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Compression pre-stress of tubular torsion springs
Vinko Močilnik, Nenad Gubeljak, Jožef Predan, Jože Flašker, 2010, original scientific article

Abstract: This paper reports the results of a series of biaxial static compression and torsion experiments performed to evaluate the effects of static compression stress on the fatigue life of those smooth tubes made of high strength spring steel. The fatigue life of biaxial loaded springs depends, among others, on biaxial compression and torsion loading. A high shear loading ratio leads to low-cycle fatigue behaviour rather than high-cycle fatigue, because it was found that a crack was initiated at a local highly deformed area on surface of the specimen.The experimentally obtained results show a significant extension of fatigue strain life as a result of combining axial compression loading with torsion. Cracking behaviour was observed and it was noted that compression pre-stresses contribute to retardation of the fatigue crack initiation process and, consequently, contribute to the extension of fatigue life.
Keywords: fatigue, fatigue life, micro crack, multi axial stress state, pre-stressing, torsion, torsion bar springs, twist angle
Published: 11.07.2017; Views: 479; Downloads: 74
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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: 585; Downloads: 323
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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: 618; Downloads: 273
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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, original scientific article

Abstract: 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.
Keywords: polymer gears, surface coatings, tooth deflection, numerical analysis
Published: 27.03.2017; Views: 808; Downloads: 316
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Morphological and microstructural features of Al-based alloyed powders for powder-metallurgy applications
Borivoj Šuštaršič, Irena Paulin, Matjaž Godec, Srečko Glodež, Marko Šori, Jože Flašker, Albert Korošec, Stanislav Kores, Goran Abramović, 2014, professional article

Abstract: Besides advanced nano steels, polymers and ceramics, recently also light metals, i.e., Al, Mg and Ti based materials, have been recognized as future materials for different kinds of advanced applications. Al and its alloys have an acceptable price, excellent corrosive resistance, good mechanical and other physical properties. Therefore, they are also used in the powder-metallurgy (P/M) field. The P/M technology of Al materials is very demanding and has its own specifics compared to the sintering technology of iron and steel. A relatively large quantity of Al-based alloy powder is formed during the sand blasting of slugs and discs in the Talum Al factory, Kidričevo, Slovenia. Therefore, we analysed and investigated its practical usability for a production of advanced products using P/M technology. The formed Al-based powder was compared with the commercially available Al-based powders that are generally used for conventional sintering technology. In the first part of this paper we explain which types of Al-based powders are used for the production of sintered parts, what the required parameters are and why we considered them. Then, the results of theoretical thermodynamic analyses and investigations of the morphological and microstructural characteristics of the selected commercial Al-based powders are given, as well as their comparison with the Al powder formed during the sand blasting and its potential for P/M applications.
Keywords: Al-based alloy powders, morphology, microstructure, LM characterisation, SEM/EDS characterisation
Published: 17.03.2017; Views: 863; Downloads: 90
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Razvoj hibridnega stroja za delo na strmem terenu
Martin Kodrič, 2016, doctoral dissertation

Abstract: Obravnavamo problem vzdolžne obdelave nasadov na strmih kmetijskih površinah, ki se danes obdelujejo z vitelnimi obdelovalnimi stroji. Za ugotavljanje energijske učinkovitosti obdelave kmetijskih površin smo uvedli pojem izkoristek procesa obdelave kmetijskih površin, s katerim je opredeljeno razmerje med energijo delovnih priključkov in skupno vloženo energijo. Razvili smo koncept stroja, ki izkorišča razpoložljivo potencialno energijo in v času vožnje po strmi površini navzdol uporablja dva delovna priključka hkrati . Izdelali smo samovozni stroj z vitelnim in kolesnim pogonskim sklopom ter s hidrostatičnim prenosom moči. Prednosti novega stroja smo dokazali z metodo nevronskih mrež. Napisali smo algoritem za ugotavljanje in napovedovanje izkoristka procesa obdelave strme kmetijske površine. Rezultati izboljšav so manjša poraba goriva, manjša količina proizvedenega CO2 in manjši stroški obdelave.
Keywords: strma kmetijska površina, potencialna energija, izkoristek procesa obdelave, vitelni stroj, hibridni pogon, nevronske mreže, metoda matrik
Published: 25.08.2016; Views: 1240; Downloads: 117
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A theoretical and numerical study of an additional viscosity term in a modified elasto-plastic friction model for wet friction clutch simulations
Tomaž Petrun, Jože Flašker, Marko Kegl, 2013, original scientific article

