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Complete characterization of the ceramic-based hot-coated coating on the AZ91 magnesium alloy
Plevová, Kateřina ; Doskočil, Leoš (referee) ; Wasserbauer, Jaromír (advisor)
The diploma thesis is focused on the study of the thermal sprayed coating consisting of the NiCrAlY alloy bond layer and the partially stabilized zirconium oxide (8YSZ) top layer on the AZ91 magnesium alloy. The theoretical part deals with the structure of the alloy AZ91, NiCrAlY and partially stabilized zirconia. Furthermore, the methods of thermal spraying and the function and properties of thermal barrier coatings are summarized. The experimental part deals with the characterization of the thermal sprayed coating and the AZ91 alloy in terms of elemental, structural and phase composition. Optical and electron microscopy, EDS and XRD analysis were used for characterization. Electrochemical properties were investigated in~3.5% sodium chloride solution by potentiodynamic polarization. The mechanical properties (hardness, coefficient of friction) of the substrate and coating were measured using a hardness tester and tribological tests.
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Boundary Conditions in the Roll Gap during Hot and Cold Rolling
Luks, Tomáš ; Pernis,, Rudolf (referee) ; Hajduk, Daniel (referee) ; Horský, Jaroslav (advisor)
Boundary conditions in the roll gap play an important role in modelling of rolling processes. In the roll gap we can observe the following: changes of rolling pressure, changes of relative velocity, influences of oxides and lubrication, etc. When taking into account all conditions mentioned above the determination of the boundary conditions is not trivial and extensive measurements are necessary. Therefore, this thesis is dealing with design of temperature and force sensors specified for the determination of friction coefficient and heat transfer coefficient in contact. The temperature sensor with an installed thermocouple measures subsurface temperature for a given depth; and then the inverse heat conduction task is used to compute temperature and heat flux on the surface. Several temperature sensors were designed and used for measuring in pilot mill and industrial rolling mill as well. The thermal responses of different sensors were compared in the numerical simulations. The inverse calculations were tested for various rolling conditions. A durability of the sensors was also studied in industrial rolling conditions. The contact stresses in the roll gap were measured by a pin, which was in direct contact with the rolled material. The forces on the top of the pin were measured by a three-axes piezoelectric force transducer and recalculated to the contact stress and friction coefficient. The sensor was implemented in a work roll and tested when rolling aluminium and steel slab for different rolling conditions. The results were compared with the integrative force sensor ROLLSURF.
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Dependance of pavement surface skid resistance on aggregate polishing and traffic loading
Dašková, Jaroslava ; Čelko,, Ján (referee) ; Šachl,, Jindřich (referee) ; Vojtěšek, Antonín (referee) ; Kudrna, Jan (advisor)
Road safety is a complex problem. It is influenced mainly by the driver, the vehicle and the road surface. This thesis is focused on the road surface properties and especially skid resistance that directly affect the braking distance and keeping the vehicle in the horizontal curves and thus traffic accidents. The thesis deals with the durability of pavement surface skid resistance, the type of pavement layers and aggregate polishing used in wearing course. The aim of this thesis was to develop the methodology for improvement of road surfaces skid resistance durability and implementation of functional test for their assessment.
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Pavement skid resistance and Skid Resistance Index
Nekulová, Pavla ; Šachlová, Zora (referee) ; Kudrna, Jan (advisor)
This diploma thesis deals with the relation between the longitudinal friction coefficient dependence on measuring speed and the value of road surface macrotexture MPD. Results of longitudinal friction coefficient and value of MPD measurement on 73 sections are included in this thesis. The results were compared by regression analysis and its outcome was used for determination of formula that enable calculation of longitudinal friction coefficient for any operating speed when longitudinal friction coefficient for 60 km/h and value of macrotexture are known. The evaluation scale for skid resistance index (SRI) was also determined in this thesis. It could be used for evaluation of skid resistance independently of the type of device used for friction coefficient measurement.
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Temperature processes at dry friction
Pešek, Luděk ; Půst, Ladislav ; Cibulka, Jan ; Bula, Vítězslav
Application of dry friction damping contact is very often used for damping of turbine blades vibration. This problem is intensively studied in our Institute for several years, but the deficiency of knowledge of special material’s friction characteristics introduces serious uncertainty into the results of research. Therefore laboratory experimental equipment has been designed and realized. Results of the first set of measurement is presented and discussed. Friction double of steel blade material and overlay of tungsten carbide was investigated at various thrust forces and frequencies of relative motion at the simultaneous measurement of temperatures in tree points near the friction surface. Increase of temperature after 25 s of friction run, friction coefficient, friction force, dissipated energy in one cycle, during 1 s, entire energy during the friction run, lost power, and energy for 1oC temperature increase at various conditions were ascertained.
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Tribologické chovaní tvrdých uhlíkových kompozitních vrstev
Fořt, Tomáš ; Grossman, Jan ; Sobota, Jaroslav ; Vítů, T. ; Novák, R.
Carbon hard composite coatings were exposed to dynamical load and high temperature pin-on-disc CSM Tribometer. To evaluate the impact resistance of thin hard composite coating in dynamic loading wear applications an impact test was used. The sliding tests in air were carried out in the range from room temperature to 500 °C with controlled relative humidity. Hardness, elastic modulus and fracture toughness of deposited coatings were studied by indentation technique using Fisherscope H100 tester.
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Properties of thermo-visco-elastic material 42-809 for manufacturing of vibrodamping elements – 3.part
Svoboda, Jaroslav ; Pešek, Luděk ; Frölich, V. ; Klášterka, Petr
In the report the results of rubber elements properties made of thermo-visco-elastic material 42-809 at low temperatures are summariesed. The tests were performed by a loading fatigue machine INSTRON 8502 in a climate chamber. For improving an accuracy of measurement the test machine was equipped with a lesser force transduser Rumburk with a range up to 40kN. The report includes results of static and dynamic characteristics in temperature range 0 ÷ -50°C, measurement of residual deformations, relaxation time and evaluation of a cyclic loading influence to shapes of static characteristics of the rubber. Furthermore the results of rubber element life time and evaluation of friction behaviour at lower temperatures are presented. The limit lines for 10% of residual deformations are drawn here, too.
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Flow resistance of simple 2D bodies in wide range of Reynolds numbers
Hoření, Bohumír ; Chára, Zdeněk
Paper presents results of numerical simulation of flow resistance of selected 2D bodies (flat plate, cylinder and cylinder of square cross section) with help of program Fluent 6 for Reynolds numbers in the range Re=0.5 - 5000000 and the simulations are compared with available experimental data. The aim of the paper was to determine regions where the numerical calculations could give reasonably results.
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