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Effect of surface roughness on lubrication of plain bearings
Vaněk, Tomáš ; Hartl, Martin (referee) ; Šperka, Petr (advisor)
This work investigates the influence of surface roughness on the lubrication of axial hydrodynamic bearings with convergent wedge gaps. It focuses on situations where operational conditions allow for full separation of surfaces by the lubricating film, as well as the transition to mixed lubrication. The aim is to understand the impact of surface roughness on the hydrodynamic lubrication process and whether their proper selection can affect the friction and load-carrying capacity of the bearing. Experimental measurements are used to determine the influence of parameters, where the thickness of the lubricating film is captured through fluorescence microscopy, along with the friction force at the contact between the pin and the test sample. The samples form a wedge gap with a rotating saphire disk, and the investigated surface roughness parameters include orientation, height Sq, and skewness Ssk (i.e., the relative ratio of depressions and protrusions). According to the obtained results, the orientation, height, and shape of roughness are key factors influencing hydrodynamic lubrication. However, the orientation alone does not determine the contact behavior, and additional roughness parameters must be considered for a complete understanding of the phenomenon. Increasing surface roughness negatively affects lubrication, but the proper combination of Ssk and orientation can minimize this effect. This work represents one of the first experimental measurements examining the influence of surface roughness on hydrodynamic lubrication. The findings have applications not only in plain bearings, but also in other components such as wet couplings or other sliding interfaces using hydrodynamic lubrication.
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Experimental study of friction and lubrication in THR
Urban, Filip ; Čermák, Jan (referee) ; Vrbka, Martin (advisor)
This work analyzes problems of friction and lubrication of total hip replacement (THR). At first, experimental study of friction coefficient under various conditions was conducted using hip joint simulator based on principle of pendulum. After that, lubrication film development was observed, using colorimetric interferometry with head from THR and glass cup with respect of geometry and clearance to cups made originally for THR. With respect to research study [25] it was found that increasing contact conformity leads to increased film thickness. Also protein adsorption on articulating surfaces was observed. Thanks to adsorption 80 nm film thickness was measured even if relative surface speed was zero. Furthermore protein aggregation was observed on the border of contact zone, similar aggregations were observed by Myant et al. [29] or Vrbka et al. [25]. These aggregations are formed when lubricant is under shear stress and it can positively affect film thickness. If the relative motion of articulating surfaces is not sufficient, the protein layer can`t be refreshed enough and film thickness start decreasing. Coefficient of friction 0,13 was measured when lubricating film development was observed. Close to this value are material combinations metal on polyethylene and metal on metal.
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Mapping of lubricating film thickness of human big joints replacements
Bosák, Dalibor ; Hartl, Martin (referee) ; Vrbka, Martin (advisor)
This master’s thesis describes mechanism of lubricating film forming and its thickness in contact of a metal hip joint ball and a glass disc with chromium layer with presence of bovine serum as substitute of synovial fluid occured in a natural joint. Lubricating film thickness is evaluated by a thin film colorimetric interferometry, results are ploted at graphs representing dependence of lubricating film thickness on experiment duration or on mutual speed of articulating surfaces. There is described the influence of concentration of bovine serum and different kinematic conditions on lubricating film forming. From observed interferograms is apparent the adsorption of proteins to glass disc and femoral head surfaces, denaturation and formation of protein aggregations affecting the residual lubricating film thickness.
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Experimental study of friction and lubrication in THR
Urban, Filip ; Čermák, Jan (referee) ; Vrbka, Martin (advisor)
This work analyzes problems of friction and lubrication of total hip replacement (THR). At first, experimental study of friction coefficient under various conditions was conducted using hip joint simulator based on principle of pendulum. After that, lubrication film development was observed, using colorimetric interferometry with head from THR and glass cup with respect of geometry and clearance to cups made originally for THR. With respect to research study [25] it was found that increasing contact conformity leads to increased film thickness. Also protein adsorption on articulating surfaces was observed. Thanks to adsorption 80 nm film thickness was measured even if relative surface speed was zero. Furthermore protein aggregation was observed on the border of contact zone, similar aggregations were observed by Myant et al. [29] or Vrbka et al. [25]. These aggregations are formed when lubricant is under shear stress and it can positively affect film thickness. If the relative motion of articulating surfaces is not sufficient, the protein layer can`t be refreshed enough and film thickness start decreasing. Coefficient of friction 0,13 was measured when lubricating film development was observed. Close to this value are material combinations metal on polyethylene and metal on metal.
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Mapping of lubricating film thickness of human big joints replacements
Bosák, Dalibor ; Hartl, Martin (referee) ; Vrbka, Martin (advisor)
This master’s thesis describes mechanism of lubricating film forming and its thickness in contact of a metal hip joint ball and a glass disc with chromium layer with presence of bovine serum as substitute of synovial fluid occured in a natural joint. Lubricating film thickness is evaluated by a thin film colorimetric interferometry, results are ploted at graphs representing dependence of lubricating film thickness on experiment duration or on mutual speed of articulating surfaces. There is described the influence of concentration of bovine serum and different kinematic conditions on lubricating film forming. From observed interferograms is apparent the adsorption of proteins to glass disc and femoral head surfaces, denaturation and formation of protein aggregations affecting the residual lubricating film thickness.
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