Modelling of rolling contact fatigue for rail materials being subject to severe plastic deformation

Modern railway systems are a beneficial way of transport. However, the operation requires maintenance to compensate for rail degradations. Key issues of degradation regard severe plastic deformation and rolling contact fatigue, which lead to the formation of cracks. A better understanding contributes to improve maintenance and operations. Numerical simulations offer ways to predict these degradations. State of the art for the simulation of solid mechanics is the Finite Element Method. An inherent limitation, though, is the basic assumption that the material is a continuum. Discontinuities like cracks violate this assumption. Thus, alternatives like Discrete Element Method models and Peridynamics were developed recently. These methods describe the material by a modular assembly of elements. This arrangement allows for a better modelling of discontinuities. Though, modelling of rolling contacts is a case where compressive loads dominate. This fact challenges discrete modelling approaches due to the common assumption that the failure of an element implies its removal. Another challenge models of this type face regards the validation of rolling contact fatigue. The aim of this work was to develop a discrete element model, which is optimised for the rolling contact application. For this reason, it was called the "Discrete Element Rolling Contact" model. Based on a linear-elastic model, a fatigue capability was introduced. This capability was transferred to the set-up of the rolling contact, which highlighted the first limitation stated above. In order to address this issue, a solution was developed and validated to calibrate the model to crack closure. Experimental results indicate that the fatigue crack growth behaviour of rails is governed by the severe plastic deformation the materials are subject to. For this reason, data of undeformed and deformed materials was parameterised and validated. A method to interpolate materials of varying degrees of deformation was introduced. Further, a method to transfer the material parameters to other materials of similar strength was developed. The result was a material library which is available for the model. In order to transfer the fatigue parameters to the rolling contact condition, a set-up to model the behaviour of highly shear deformed material was introduced. In this way, a drawback of the adopted fatigue law was highlighted, which emphasised the requirement to weight the influence of compressive strains. Finally, a procedure for the validation of the rolling contact model was proposed. In this work, a novel rolling contact fatigue model and a procedure for validation are presented, that consider the anisotropy of severe plastic deformation. With regard to the validation of discrete rolling contact models, the proposed procedure delivers a contribution that addresses key aspects that are not matured yet. These aspects, however, are critical for the development of dependable discrete models to predict rolling contact fatigue

Modernisierung eines Gasturbinenprüfstandes

Der Inhalt dieser Arbeit umfasst einen von mehreren Modernisierungsschritten eines Kleingasturbinen-Prüfstandes. Bei der Kleingasturbine handelt es sich um eine ROVER 1S60 des Instituts Energietechnik und Thermodynamik der TU Wien. Bei der Modernisierung wurde die Messtechnik erneuert, und eine neue Leistungsbremse angeschlossen, was jedoch nur dokumentiert wurde, und nicht Teil der Arbeit ist. Weiters wurde ein Betriebsmanual erstellt, mit dem die Maschine sicher betrieben werden kann.The thesis is about the upgrade of a stationary gas turbine testbed used by the Vienna Technical University / Institute for Energy Technology and Thermodynamics. The testbed uses a ROVER 1S60 which was developed for low-power applications. In the diploma thesis the renewal of measurement instruments, and the influence on operation of the new eddy current brake are discussed. Further an operation manual is added to the thesis in order to operate the testbed in a correct and safe way.von Markus JanuschewskyAbweichender Titel laut Übersetzung der Verfasserin/des VerfassersWien, Techn. Univ., Dipl.-Arb., 2009(VLID)160955

Upgrade of a gas turbine testbed

Abweichender Titel laut Übersetzung der Verfasserin/des VerfassersDer Inhalt dieser Arbeit umfasst einen von mehreren Modernisierungsschritten eines Kleingasturbinen-Prüfstandes. Bei der Kleingasturbine handelt es sich um eine ROVER 1S60 des Instituts Energietechnik und Thermodynamik der TU Wien. Bei der Modernisierung wurde die Messtechnik erneuert, und eine neue Leistungsbremse angeschlossen, was jedoch nur dokumentiert wurde, und nicht Teil der Arbeit ist. Weiters wurde ein Betriebsmanual erstellt, mit dem die Maschine sicher betrieben werden kann.The thesis is about the upgrade of a stationary gas turbine testbed used by the Vienna Technical University / Institute for Energy Technology and Thermodynamics. The testbed uses a ROVER 1S60 which was developed for low-power applications. In the diploma thesis the renewal of measurement instruments, and the influence on operation of the new eddy current brake are discussed. Further an operation manual is added to the thesis in order to operate the testbed in a correct and safe way.8

Investigations on structure-property relations of (La,Sr)CoO3-[delta] thin film SOFC cathodes

