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Modelling of surface crack growth under lubricated rolling-sliding contact loading
Boštjan Zafošnik, Zoran Ren, Jože Flašker, Gennady Mishuris, 2005, izvirni znanstveni članek

Opis: The paper describes modelling approach to computational simulation of surface crack growth subjected to lubricated rolling-sliding contact conditions. The model considers the size and orientation of the initial crack, normal and tangential loading due to rolling-sliding contact and the influence of fluid trapped inside the crack by a hydraulic pressure mechanism. The motion of the contact sliding load is simulated with different load cases. The strain energy density (SED) and maximum tangential stress (MTS) crack propagation criteria are modified to account for the influence of internal pressure along the crack surfaces due to trapped fluid. The developed model is used to simulate surface crack growth on a gear tooth flank, which has been also experimentally tested. It is shown that the crack growth path, determined with modified crack propagation criteria, is more accurately predicted than by using the criteria in its classical form.
Ključne besede: fracture mechanics, numerical methods, contact loading, finite element analysis, internal pressure, maximum tangential stress, strain energy density, surface crack growth
Objavljeno: 01.06.2012; Ogledov: 1602; Prenosov: 52
URL Povezava na celotno besedilo

3.
Numerical modelling of crack path in the lubricated rolling-sliding contact problems
Srečko Glodež, Rok Potočnik, Jože Flašker, Boštjan Zafošnik, 2008, izvirni znanstveni članek

Opis: A two-dimensional computational model for simulation of contact fatigue of lubricated rolling-sliding contact problems is presented. In the model it is assumed that the initial crack of length 0.02 mm is initiated at the surface due to previous mechanical or heat treatment of the material as well as a consequence of running process in an early stage of exploitation. The discretised model with the initial crack is then subjected to the normal contact pressure and tangential loading due to friction between the contacting surfaces. The model also considers the moving contact of the contacting surfaces and fluid trapped in the crack. The crack propagation pathis predicted with the MTS and modified MTS criterion, which takes into account the influence of the stress intensity factor KI and KII, T-stress, stress on the crack surface caused by lubricant pressure inside the crack and critical distance ahead the crack tip. The numerical results correspond well with available experimental data.
Objavljeno: 01.06.2012; Ogledov: 841; Prenosov: 43
URL Povezava na celotno besedilo

4.
Investigation of crack propagation scatter in a gear tooth's root
Stanislav Pehan, Janez Kramberger, Jože Flašker, Boštjan Zafošnik, 2008, izvirni znanstveni članek

Opis: This paper describes the problem of determining crack initiation location and its influence on crack propagation in a gear tooth's root. Three different load positions on the gear tooth's flank were considered for this investigation of crack initiation and propagation. A special test device was used for the single tooth test. It can be concluded from the measurements thata crack can be initiated at very different locations in a tooth's root and then propagate along its own paths. A numerical investigation into a crack initiation's position and its influences on its propagation were carried out within the framework of linear fracture mechanics. The influence of a tooth's load position, the geometry of the tooth's root, and the influence of nonparallel load distribution on the tooth's flank were considered when investigating the crack initiation's position. Results show that linear fracture mechanics can be used for determining crack propagation, if better initial conditions for crack initiation are considered.
Ključne besede: fracture mechanics, crack initiation, experimental crack propagation, numerical crack propagation, crack location, gearbox, tooth root, load distribution, linear elastic fracture mechanics
Objavljeno: 01.06.2012; Ogledov: 875; Prenosov: 62
URL Povezava na celotno besedilo

5.
Evaluation of stress intensity factors using finite elements
Boštjan Zafošnik, Zoran Ren, Miran Ulbin, Jože Flašker, 2002, objavljeni znanstveni prispevek na konferenci

