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1.
Analysis of noise sources produced by faulty small gear units
Aleš Belšak, Jurij Prezelj, 2007, izvirni znanstveni članek

Opis: Noise source vizualization represents an important tool in the field of technical acoustics. There are many different techniques of noise source visualization. Most of them, however, are intended for a specific noise source in a specific type of acoustic environment. Consequently, a certain visualization method can be used only for certain types of noise sources in a specific acoustic environment and in a restricted frequency area. This paper presents a new visualization method of complex noise sources on the basis of the use of an acoustic camera. A new algorithm has been used, which makes it possible to visualize all types of different complex noise sources. Monopole, dipole or quadropole noise sources can be observed simultaneously. It is possible to track a moving noise source by means of an acoustic camera. In addition to that it is possible to observe various transient acoustical phenomena. Through the use in diagnostics, it is possible to define, by means of noise, the condition of mechanical systems at an advance level.
Ključne besede: gears, failure, noise sources, visualization of noise sources, sound, acoustic analysis, acoustic camera, signal analysis, acoustic image, measurements
Objavljeno: 31.05.2012; Ogledov: 983; Prenosov: 24
URL Povezava na celotno besedilo

2.
Computational approach to contact fatigue damage initiation analysis of gear teeth flanks
Matjaž Šraml, Jože Flašker, 2006, izvirni znanstveni članek

Opis: The paper describes a general computational model for the simulation of contact fatigue-damage initiation in the contact area of meshing gears. The model considers the continuum mechanics approach, where the use of homogenous and elastic material is assumed. The stress field in the contact area and the relationship between the cyclic contact loading conditions and observed contact points on the tooth flank are simulated with moving Hertzian contact pressure in the framework of the finite element method analysis. An equivalentmodel of Hertzian contact between two cylinders is used for evaluating contact conditions at the major point of contact of meshing gears. For the purpose of fatigue-damage analysis, the model, which is used for prediction of the number of loading cycles required for initial fatigue damageto appear, is based on the Coffin-Manson relationship between deformations and loading cycles. On the basis of computational results, and with consideration of some particular geometrical and material parameters, theinitiation life of contacting spur gears in regard to contact fatigue damage can be estimated.
Ključne besede: machine elements, fracture mechanics, gears, contact fatigue, crack initiation, numerical modelling, teeth flanks
Objavljeno: 30.05.2012; Ogledov: 1541; Prenosov: 49
URL Povezava na celotno besedilo

3.
Pitting formation due to surface and subsurface initiated fatigue crack growth in contacting mechanical elements
Gorazd Fajdiga, Srečko Glodež, Janez Kramar, 2007, izvirni znanstveni članek

Opis: A computational model for simulation of surface and subsurface initiated fatigue crack growth due to contact loading is presented. The model is based on fracture mechanics theory where the required materials properties are obtained from common fatigue tests. For computational simulations an equivalent model of two contacting cylinders is used instead of simulating theactual contact of mechanical elements. The discretised model with the initial crack on or under the surface is then subjected to normal contact pressure, which takes into account the EHD-lubrication conditions, and tangential loading due to friction between contacting surfaces. The model considers also the moving contact of mechanical elements and for the surface initiated crack also the fluid trapped in the crack. The virtual crack extension method, implemented in the finite element method is then used for simulating the fatigue crack growth from the initial crack up to the formationof the surface pit. The numerical results correspond well with available experimental data. The described model can be used for simulation ofpitting phenomenon of contacting mechanical elements like gears, bearings, wheels, etc.
Ključne besede: fracture mechnaics, machine elements, gears, contact fatigue, pitting, subsurface crack initiation, computational analysis
Objavljeno: 31.05.2012; Ogledov: 1248; Prenosov: 64
URL Povezava na celotno besedilo

4.
Crack identification in gear tooth root using adaptive analysis
Aleš Belšak, Jože Flašker, 2007, izvirni znanstveni članek