In this thesis (La,Sr)CoO3-d thin films were prepared by PLD and a simple sol-gel route. The electrochemical performance towards oxygen reduction was investigated by impedance spectroscopy. Structural and morphological investigations were performed using XRD, SEM, AFM and TEM.The surface composition was investigated by LEIS and XPS. From that data several structure-property relations were found.The structure and electrochemical performance of (La,Sr)CoO3-d thin-film electrodes prepared by PLD on single crystalline YSZ strongly depends on the deposition temperature of the films. Surprisingly thin films deposited at rather low temperatures (340-510°C) and exhibiting hardly any signal in Bragg-Brentano XRD patterns showed the best electrochemical performance. It was possible to prepare LSC film electrodes with polarization resistances as low as 0.1 Ohmcm² at 600°C.Many electrodes showed a pronounced degradation when operating between 500 and 700°C. Interestingly, the films exhibiting the lowest resistances showed the lowest degradation within a few days of operation. It was further possible to employ a sol-gel route to prepare electrodes with the same performance as the electrodes prepared by PLD. Again it seems that there is a correlation between the degree of crystallinity and the resistance. As the sol-gel thin films are smooth and dense and have no open porosity this extremely fast oxygen reduction cannot be attributed to a strongly increased surface area. It seems to be related to the lower crystallinity or a consequence of the lower crystallinity. The surface composition was investigated by LEIS and XPS. Different results concerning the surface composition of as prepared and heat treated samples deposited at 450°C and 650°C are achieved.10

Synthese und Charakterisierung von Nanostrukturen aus Wolfram- und Molybdänoxiden auf Silizium

Es ist heutzutage notwendiger denn je, Prozesse in der Industrie, Umwelt oder im Alltag genau zu verfolgen. Ein wichtiger Aspekt hierbei ist die Kontrolle der Gasatmosphäre.Die dazu eingesetzten Gassensoren bestehen aus einem beheizten keramischen Material, auf dem ein Metalloxid zwischen zwei Elektroden aufgebracht ist. Falls das Oxid in Kontakt mit einem Gas kommt, diffundiert dieses in die Schicht und ändert somit die elektrische Leitfähigkeit. Die bis jetzt erhältlichen Gassensoren haben jedoch einige Nachteile. Sie sind oft zu unspezifisch, sie altern oder haben eine zu hohe Nachweisgrenze. Daher sind die Anstrengungen entsprechend groß, den Stand der Technik bei Gassensoren zu verbessern.Dies kann über verschiedene Ansätze geschehen. In dieser Arbeit wurde versucht, Molybdän- und Wolframoxid in nanokristalliner Form herzustellen und auf Siliziumplättchen abzuscheiden. Diese könnten dann in weiterer Folge als neue Materialien mit verbesserten Eigenschaften in Gassensoren eingesetzt werden. Die Verbesserung der Sensitivität soll über eine Vergrößerung der Oberfläche erreicht werden. Bei einer größeren Oberfläche können mehr Gasteilchen mit dem Sensor in Kontakt treten, es kommt dadurch schneller zu einem Signal. Die Verbesserung der Selektivität soll über die Anpassung des Sensormaterials an sich erfolgen, da unterschiedliche Materialien auf verschiedene Gase jeweils anders reagieren. Molybdän und Wolfram bilden beide flüchtige Oxide und besitzen die Eigenschaft H2, H2S, CH4, NO2, NH3 oder CO zu detektieren.Es wird die Herstellung von WO3-Nanostrukturen über chemische Transportreaktionen untersucht und diskutiert. Molybdänoxid konnte in Form von länglichen Kristallen mit rechteckigem Querschnitt, sogenannten Nanobelts, hergestellt werden. Wolframoxid wurde hingegen in Form von länglichen Kristallen mit rundem Querschnitt,sogenannten Nanowires, abgeschieden. Eine Modifikation durch Dotierung von Molybdänoxid mit Chrom und Wolfram bzw. eine Mischoxidbildung von Molybdän- und Wolframoxid waren nicht erfolgreich. Darüberhinaus wurde eine erfolgreiche Funktionalisierung der MoO3-Nanobelts mit Wolframoxid-Nanowires durchgeführt.Today there is a great interest in controlling processes in industry, environment or everyday live. Especially the knowledge of the surrounding gas atmosphere is important. The most common gas sensors are metal oxide gas sensors. The fundamental sensing mechanism relies on a change in electrical conductivity due to a reaction of the gas species with the surface of the metal oxide. Often these sensors are not specific enough, the signal is not stable over a long period of time and they are not sensitive enough. These problems cause great efforts to improve existing gas sensing systems. In this work the synthesis of molybdenum- and tungsten oxide nanostructures on silicon-wafers is discussed. These nanostructures should have an improved sensor performance. Due to the huge surface gas molecules can easier interact more easily with the metal oxide and sensitivity is increased. Selectivity should be improved by the modification of the metal oxide. The synthesis of tungsten oxide nanowires is carried out by chemical transport reactions. Molybdenum oxide nanobelts are synthesised by a chemical vapour deposition. A doping of molybdenum oxide with chromium and tungsten and a functionalisation with tungsten oxide has been carried out. With molybdenum- and tungsten oxide H2, H2S, CH4, NH3 and CO could be detected.<br /