| | SLO | ENG | Cookies and privacy

Bigger font | Smaller font

Search the digital library catalog Help

Query: search in
search in
search in
search in
* old and bologna study programme


1 - 7 / 7
First pagePrevious page1Next pageLast page
Influence of different load models on gear crack path shapes and fatigue lives
Srđan Podrug, Damir Jelaska, Srečko Glodež, 2008, original scientific article

Abstract: A computational model for determination of the service life of gears with regard to bending fatigue at gear tooth root is presented. In conventional fatigue models of the gear tooth root, it is usual to approximate actual gear load with a pulsating force acting at the highest point of the single tooth contact. However, in actual gear operation, the magnitude as well as the position of the force changes as the gear rotates. A study to determine the effect of moving gear tooth load on the gear service life is performed. The fatigue process leading to tooth breakage is divided into crack-initiation and crack-propagation period. The critical plane damage model has been used to determine the number of stress cycles required for the fatigue crack initiation. The finite-element method and linear elastic fracture mechanics theories are then used for the further simulation of the fatigue crack growth.
Keywords: crack closure, crack initiation, crack propagation, gear tooth root, moving load
Published: 31.05.2012; Views: 748; Downloads: 61
URL Link to full text

Method for detecting fatigue crack in gears
Aleš Belšak, Jože Flašker, 2006, original scientific article

Abstract: The most undesirable damage that can occur in gear units is crack in the tooth root as it often makes gear unit operation impossible. Monitoring vibrations can be used to detect defects. Time signals are acquired experimentally and afterwards. Different methods can be used to analyse them. The changes in tooth stiffness caused by a fatigue crack in the tooth root are of significance. The dynamic response of a gear unit with a damaged tooth differs from the one of an undamaged tooth. Amplitudes of time signal are, by time-frequency analysis, presented as a function of frequencies in spectrum.
Keywords: gear drives, fatigue failures, crack initiation, crack propagation, vibrations
Published: 31.05.2012; Views: 1098; Downloads: 59
URL Link to full text

Nonlinear vibrational analysis of diesel valve gear
Jurij Avsec, Zdravko Praunseis, Milan Marčič, 2011, original scientific article

Abstract: A valve gear system is currently more or less a classical mechanical system in a majority of diesel engines. In our case, diesel engine durability test was carried out incorporating a conventional valve gear. After the 3000-hour engine test, the manifestations of an intensive wear detected on the exhaust side of the valve gear. The wear of the exhaust cam was particularly intensive right under the top. As evident from dynamical analysis and experimental data of the valve gear the loads are excessive mainly on the exhaust cam. The assessment of the minimum oil film thickness at the top of the exhaust cam does not provide any favorable results. As the largest loads are exerted at the top of the cam, where the highest wear was measured, it is necessary to reduce the normal stresses and improve the lubrication properties. Dynamic valve gear analysis was performed in order to estimate cam wear intensity and to compare the new cam designs with the existing ones. The model of the actual valve gear design can be represented by means of the partial differential equations. We used a vibrational system with three degrees of freedom. Partial differential equations were solved by means of finite differences and Runge-Kutta methods. Vibrational analysis allows studying kinematic and dynamic behavior of the nonlinear spring and nonlinearity of the damping forces in the valve gear system. The presented theory will be applied in the future research works for determining the conditions for chaotic behavior of the valve gear system. The dynamic model of the valve gear was used to analyze the causes of the excessive wear. Since the cam, designed in accordance with the polysine curve, offered too few possibilities for an optimum cam profile, we wanted to manufacture a completely new type of cam with more possibilities for an optimum adjustment. At the same time, we attempted to summarize some findings on the dependence of the cam design on the fuel consumption and valve gear noise. Thereby a new MULTICAM cam was developed. Contrary to the conventional theory of polysine cam, the motion in the MULTICAM cam can be written by means of seven curves. The analysis of Hertz pressures provides more favorable results for the MULTICAM cam profile. By using the new cam profile the Hertz pressures were substantially reduced. The top of the cam is subjected to the lowest loads with the MULTICAM curve shape. In spite of a higher contact force the normal stresses are lower mainly due to the higher radius of cam curvature. Dynamic analysis demonstrates that both newly designed cams exhibit lower stresses at the top of the cam and better lubrication properties, whereas the flow geometrical cross-sections and the other control values remain similar for all three cam versions.
Keywords: disel valve gear vibration, nonlinearity, cam design, valve gear dynamics
Published: 05.06.2012; Views: 1569; Downloads: 21
URL Link to full text

