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UHMWPE failure in knee joint component
Franta, L. ; Jeníková, Z. ; Pražák, Josef ; Suchánek, J.
A simulation of realistic tribologic conditions in tests “in vitro”contributes significantly to the research in the field of joint replacements. Motion under low relative velocities of friction surfaces of knee joint replacements is studied. The simulator enabled combination of rolling and sliding motion of replacement components. During the experiment, numerous debris of UHMWPE component ares produced and the friction surface is irreversibly changed. Initially, the irregularities of tibial component are smoothed. Consequently, large amount of UHMWPE debris is released. Specimens were loaded for 15.105 cycles with dry or distilled water lubrication. The surface changes of specimens were evaluated.
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Přechodové teplotní pole v komoře pro měření povrchového napětí podchlazených kapalin
Hrubý, Jan ; Müller, M. ; Richtr, K. ; Mareš, R.
Results of mathematical modeling of the transient temperature field in a new chamber developed to measure surface tension of supercooled liquids are presented. The chamber is designed to enable a very fast (within 0.1 s) formation of a homogeneous temperature field (within 0.02 K) after a temperature jump of 60 K. The interior of the chamber of dimensions 20x16x32 mm is filled with dry nitrogen surrounding the measuring capillary and thermometers (very fine thermocouples and RTD’s). The temperature jump is generated by switching the flow direction of the nitrogen serving as a heat transmitting fluid. To reduce the thermal boundary layer near the bottom and ceiling walls, they are made permeable and some gas is sucked out. The flow in the chamber is laminar. We compute the temperature field analytically and numerically, using the commercial software Fluent. The results indicate that the design objectives of the experimental device were met.
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Aerodynamická optimalizace profilů pro větroně
Popelka, Lukáš ; Matějka, M.
The article describes procedure of sailplane airfoil optimization with use of available numerical and experimental methods. Comments are given on calculation of boundary layer transition, integral parameters, measurement of maximum lift coefficient, visualization and flow control.
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Self-excited oscillation of the thin-walled elastic tubes
Chlup, Hynek ; Maršík, František ; Konvičková, S.
The simulation of the fluid flow through elastic pipes has many applications in a blood flow through human vessels – investigation of such phenomena as an atherosclerosis generation in artery walls, the Korotkoff's sounds generation or modeling of vascular mechanical substitutes (the so called "stents") and is therefore widely studied. Aim task is to solve the blood flow through the elastic tubes analytically, numerically and experimentally and to analyze the relation of the mechanical properties of the blood and of the vessel wall and flow instabilities, all focused on biomechanics of the cardio-vascular system. The analysis shows that frequency of self-excited oscillations increases with the decrease of arterial compliance.
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Experimentální měření pulzní vlny v elastické trubici
Chlup, Hynek ; Macková, H. ; Žitný, R. ; Konvičková, S.
The pulse wave velocity (PWV) in blood vessels is one of the important hemodynamical parameters for detection of artery health condition. In our laboratory, the PWV in elastic tubes and arteries is measured in vitro. The method is based on optical measurements of displacement of the pulsating tube wall. A high frame rate camera was used. The obtained data were evaluated by several methods and compared. The measured pulse wave velocities were in the same order of magnitude as values based on theoretical calculations and published physiological data.
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The Effect of Overloading of Pipes on their Fracture Toughness in Relation to the Strength Grade of Steel
Šperl, Martin ; Gajdoš, Lubomír
The present experimental results showed a very positive effect of a controlled overloading of a pipeline on its fracture toughness. These results have been referred to steels of the class L360MB and L415MB. However, more recent results obtained on L450MB steel indicated that the positive effect of oveloading is reduced as the strength properties of steels are increased. It follows from this that the final technological operation of overloading of pipes made from steels of an increased strength could be let out from the pipe manufacture scheme. The paper presents experimental results which prove by evidence a decreasing positive effect of overloading on the fracture toughness of steels of high strength properties.
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Contribution to Experimental Research of Vibro-Acoustics of Railway wheels with add-on Dampers
Pešek, Luděk ; Vaněk, František ; Veselý, Jan ; Cibulka, Jan ; Boháč, T.
In the contribution a method of measurement and dynamic analysis of the recent operational tests of the monobloc wheel with/without damping elements is presented. On the basis of time-frequency analysis of operational vibration and experimental modal analysis of the wheel its dynamic behavior is described. The vibro-acoustic coupling is analyzed from the comparisons of vibration and sound pressure spectrograms. At passing the curve, the formation and modal-frequency composition of squealing noise is observed and there are identified vibrational modes that mostly contribute to noise emission into surrounding. For quantitative comparison of individual wheel solutions the third octave analysis is used.
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Calculation of the Ceramics Material Parameters from the Testing Destructions of the Heads
Fuis, Vladimír ; Návrat, Tomáš ; Hlavoň, Pavel
This paper deals with increasing of the computation modelling level of the reliability problem of ceramic heads of total hip joint endoprostheses. The solution to this problem was invoked by recent more frequent failures of these heads in clinical practice. Results of computational and experimental modelling have shown a substantial influence of shape deviations in the conical connection between stem and head on the initiation of ceramic head fractures. The fracture probability was evaluated step by step for various macroscopic shape deviations in the conical connection and then for microscopic shape deviations superposed on the macroscopic deviations.
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Assessment of the sensor temperature in HWA
Antoš, Pavel
One of the key parameters in hot-wire anemometry is the temperature of the sensor. The temperature is set on CTA via the resistivity of the hot sensor. Several probes were tested using a variable temperature oil bath. Dependence of the resistivity on the temperature and means of its estimation are the subjects of the paper.
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