Review of mathematical and experimental models for determination of service life of gears

For designing machines and devices the dimensioning with respect to service life is increasingly taken into account. This applies also for gearing which are still today one of very important components of almost all machines. We have developed a stochastic model for determination of service life of gears. In our model we propose a new parameter by which we describe the fracture mechanics conditions in the tooth root where the defects, causing destruction, occur statistically most frequently as shown. We named that factor the tooth stress intensity factor Z. The value of the factor Z is related to dislocation, propagation of the plastic zone, deformation and orientation of grain in case of short cracks and stress intensity factor K in case of long cracks. For determination of the service life for the area of short cracks we used Bilby, Cottrell and Swinden model which is based on the theory of continuously distributed dislocations and we complemented it with random generation of structure of material before cracks. For the long crack we have developed a stochastic model for determination of service life of gears. For confirm mathematical models we developed different non-standard test pieces and on this pieces we used combination of mixed experimental methods. The aim of these combinations was to obtain as complete information about the individual influences as possible and to determine the interaction between different fracture mechanic magnitudes. In this way we confirmed the mathematical models as a whole and also determined some physical interpretations in models. With this we were able to ensure that the presented model is not purely a mathematical model. (C) 2003 Elsevier Ltd. All rights reserved.