Dragan Žeželj

Utjecaj kontaktnog pritiska i brzine klizanja na temperaturu i faktor trenje u kontaktu s uzrocima od PET-a

Original scientific paper The use of polymeric materials has been growing steadily. A more extensive use of polymers as bearing materials will be made possible by a better knowledge of the properties of particular materials and their compatibility in a particular application. Poly(ethylene terephthalate) (PET) with the addition of Polytetrafluorethylene (PTFE) shows potential for being used as a material for machine parts rotating at lower loads due to its good ratio between manufacturing costs and mechanical properties. The use of PET in a PET/PET combination has been tested in three working points, with a lubricant applied once in each run and with three different values of sliding speed and of load. The change in temperature which occurs in the vicinity of the outlet zone of the contact at the end of the sliding path after 9 hour operation is presented. The applied method and temperature measurement are explained. The distribution of obtained maximum and average temperatures in the load range 9 ÷ 18 MPa and the sliding speed range 0,8 ÷ 2 m/s is shown for single working points. In addition, the effects of lubricant application on the increase in the magnitude of the load carrying capacity and on the decrease in the value of friction coefficient are shown in comparison with the reference values of temperature and friction coefficient in the dry contact operation.

Effect of rotational speed on thin-rim gear bending fatigue crack initiation life

Thin-rim gears are often used in aircraft applications in order to reduce weight. The objective of this study is to investigate the effect of rotational speed (centrifugal force) on bending fatigue crack initiation life of thin-rim gear manufactured from case carburized 14NiCrMo13-4 steel. Stresses in gear are determined from two-dimensional finite element model, assuming plane stress conditions. The fact that, in actual thin-rim gear operation, a significant reversed stress occurs at the root of the tooth adjacent to the loaded tooth is considered. Material is assumed to be homogenous, isotropic and linear elastic. Elastic strains are calculated from obtained stresses and corrected using Neuber’s rule to account plasticity effects. The number of load cycles required to initiate bending fatigue crack is predicted using strain-life approach for variety of gear rotational speeds and rim thicknesses. Strain-controlled fatigue properties were approximated from material hardness, while the mean stress as well as residual stress effects are included through Morrow’s mean stress correction. The proposed approach is validated by comparison with available experimental data from literature and used for parametric studies. Predicted numbers of load cycles required to initiate potential bending fatigue crack are presented for the variety of cases studied.

Integracija privatnih društvenih mreža u PLM sustave

Danasnji PLM sustavi pružaju ogranicenu podrsku komunikaciji između konstruktora i drugih srodnih ljudskih subjekata u razvoju proizvoda. Sociotehnicki model sugerira da je komunikacija bitan cimbenik pri uspostavljanju sustava sljedivosti te u slucajevima kada postoji potreba za boljim razumijevanjem procesa razvoja proizvoda. U radu se predlaže ukljucivanje privatne drustvene mreže u PLM sustav u cilju poboljsanja upravljanja komunikacijom tijekom procesa razvoja proizvoda u cilju dohvacanja konstrukcijskog znanja.