid force in rolling turbines is a positive feedback to the motion itself. This is explained in a simplified model using analytical methods. These results are then verified in a numerical simulation.

VLIV VZTAHU DÉLKY DOLNÍ KONČETINY A VELIKOSTI RÁFKU NA PSYCHOFZIOLOGICKOU ODEZVU ORGANISMU Cíle: Cílem této práce je posoudit vliv délky dolní končetiny (DK) na psychofyziologickou odezvu organismu při jízdě na horském kole s odlišnými velikostmi ráfků. Metody: Soubor probandů tvořilo 20 mužů ve věku 26,4 ± 4,2 let. Jednalo se o experiment. Psychofyziologická odezva byla stanovena na základě výkonu (zajetého času), tepové frekvence a subjektivním hodnocení jízdních vlastností horského kola a vlastního vynaloženého úsilí hodnoceného na Borgově škále. Ke kontrolní analýze při testování byl použit přístroj MetaMax 3B. Testovány byly tři velikosti ráfků o stejné šíři plášťů. Jízdy byly realizovány na 800 m dlouhém okruhu. Testované osoby absolvovali každou jízdu s individuálně zvoleným fixním převodem v poloze v sedle s maximálním možným úsilím. Výsledky: Při jízdě na různě velkých ráfcích jsme u skupiny č. 2 (85 -90 cm DK) shledali velký rozdíl (P = 0,016) v dosažených časech při jízdě na různě velkých ráfcích. U skupiny č. 1 jsme shledali významné rozdíly v průměrné tepové frekvenci (P = 0,010), který činil 3 tepy a u subjektivního hodnocení vlastního vynaloženého úsilí pomocí Borgovy škály jsme se pohybovali na hranici významnosti (P = 0,060). Skupina č. 3 (97 - 101 cm DK) se pohybovala na hranici...

Introduction 100Mo target design is key to commercially viable large scale cyclotron production of 99mTc. The target back plate supporting the 100Mo must be chemically inert to the target dissolution conditions but ideally it should also be able to dissipate the high thermal loads of irradiation, not contaminate target substrate with radionuclidic by-products, and be adequately inexpensive to allow for single use. Aluminum was selected as our target support as it satisfies these requirements. Our process entails rolling 100Mo powder into a foil of desired thickness, and then diffusion bonding [1] the foil onto an aluminum back plate. The 100Mo targets were designed to be 20×80×0.1 mm to match our TR24 cyclotron’s proton beam profile and energy. Efforts are currently underway to scale up the process to allow for simultaneous production of multiple targets at once. Material and Methods The crude enriched 100Mo foil (99.815% enrichment) was made from 100Mo powder using a horizontally mounted rolling mill and an aluminum hopper. The crude foil was rolled repeated-ly, and the space between the rollers gradually reduced until the thickness of the foil was changed from an initial thickness of 0.3 mm to a thickness of 0.1 mm. The rolled 100Mo foil was annealed under reducing atmosphere and then bonded to the aluminum target plate support under inert atmosphere in a heated press at 500 °C. Results and Conclusion By rolling 100Mo foils from powder we were able to produce uniform foils with an average density of > 98 % compared to the maximum theoretical density of 100Mo (n = 5) and thicknesses of roughly 0.1 mm. All foils produced were the desired 20 mm width (i.e. limited by the width of the opening of the hopper) and trimmed to the desired 80 mm length. The annealing process was necessary due to the brittleness of the un-annealed rolled foil and the difference in the thermal expansion coefficients of molybdenum and aluminum which caused un-annealed foils in previous experiments to crack and break off during pressing (n = 10). Surface preparation of the aluminum support plate was also found to play a critical step in the efficiency of the bond, and continuing effort to scale the above de-scribed procedure to mass produce 100Mo tar-gets is ongoing. Targets have undergone preliminary testing to 250 μA.

Operation Rolling Thunder was a United States led operation, with the political aims of interdicting and preventing the North Vietnamese support of the South Vietnam rebellion, during the later stage of the Vietnam war. Despite being a superpower, Operation Rolling Thunder failed, and the USA lost the war. In this essay, the air power theorists John A. Warden and Robert A. Pape, and their theories regarding how air power should be used to reach success, are used to analyze this failure. The use of these theories in a parallel manner enables to comprehend empirical sources and in turn recognize anomalies in the decision making and missteps of the American leadership. By keeping the case of Rolling Thunder in focus and thereby try and understand what happened, the aim is to create an understanding for why the potent power of the US Air Force made an inadvertent turn despite exercising air superiority throughout most of the operation. This examination concludes that there were three deciding factors in the American failure, which are: (i) absence of efficient attacks against the North Vietnamese leadership, (ii) lack of correlation between strategy and political aim, (iii) lack of experience and communication within the American leadership.

The last seven hot rolling passes of the ferritic stainless steels (FSS) AISI 430 and AISI 433 (the latter an Al-added variant of 430) were simulated on Gleeble-1500D® and Gleeble-3800TM® thermo-mechanical simulators to investigate the effect of temperature, strain rate and inter-pass time on the development of texture in these steel grades and its subsequent influence on ridging. The compression tests were carried out over a wide range of strain rates (0.1 s-1 to 5 s-1, 25 s-1 and 50 s-1) and temperatures (1100 to 820 oC) with different inter-pass times (2 s, 10 s, 20 s and 30 s). The transition temperature from dynamic recrystallization (which may introduce a texture change) to dynamic recovery (in which no texture changes are expected) was determined by examining the relationship between the mean flow stress and the deformation temperature in multi-pass tests. Both macrotexture (XRD) and microtexture (EBSD) analyses were employed to characterise and study the texture present in these steels. It was found that the texture in the central layer of the compressed sample is a strong recrystallization-type. The through-thickness textural and microstructural banding was found to be responsible for ridging in these grades of stainless steels. Dynamic recrystallization which promotes the formation of the desired ã-fibre texture leading to high ductility, formability and eventually reduction or elimination of ridging, was found to occur in both AISI 430 and AISI 433 at high temperatures, low strain rates and longer inter-pass times with multi-pass testing. Generally AISI 433 has a stronger gamma texture developed than the AISI 430 when hot rolled under similar conditions, which leads to improved ductility and less ridging in AISI 433 than AISI 430. / Dissertation (MSc)--University of Pretoria, 2012. / Materials Science and Metallurgical Engineering / unrestricted

This study will apply the Capital Asset Pricing Model (CAPM) to help understand the relationship between traded real estate companies and their respective financial markets. The aim will be to quantitatively explain the link between real estate companies holding different asset types within their portfolio and their traded financial markets using betas from CAPM. Some companies have preferences towards one type of real estate assets; which could be referred to as "portfolio bias." On the other hand some companies have a portfolio bias towards diversification and hold a portfolio of diversified assets. This study will examine how diversification plays a role in both correlation to the market and overall return. The idea is that a real estate company holding a more diversified portfolio performs more like the market and therefore acts more like the market portfolio made up of value weighted stocks and securities within the financial market. A more diversified portfolio should pose less risk and perform better over the long term which many studies have shown to be the case in financial markets. This study will also explore the connection between underlying asset types using residential, retail and diversified assets compared to their traded financial markets to determine the role of portfolio bias.