Prediction of residual surface fatigue life of power transmission gears using X-ray diffraction method

Abstract

A new technique using a non-destructive inspection to predict the residual surface fatigue life of power transmission gears has recently attracted interest. This technique is advantageously applied to the preventive maintenance of a vehicle transmission, and also useful for developing power transmission gears with high reliability. However, the study of such a prediction has not yet been reported. The authors have carried out an experimental research concerning the subject using the X-ray diffraction method. The full-width at half-maximum (FWHM) was measured on the tooth surfaces of a pair of carburized gears by an X-ray diffractometer during a gear surface fatigue endurance test to investigate the progress of the surface fatigue. The results showed that the FWHM on the tooth surface fell rapidly at the beginning of the running. After that, under the condition of constant driving torque, the FWHM fell gradually in a higher Hertzian pressure area during the endurance running. On the other hand, the FWHM in a lower Hertzian pressure area was approximately stable. When the driving torque was changed during endurance running, the distinctive behavior of the FWHM was observed. Tooth surface damage occurred in a higher Hertzian pressure area when the normalized FWHM, newly developed by the authors, on the tooth surface decreased to a certain value. The authors propose a prediction method of the residual surface fatigue life of power transmission gears using the characteristic curve that expresses the relation between the normalized FWHM and the gear surface fatigue life.