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Experimental Study of the Lubricant Film under Starved Conditions
Košťál, David ; Čermák, Jan (referee) ; Dzimko, Marián (referee) ; Ali, Fadi (referee) ; Křupka, Ivan (advisor)
The dissertation thesis deals with an experimental study of an elastohydrodynamic contact under insufficient lubricant supply. Theoretical studies published in this research area focus mainly on the development of theoretical models and there is an insufficient number of experimental studies which validate these models. There are two basic methods of starvation severity control in published theoretical models: by positioning of an inlet meniscus and by setting the thickness of an oil layer in the vicinity of contact inlet. The second method is more suitable when considering a wide range of operating conditions, however it is difficult to ensure experimentally. This thesis presents original experimental results and aims to describe the starvation severity level as a function of the inlet film thickness. Deeper understanding of fundamental processes in starved elastohydrodynamic contacts enables the development of more precise models, better ability of prediction of the starvation and improves the ability to avoid starvation in the early design process of key tribological components.
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Effects of Non-Newtonian Lubricants on Surface Roughness in Point Contacts
Ficza, Ildikó ; Kaneta, Motohiro (referee) ; Poll, Gerhard (referee) ; Hartl, Martin (advisor)
Tato dizertační práce je zaměřena na studium deformace nerovnosti uvnitř elastohydrodynamicky mazaného (EHD) kruhového kontaktu. Práce se zabývá studiem přechodu příčné nerovnosti přes kontaktní oblast, která je modelována pomocí numerických metod. Model dále uvažuje nenewtonské chování maziva. Použitý matematický model se skládá z parciální diferenciální rovnice druhého řádu pro řešení tlaku a integro-diferenciální rovnice pro řešení elastických deformací. Pro řešení tohoto modelu je použitá takzvaná multigrid (vícesíťová) metoda. Práce obsahuje popis matematického modelu EHD kontaktu a aplikované numeriké metody. Výsledky simulací jsou porovnány s experimentálně stanovenýma hodnotama tloušťky mazacího filmu. Deformace nerovnosti uvnitř kontaktní oblasti je studována pro různé provozní podmínky (střední rychlost, poměr proklzu) a různá vlastnosti maziva.
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Study of Elastohydrodynamic Film Formation in Hypoid Gears
Omasta, Milan ; Dobeš, Petr (referee) ; Čermák,, Jan (referee) ; Dzimko, Marián (referee) ; Křupka, Ivan (advisor)
This PhD thesis deals with elastohydrodynamic lubrication (EHL) under the conditions that occur between mated hypoid gear teeth. The aim is to describe experimentally the behaviour of lubricating film and mechanisms of its formation. The focus is mainly placed on clarifying the influence of direction and magnitude of sliding velocity in circular and elliptical contacts. Generally, it is still assumed that the direction of sliding velocity has no effect on the resulting lubricant film. In this study optical interferometry is used to determine distribution of lubricant film thickness. This work includes new and original results which clarify the studied problem. It was found that the direction of sliding velocity affects shape of the film at high speeds. This relates to the effect on heat flow through the contact. The results have an impact on the development of general EHL theory and provide knowledge applicable in film thickness prediction in the design of real tribological nodes.
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In-situ Study of Surface Topography Changes in Elastohydrodynamic Contact
Šperka, Petr ; Dzimko, Marián (referee) ; Návrat, Tomáš (referee) ; Dobeš, Petr (referee) ; Hartl, Martin (advisor)
This dissertation thesis deals with elastohydrodynamic lubrication (EHL) of surfaces with real roughness. Systematic study of surface harmonic components behaviour, during their passage of the EHL contact, by other authors led to retrieval of a uniform principle according which individual harmonic components deform inside the contact. Although the amplitude attenuation model can provide rapid tool for more accurate surface assessment in design process it has not been validated on real surfaces till now. The thesis represents pioneering work on quantitative analysis of real surfaces EHD measurements. It contains original and new results with real and model roughness features that in many cases confirm theoretical expectations. Deeper understanding of surface roughness behaviour inside EHL contact, which is typical for machine parts like bearings, gears, cams etc., can help to improve design process of the components and ultimately enable machines and equipment to work with lower energy requirements and higher durability.