Opis: Problems concerning gear unit operation can result from various typical damages and faults. A crack in the tooth root, which often leads to failure in gear unit operation, is the most undesirable damage caused to gear units. This article deals with fault analyses of gear units with real damages. A laboratory test plant has been prepared. It has been possible to identify certain damages by monitoring vibrations. In concern to a fatigue crack in the tooth root significant changes in tooth stiffness are more expressed. When other faults are present, other dynamic parameters prevail. Signal analysis has been performed also in concern to a non-stationary signal, using the adaptive transformation to signal analysis.
Ključne besede: machine elements, gears, fatigue crack, fault detection, vibrations, adaptive signal analysis, engineering diagnostics
Objavljeno: 31.05.2012; Ogledov: 1148; Prenosov: 43
URL Povezava na celotno besedilo

5.
Analysis of vibrations and noise to determine the condition of gear units
Aleš Belšak, Jurij Prezelj, 2011, samostojni znanstveni sestavek ali poglavje v monografski publikaciji

Opis: The main goal of maintenance is to maintain the characteristics of a technical system at the most favourable or still acceptable level. Maintenance costs can be reduced, operation can become more reliable and the frequency and complexity of damages can be reduced. To evaluate the condition of a technical system, it is necessary to collect precise data, and the to analyse, compare and process this data properly. Gear units are the most frequent machine parts or couplings. They consist of a housing, toothed wheels, bearings and a lubricating system and are of various types and sizes. Durable damages in gear units are often a resulta of the following factors: geometrical deviations or unbalanced component parts, material fatigue, which is a result of engagement of a gear pair, or damages caused to roller bearings. To monitor the condition of mechanical systems, methods for measuring vibrations and noise are usually used; data about a gear unit can be acquired in this way. Afterwards certain tools are used to analyse the data. Features that denote the presence of damages and faults are identified in this way.
Ključne besede: vibrations, noise source identification, maintenance, gears
Objavljeno: 01.06.2012; Ogledov: 943; Prenosov: 44
URL Povezava na celotno besedilo

6.
Review of mathematical and experimental models for determination of service life of gears
Boris Aberšek, Jože Flašker, Srečko Glodež, 2004, izvirni znanstveni članek

Opis: To confirm mathematical models for the determination of service life of gears we developed different nonstandard test pieces and used a combination of mixed experimental methods on them. The aim of these combinations was to obtain as complete information as possible about the individual influences and to detrmine the interaction between different fracture mechanics magnitudes. In this way we confirmed the models as a whole and also determined some physical interpretations in models. With this we were able to ensure that the presented model is not purely a mathematical model.
Ključne besede: machine elements, gears, service life, testing, experimental methods
Objavljeno: 01.06.2012; Ogledov: 1016; Prenosov: 46
URL Povezava na celotno besedilo

7.
The influence of different parameters on surface pitting of contacting mechanical elements
Gorazd Fajdiga, Jože Flašker, Srečko Glodež, 2004, izvirni znanstveni članek

Opis: The paper describes a general computational model for simulation of surface pitting of mechanical elements subjected to contact loading conditions. In the model it is assumed that the initial crack of length 0.015 mm is initiated at the contacting surfaces due to previously thermal, mechanical treatment of the material or running in process. The discretised model with the initial crack is then subjected to normal contact pressure, which takes into account the EHD lubrication conditions and tangential loading due to friction between contacting surfaces. The model accounts also for the influence of fluid trapped in the crack on crack prppagation. The virtual crack extension VCE method within FEM analysis is then used for 2 dimensional simulation of fatigue crack propagation from the initial crack up to the formation of the surface pit. The pit shapes and relationships between the stress intensity factor and crack length are determined for various combinations of contacting surface curvatures and loadings. The comparison of computational and available experimental results shows that the proposed model reliably simulates the surface fatigue crack growth under contact loading and can be used for computational predictions of surface pitting for various contacting mechanical elements.
Ključne besede: machine elements, gears, contact problems, pitting, fatigue crack growth, simulation, model
Objavljeno: 01.06.2012; Ogledov: 1078; Prenosov: 60
URL Povezava na celotno besedilo

