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Measurement of friction coefficient between damping wire and groove
Šnábl, Pavel ; Pešek, Luděk ; Bula, Vítězslav ; Běhálek, V. ; Boháč, T. ; Tašek, H.
Damping wire is being used on railway wheels for noise suppression. It is inserted into a groove of the wheel and dry friction damping reduces vibrations and thus the noise transmitted by the wheel. For increase of durability of the wire, surface treatment of the groove and the ring must be applied to prevent corrosion. Three combinations of diferent surface treatments were studied during reciprocating motion in a set of measurements with diferent frequencies and normal forces to evaluate friction coeficient. Then, those measurements were repeated after a long-time run to evaluate the change of friction coeficient after the wear of the surfaces.
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Vibrational tests and dynamic analysis of friction effect at railway wheel damped by damping ring
Pešek, Luděk ; Půst, Ladislav ; Bula, Vítězslav ; Šnábl, Pavel ; Boháč, T. ; Tašek, H. ; Běhálek, V.
Experimental modal analysis with one (SIMO) and two (MIMO) exciters with the following objectives: (a) to develop a test methodology to evaluate the friction effect of the damping ring on the vibration damping of the wheel, b) to describe changes in the measured dynamic amplitude-frequency and phase-frequency characteristics to the excitation amplitude and to show the non-linear frictional behavior of the circular damping ring in the wheel groove for different natural vibration shapes was carried out in the dynamic laboratory of Bonatrans a.s. on 11-16 June 2019. The proposed methodology and analysis of the measured results in terms of the effect of the friction couplings of the circular wire are described in the report. This work was performed for design of the damping friction ring with variable curvature and optimal distribution of contact pressures in the groove, which is the aim of the DELTA project.\n
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New method of complex modulus estimation of prepressed rubber by the FE model parameter tuning – rubber-damped wheel application
Šulc, Petr ; Pešek, Luděk ; Bula, Vítězslav ; Cibulka, Jan ; Boháč, T. ; Tašek, H.
The main goal of the study was to develop a method for estimation of the frequency dependence of material constants of the pre-pressed hard synthetic rubbers. It was motivated the need to identify material constants, i.e. Young modulus and loss factor, of rubber segments pressed between the disk and the rim of a rubber-damped railway wheel. The rubber segments are pre-pressed about 20% strain level during the production of the wheel. Hard synthetic rubber materials exhibit complex thermalfrequency behavior with nonlinear dependence on static preload. The standard experimental procedures that evaluate the frequency dependence of the material are based on the vibrations of a cantilever beam that consists of a metal and a rubber layer. The new estimation method of the complex modulus of elasticity of rubber is based on the tuning of rubber constants of an FE wheel model according to the results of natural frequencies and mode shapes of the wheel ascertained from the experiment. Numerical FE model of the wheel consisted of the cyclic model of 1/24 sector of the wheel with an angle of 15° and containing one rubber segment and was created in ANSYS 14.5. Damping model of rubber is described by a special case of proportional damping. For calculating eigenvalues of the problem, the Lanczos method was used for the wheel as an undamped system and QR damped method for the damped system. The experimental modal analysis of the rubber-damped wheel pressed on the shaft took place at room temperature in the dynamic laboratory. Modal tests were performed in configuration with an exciter acting first in the axial direction and consequently in the radial direction of the wheel. Responses to the exactions were measured in three directions at 144 points. The identification of eigenvalues and mode shapes of the wheels was made separately for excitations both in radial and in axial direction.
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