Pitting failure of gears.
thesisposted on 19.11.2015, 08:59 by R. A. Onions
Failure due to pitting fatigue has been investigated under controlled laboratory conditions. The investigations used both a realistic laboratory test rig using 1/2" face width gears and the geometrically simpler simulation of gears using a disc machine. The results obtained substantiated earlier work of Way and Dawson. The initiation and propagation mechanisms are generally considered to hold true. However, the gear tests showed that failure could occur much more readily than with discs and therefore the application of disc tests to gears must be viewed with caution. The results suggest a fundamental difference between the pitting behaviour of gears and discs. The second part of the thesis is of a more theoretical nature. A theory of surface contact was developed along the lines of that by Greenwood and Williamson using a surface model developed by Whitehouse and Archard. These results show that a distribution of asperity curvatures increases the probability of plastic deformation. The plasticity index has been redefined in terms of a convenient two parameter defirition of surface topography. The theory has been applied to results obtained from a typical ground surface of hardened steel; when the anisotropy, which is part of such surfaces, is taken into account it is shown that only a small proportion of the contacting asperities are plastically deformed. The limitation of this form of model is discussed and a second approach is put forward using digital techniques. Theory has been developed to enable the contact of surface profiles to be simulated in a computer and the interference areas so formed have been related to the real Hertzian deformed areas of two rough surfaces. The approach is equally applicable to run- in surfaces which are not represented by existing models. The implications of this work for future research are discussed; the need for a fuller understanding of partial and micro elastohydrodynamic lubrication by theory and experiment is stressed.