Abstract: This paper deals with a theoretical and numerical study of various viscosity terms in the modified elasto-plastic friction model and its influence on the resulting friction force-torque, transmitted through the contact of the friction clutch. Various simple viscous definitions for fluids considering shear rate dependent viscosity were investigated. As a basis for the research the Carreau fluid model was chosen, since it can describe Newtonian, dilatant and pseudo plastic fluids. Besides of theoretical investigations, numerical simulations at realistic friction clutch operation conditions were carried out. The results were compared to the results of a validation case for a dry friction clutch simulation with the modified elasto-plastic friction model. This research showed significant differences between various viscosity definitions and revealed the drawbacks of such a simplified approach. In addition to viscosity, a possibility to calculate the generated heat due to friction and its influence on the contact temperatures is discussed briefly. The basic theory and equations are given along with the directions for future work. The requirements for an accurate temperature calculation in the friction contact are outlined.
Keywords: friction model, friction clutch simulation, simple viscosity models, Carreau fluid
Published: 21.12.2015; Views: 758; Downloads: 59
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Numerično simuliranje površinske utrujenostne razpoke na zobeh zobnikov
Gorazd Fajdiga, Jože Flašker, Srečko Glodež, Zoran Ren, 2000, original scientific article

Abstract: V tem prispevku je predstavljen dvodimenzijski računski model za simuliranje širjenja površinsko začetne utrujenostne razpoke v stičnem področju dveh zobnih bokov zobnikov. Diskretiziran model zoba zobnika je obremenjen s pravokotno obremenitvijo (Hertzov stični tlak), strižno obremenitvijo (trenje med zobnimi boki zobnikov) in dodatno stično silo, ki je posledica elastohidrodinamičnih (EHD) pogojev mazanja. Za določitev širjenja utrujenostne razpoke od začetne do kritične dolžine, ko se delček materiala odlomi od površine in povzroči nastanek jamice, je uporabljen postopek J-integrala v okviru metode končnih elementov. Primerjava računskih in eksperimentalnih rezultatov kaže, daje predstavljeni model primeren za spremljanje širjenja površinske utrujenostne razpoke pri stični obremenitvi in ga kot takega lahko uporabimo pri napovedovanju pojava jamičenja na stično obremenjenih elementih, kakor so zobniki, ležaji, kolesa itn.
Keywords: strojni elementi, zobniška gonila, lomna mehanika, utrujanje, jamičenje, mazanje, kontaktni problemi, dotikalne površine
Published: 10.07.2015; Views: 844; Downloads: 52
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Optimizacijski postopek v procesu zasnove zobnikov
Samo Ulaga, Jože Flašker, Boštjan Zafošnik, Iztok Ciglarič, 2001, original scientific article

Abstract: 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.
Published: 10.07.2015; Views: 669; Downloads: 39
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Računski model za preračun upogibne trdnosti zobnikov
Srečko Glodež, Jože Flašker, Damir Jelaska, Janez Kramberger, 2002, original scientific article

Abstract: V prispevku je predstavljen računski model za določitev dobe trajanja zobnikov glede na trdnost v zobnem korenu. Potek utrujanja, ki vodi do zloma zoba v korenu, sestoji iz nastanka in širjenja utrujenostne razpoke. Za določitev potrebnega števila obremenitvenih ponovitev Ni za nastanek utrujenostne razpoke je uporabljen Coffin-Mansonov zakon, pri katerem je predpostavljeno, da je začetna razpoka locirana na mestu največjih napetosti v zobnem korenu. Za nadaljnje širjenje razpoke je uporabljen znani Parisov zakon, pri katerem so potrebne materialne veličine določene poprej na podlagi ustreznih testnih preskušancev. Funkcijska odvisnost med faktorjem intenzivnosti napetosti in dolžino razpoke K=f(a), ki je potrebna za določitev potrebnega števila obremenitvenih ciklov Np za razširitev razpoke od začetne do kritične dolžine, je izračunana numerično z metodo končnih elementov. Skupno število obremenitvenih ponovitev N za pojav končne poškodbe je vsota N=Ni+Np. Čeprav nekateri vplivi (nehomogeni material, gibanje dislokacij) pri preračunih niso upoštevani, je predstavljen računski model zelo primeren za določitev dobe trajanja zobnikov, saj so tukaj predstavljeni numerični postopki hitrjši in cenejši v primerjavi z eksperimentalnim delom.
Published: 10.07.2015; Views: 996; Downloads: 38
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