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The effect of surface grooves on point contacts lubrication
Matoušek, Kamil ; Čermák, Jan (referee) ; Šperka, Petr (advisor)
This diploma thesis deals with experimental study of the effect of surface grooves on distribution of lubricant film in elastohydrodynamic lubricated point contact. Lubricant film thickness was measured by ball-on-disc apparatus using an optical interferometry technique - thin film colorimetric interferometry. The effects of groove geometry, lubricant and operating conditions were studied in this diploma thesis. The effects of these variables are evaluated based on newly suggested parameter Rgi (groove influence ratio). Groove influence ratio is defined as an influenced film thickness influenced by groove divided by film thickness for smooth surfaces.
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Suitable lubricants for deep drawing of stainless steel
Mück, Jonáš ; Staněk, Vojtěch (referee) ; Lidmila, Zdeněk (advisor)
The intention of this thesis is the experimental evaluation of different lubricants and their suitability for deep drawing of stainless steel 1.4404. The testing method is based on the friction model at the point of drawing edge and retainers. This model corresponds with a structure of testing fixture. The suitability of every single lubricant for this application has been determined by comparison of the output, which is dependance of the strength on the track with the reference results. The testing has been performed on many different samples provided by various manufacturers. The best result was measured with the oil Kalorex AT 650 S, manufactured by AT Oil, which belongs to the group of environmentally harmful lubricants. Based on the results of this experiment we can conclude that chlorine content significantly increases the lubrication capability especially under high pressure. The modification of preparation geometry which presumes the elimination of certain undesirable disturbances accompnaying the experiemnt has been also proposed.
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Experimental Study of Wheel Flange Lubrication
Frýza, Josef ; Dzimko, Marián (referee) ; Omasta, Milan (advisor)
This diploma thesis deals with the experimental study of the influence of operating conditions on the tribological aspects of the wheel flange and rail gauge contact. The wheel flange contact occurs when the vehicle moves on a curve track and it leads to severe up to catastrophic wear regime. For effective reduction of wear is important to apply a suitable amount of lubricant at appropriate intervals into the contact. The issue in this work comprehensively studies using of three laboratory apparatus and six methods that are theoretically and experimentally compared. Assessed are friction, wear, distribution and film thickness of lubricants for different contact conditions. The resulted amount of lubricant and interval of its application eliminates development of seizure at low consumption of lubricant. The understanding of mechanisms that occur in the wheel-rail contact not only helps to reduce operating costs and improved to energy efficiency of movement of vehicle on a track, but it is the basis for safe, reliable and ecological operation of rail transport.
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Lubricants created by nature
Drobilič, Ivo ; Urban, Filip (referee) ; Nečas, David (advisor)
This bachelor thesis provides an overview of substances which can be considered as the lubricants in its natural environment. The first part of the thesis of focused on lubricants in human body. The substances such as water, blood or synovial fluid are analysed in a detail. The following chapter deals with lubricants in everyday life. As the example, decrease of tyre adhesion in case of rain or longer breaking distance of trains as a consequence of presence of leafs on rails, can be mentioned. The last part, in addition, summarizes the lubricants which are based on natural products.
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Plant oils for industry
Beran, Vojtěch ; Ficza, Ildikó (referee) ; Frýza, Josef (advisor)
This bachelor thesis describes usability of plant oils as liquid greases. The beginning of thesis follow up tribology problems and process of lubrication. The main section describes plant oils from perspective of their chemical composition and its closely related properties. In this thesis, plant oils are compared with another common liquid oils together with the comparison of its properties on specific application. In the conclusion, the thesis deals with summary of plant oils issues and with prospects for the future.
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