1. Računski model za preračun upogibne trdnosti zobnikovSrečko 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 in DKUM: 10.07.2015; Views: 1594; Downloads: 52
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2. Numerical modelling of crack growth in a gear tooth rootSrđan Podrug, Srečko Glodež, Damir Jelaska, 2011, original scientific article Abstract: A computational model for determination of crack growth in a gear tooth root is presented. Two loading conditions are taken into account: (i) normal pulsating force acting at the highest point of the single tooth contact and (ii) the moving load along the tooth flank. In numerical analysis it is assumed that the crack is initiated at the point of the largest stresses in a gear tooth root. The simple Paris equation is then used for a further simulation of the fatigue crack growth. The functional relationship between the stress intensity factor and crack length K=f(a), which is needed for determining the required number of loading cycles N for a crack propagation from the initial to the critical length, is obtained using a displacement correlation method in the framework of the FEM-method considering the effect of crack closure. The model is used for determining fatigue crack growth in a real gear made from case carburised and ground steel 14CiNiMo13-4, where the required material parameters were determined previously by appropriate test specimens. The results of the numerical analysis show that the prediction of crack propagation live and crack path in a gear tooth root are significantly different for both loading conditions considered.
Keywords: zobniki, utrujanje, širjenje razpoke, numerično modeliranje, gears, fatigue, crack growth, numerical modelling
Published in DKUM: 10.07.2015; Views: 1347; Downloads: 85
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3. Closed form expression for fatigue life prediction at combined HCF/LCF loadingDamir Jelaska, Srečko Glodež, Srđan Podrug, 2003, original scientific article Abstract: For combined HCF/LCF loading, whose stress history is simplified so that it consists of one LCF stress block with a number of cycles equal to the number of start-up in-service operations and one HCF stress block with all HCF cycles summed-up, we derived the closed form expression for estimating both the crack initiation life and the crack propagation life at combined HCF/LCF loading. As an example of use, Smith and Haigh diagrams were obtained for titanium alloy (Ti-6Al-4V) components, which enable to estimate the fatigue strength for the designed fatigue life, known load ratio and certain number of HCF cycles per one combined stress block.
Keywords: machine elements, fatigue, service life prediction, crack initiation, crack growth, stress history
Published in DKUM: 01.06.2012; Views: 2594; Downloads: 53
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4. Influence of different load models on gear crack path shapes and fatigue livesSrđan 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 in DKUM: 31.05.2012; Views: 1708; Downloads: 95
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