Opis: The paper describes a suitability of Virtual Crack Extension (VCE) method for numerical simulation of crack propagation under mixed mode loading. The suitability of VCE method was determined using The Compact-Tension-Shear (CTS), which is subjected to fracture Mode I, Mode II or mixed mode (Mode I + Mode II) loading. In mixed mode the crack kinks when fracture crack growth occurs. Kink angle is determined with VCE method, which is an energy method, maximum tangential stress (MTS) criterion, strain energy density (SED) criterion and experimental results. Determination of crack propagation angle using MTS and SED criterion is based in regard to the stress intensity factors KI and KII. Stress intensity factors are determined using the maximum energy release rate theory using complex J integral, crack opening displacement method and method of stresses extrapolation. Bigger is the rate between KII and KI, crack path, determined with VCE method, propagates more slowly to the kink angle, determined with experiment. The computational results show that the VCE method is suitable for crack propagation, when KI around the crack tip is dominant. In case where KII is dominant, crack does not kink immediately as in other two criteria. When KII dominates around a crack tip, MTS criterion is the most appropriate for determination of kink angle.
Ključne besede: fracture mechanics, stress intensity factors, CTS specimen, crack propagation, virtual crack extension method, strain energy density criterion, maximum tangential stress criterion
Objavljeno: 01.06.2012; Ogledov: 1510; Prenosov: 17
URL Povezava na celotno besedilo

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The influence of surface coatings on the tooth tip deflection of polymer gears
Boštjan Trobentar, Srečko Glodež, Jože Flašker, Boštjan Zafošnik, 2016, izvirni znanstveni članek

Opis: When designing gear drives made of polymer, the tooth tip deflection is a crucial parameter in respect to the proper gear drive operation. Excessive tooth tip deflection can lead to serious disturbances of gear meshing and consequently to increased noise and wear of the teeth flanks. In such cases the tooth tip deflection can be reduced through the use of stiff surface coatings on the tooth flanks. In this paper the influence of different coating materials and thicknesses on the tooth tip deflection of polymer gears is analysed using comprehensive finite element computational analysis. The numerical results obtained are then used to define an approximate equation for the calculation of gear tooth tip deflection for the coating material used and the thickness of the surface coating layer. The results show that the tooth tip deflection decreases with large values of the coating material Young’s modulus and with the coating layer thickness.
Ključne besede: polymer gears, surface coatings, tooth deflection, numerical analysis
Objavljeno: 27.03.2017; Ogledov: 366; Prenosov: 184
.pdf Celotno besedilo (578,86 KB)
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9.
Optimizacijski postopek v procesu zasnove zobnikov
Samo Ulaga, Jože Flašker, Boštjan Zafošnik, Iztok Ciglarič, 2001, izvirni znanstveni članek

Opis: V prispevku je opisano orodje za optimiranje geometrijske oblike zob kot dodatek k splošnim postopkom zasnove zobnikov. Algoritem omogoča zmanjšanje in enakomerno porazdelitev obrabe in jamičenja zob v ubiru. V postopku optimiranja upoštevamo dva glavna parametra, ki sta odvisna od geometrijske oblike zob: kontaktne napetosti in relativno drsenje. Oba sta odvisna od oblike kontaktne površine, ki pa je v veliki meri odvisna od koeficientov premikov profila. Če želimo doseči čim večjo življenjsko dobo zobnikov, moramo poiskati optimalne vrednosti koeficientov premikov profila, z upoštevanjem vseh preostalih robnih pogojev, ki so predpisani za zasnovo zobnikov. Uporabljen je algoritem adaptivnega izboljšanja mreže. V nadaljevanju prispevka je preverjena oblika zob, dobljena po predlaganem postopku. Prav tako so primerjane in ocenjene drsne razmere za obe obliki zob. Prikazana je možnost uporabe MKE v postopku snovanja zobnikov. Za izračun kontaktnih napetosti je uporabljen algoritem z metodo Lagrangeovih množiteljev po metodi končnih elementov, kontaktne površine pa so dodatno opisane s parametričnimi zlepki.
Objavljeno: 10.07.2015; Ogledov: 456; Prenosov: 29
URL Povezava na celotno besedilo

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