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1.
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: 1097; Downloads: 59
URL Link to full text

2.
Computational approach to contact fatigue damage initiation analysis of gear teeth flanks
Matjaž Šraml, Jože Flašker, 2006, original scientific article

Abstract: 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.
Keywords: machine elements, fracture mechanics, gears, contact fatigue, crack initiation, numerical modelling, teeth flanks
Published: 30.05.2012; Views: 1603; Downloads: 58
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3.
Pitting formation due to surface and subsurface initiated fatigue crack growth in contacting mechanical elements
Gorazd Fajdiga, Srečko Glodež, Janez Kramar, 2007, original scientific article

Abstract: 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.
Keywords: fracture mechnaics, machine elements, gears, contact fatigue, pitting, subsurface crack initiation, computational analysis
Published: 31.05.2012; Views: 1301; Downloads: 72
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4.
Numerical analysis of the crack growth in a high loaded bolt connection
Marko Knez, Srečko Glodež, Janez Kramberger, 2007, original scientific article

Abstract: The paper deals with the research on the crack growth in a bolt connection of a lug for crane counter weight bars. Counter weight bars are structural elements subjected to very heavy loads and therefore need special attention. The main purpose of this research is to determine the number of load cycles required for a crack to propagate from initial to criticakl crack length, whenthe final failure can be expected to occur. All required material parameters and experimental results were determined in our previous research. The influence of the initial crack siye upon the remaining life of the lug is reserched numericallu by means of FE analysis and analytically by use of the corrected analystical model.
Keywords: fracture mechanics, cyclic loading, fatigue crack growth, service life prediction, numerical analysis, bolt connection
Published: 31.05.2012; Views: 1495; Downloads: 64
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5.
Crack identification in gear tooth root using adaptive analysis
Aleš Belšak, Jože Flašker, 2007, original scientific article

Abstract: 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.
Keywords: machine elements, gears, fatigue crack, fault detection, vibrations, adaptive signal analysis, engineering diagnostics
Published: 31.05.2012; Views: 1196; Downloads: 51
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6.
Microcrack initiation and growth in heat-risistant 15Kh2MFA steel under cyclic loading
P. Yasniy, V.B. Hlado, V. Hutsaylyuk, Tomaž Vuherer, 2005, original scientific article

Abstract: This paper presents the results of investigation of a nuclear reactor pressurevessel steel 15Kh2MFA of two strength levels under cyclic loading. Themechanism of microcrack formation on the surface and in the bulk of 15Kh2MFA steel under cyclic deformation was investigated. Analysis of the specimen surfaces has shown that microcracks are caused by cyclic sliding in grains most favourably oriented with respect to the direction of the maximum shear stresses. Transmission electron microscope investigations show that microcracks in the material inside the grains are formed mainly along the band-type dislocation structure parallel to the dislocation subboundary. During cyclic deformation, the dislocation density on the subboundaries increases, in the local areas the dislocation density becomes limiting and it reaches the plasticity limit and causes microcrack formation. The interrelation of the average length of microcracks and their surface density with the energy density of inelastic deformation has been found.
Keywords: material testing, nuclear reactor, pressure vessel, cyclic loading, cyclic deformation, dislocation structure, fatigue crack growth, TEM, fracture mechanics
Published: 01.06.2012; Views: 1008; Downloads: 18
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7.
Effect of residual stresses on the fatigue crack propagation in welded joints
Nenad Gubeljak, Jožef Predan, Reinhard Pippan, Maks Oblak, 2005, original scientific article

Abstract: The effect of residual stress on the fatigue crack growth was investigated forcyclic tension. Three-point bend specimens were used with through thicknessnotches at the center line of the welded joint. The experiments were performed for different load amplitudes and load ratios under conditions of small-scale yielding. The influence of the residual stresses on fatigue crack growth was estimated by experimentally observed fatigue crack growth rate and measurement of residual stresses at the surface of specimen. This paper describes an approach taken in two models to estimate the residual stress effect on fatigue crack propagation and to predict remaining service life of awelded structure.
Keywords: fracture mechnaics, fatigue crack, crack growth, residual stresses, fatigue crack growh rate, X-ray
Published: 01.06.2012; Views: 1187; Downloads: 58
URL Link to full text

8.
Numerical calculation of bending fatigue life of thin-rim spur gears
Janez Kramberger, Matjaž Šraml, Iztok Potrč, Jože Flašker, 2004, original scientific article

Abstract: Mechanical elements subjected to cyclic loading have to be designed against fatigue. The main goal of the presented analysis was to determine the the bending fatigue life prediction of thin rim spur gears. The service life is divided into the initiation phase of the damage accumulation and the crack growth, resprcitively. The analysis has been performed usig FEM and BEM. The continuum mechanics approach is used for the prediction of the fatigue life initiation phase, where the basic fatigue material parameters are taken into account. The evaluation of the structure remaining life with initial crack the linear-elastic fracture mechanics LEFM principles are applied.
Keywords: machine elements, lineaar elastic fracture mechanics, fatigue, bending, initial crack, service life
Published: 01.06.2012; Views: 1665; Downloads: 66
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9.
The influence of different parameters on surface pitting of contacting mechanical elements
Gorazd Fajdiga, Jože Flašker, Srečko Glodež, 2004, original scientific article

Abstract: 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.
Keywords: machine elements, gears, contact problems, pitting, fatigue crack growth, simulation, model
Published: 01.06.2012; Views: 1129; Downloads: 67
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10.
Evaluation of the service life of gears in regrad to surface pitting
Srečko Glodež, Boris Aberšek, Jože Flašker, Zoran Ren, 2004, original scientific article

Abstract: 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.
Keywords: machine elements, gears, pitting, fatigue, short crack growth, numerical analysis, service life
Published: 01.06.2012; Views: 1429; Downloads: 14
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