8.
Evaluation of the service life of gears in regrad to surface pitting
Srečko Glodež, Boris Aberšek, Jože Flašker, Zoran Ren, 2004, izvirni znanstveni članek

Opis: A computational model for determining the service life of gear teeth flanks in regard to surface pitting is presented. The model considers the material fatigue process leading to pitting, i.e. the conditions required for the short fatigue crack propagation originating from the initial crack in a single material grain. In view of small crack lengths observed in surface pitting, the simulation takes into account the short crack growth theory. The stress field in the contact area and the required functional relationship between thestress intensity factor and the crack length are determined by the finite element method. An equivalent model of two contacting cylinders is used for numerical simulations of crack propagation in the contact area. On the basis of numerical results, and with consideration of some particular material parameters, the probable service life period of contacting surfaces is estimated for surface curvatures and loadings that are most commonly encountered in engineering practice.
Ključne besede: machine elements, gears, pitting, fatigue, short crack growth, numerical analysis, service life
Objavljeno: 01.06.2012; Ogledov: 1381; Prenosov: 14
URL Povezava na celotno besedilo

9.
Computational model for the analysis of bending fatigue in gears
Janez Kramberger, Matjaž Šraml, Srečko Glodež, Jože Flašker, Iztok Potrč, 2004, izvirni znanstveni članek

Opis: A computational model for the determination of service life of gears with regard to bending fatigue in a gear tooth root is presented. The fatigue process leading to tooth breakage is divided into crack initiation (Ni) and crack propagation (Np) periods, where the complete service life is defined as N = Ni + Np. The strain-life method in the framework of the FEM method has been used to determine the number of stress cycles Ni required for fatigue crack initiation. Gear tooth crack propagation was simulated using a FEM method based computer program which uses principles of linear elastic fracture mechanics. The Paris equation is then used for the further simulation of the fatigue crack growth. The presented model is used to determine the service life of a real spur gear made from through-hardened steel 42CrMo4.
Ključne besede: machine elements, gears, bending fatigue, service life, fatigue crack initiation, fatigue crack propagation, computational simulations, numerical modelling, fracture mechanics
Objavljeno: 01.06.2012; Ogledov: 2140; Prenosov: 52
URL Povezava na celotno besedilo

10.
Numerical procedure for predicting the rolling contact fatigue crack initiation
Matjaž Šraml, Jože Flašker, Iztok Potrč, 2003, izvirni znanstveni članek

Opis: A computational numerical model for contact fatigue damage analysis of mechanical elements is presented in this paper. The computational approach is based on continuum mechanics, where a homogenous and elastic material model isassumed in the framework of the finite element method analysis. Cyclic contact loading conditions are simulated with moving Hertzian contact pressure. The time-depending loading cycles are defined for each observed material point on and under the contact area. Furthermore, the influence of friction upon rolling-sliding contact loading cycles is analysed in detail, using Coulombćs friction law. The model for prediction of the number of loading cycles, required for initial fatigue damages to appear, is based on Coffin-Manson relations between deformations and loading cycles, and includes characteristic material fatigue parameters. As a general example, the model isused to analyse a fundamental contact problem of a cylinder and flat surface, which is usually a substitutional model for analysing real mechanicalproblems. However, the results concerning the identification of critical material points and the number of loading cycles, required for initial fatigue damages to appear at those points, are the main purpose of thepresented study.
Ključne besede: machine elements, gears, contact problems, contact fatigue, crack initiation, numerical modelling
Objavljeno: 01.06.2012; Ogledov: 1035; Prenosov: 35
URL Povezava na celotno besedilo

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