Adaptive wavelet transform method to identify cracks in gears
Aleš Belšak, Jože Flašker, 2010, original scientific article

Abstract: Many damages and faults can cause problems in gear unit operation. A crack in the tooth root is probably the least desirable among them. It often leads to failure of gear unit operation. By monitoring vibrations, it is possible to determine the presence of a crack. Signals are, however, very noisy. This makes it difficult to define properties of individual components. Wavelet analysis is an effective tool for analysing signals and for defining properties. In this paper, a denoising method based on wavelet analysis, which takes prior information about impulse probability density into consideration, is used to identify transient information from vibration signals of a gear unit with a fatigue crack in the tooth root.
Keywords: gear unit, wavelet analysis, wavelet denoising
Published: 26.06.2017; Views: 425; Downloads: 176
.pdf Full text (3,35 MB)
This document has many files! More...

Methods for detecting fatigue cracks in gears
Aleš Belšak, Jože Flašker, 2009, published scientific conference contribution

Abstract: A crack in the tooth root is the least desirable damage caused to gear units and it often causes failure of gear unit operation. For fault analyses presented in this article, gear units with real damages or faults produced on the basis of numerical simulations of real operating conditions are used; tests were carried out in a laboratory test plant. Damages in gear units can be identified by monitoring vibrations. The influences of a crack in a single-stage gear unit on produced vibrations are presented. Significant changes in tooth stiffness are caused by a fatigue crack in the tooth root whereas, in relation to other faults, changes of other dynamic parameters are more expressed. Non-stationary signals are analysed, using the family of Time Frequency Analysis tools, which include Wavelets and Joint Time Frequency Analyses.
Keywords: gear unit, vibrations, tooth root, time frequency analysis tool
Published: 30.06.2017; Views: 283; Downloads: 221
.pdf Full text (705,13 KB)
This document has many files! More...

Designing the gear body structure to control vibration behaviour
Riad Ramadani, 2018, doctoral dissertation

Abstract: This research presents a new approach aiming to reduce gear vibration as well as its weight by modifying the gear body structure. The primary objective was to reduce vibration and noise emission of spur gears. For this purpose, a solid gear body was replaced by a cellular lattice structure, which was expected to raise the torsional elasticity of the gear body. The cellular lattice structure was designed and optimized by FE-based topology optimization software CAESS ProTOp, which is based on strain energy control. For experimental purposes, the optimized gear was produced from Titanium alloy Ti-6Al-4V ELI by using Selective Laser Melting technique. A polymer matrix was added to increase the damping of the structure. In order to test the gears, a new test rig with closed loop was conceived, designed and produced. The test rig is equipped with two gear pairs: with the tested one and with the driving one. The gears have been run and tested at different speeds and torque. The acceleration, strain and sound pressure of a running gear pair was measured. The final processing of the signal was done by a specially developed software based on LabView. By employing the fast Fourier transformation the time signal of acceleration, strain and sound pressure has been converted to the frequency spectrum and time frequency spectrogram. The results obtained by testing the solid and cellular lattice gear body were compared. It was experimentally confirmed that the cellular lattice structure of a gear body and addition of a polymer matrix may significantly reduce the vibration.
Keywords: Gear vibration, cellular lattice structure, topology optimization, test rig
Published: 27.02.2018; Views: 687; Downloads: 98
.pdf Full text (13,76 MB)

Search done in 0.15 sec.
Back to top
Logos of partners University of Maribor University of Ljubljana University of Primorska University of Nova Gorica