Effect of friction in a single-tooth fatigue test

The primary objective of the single tooth fatigue test is to generate gear-tooth bending fatigue data at a comparatively low price. Assuming a negligible influence on fatigue data, the effect of friction is not evaluated. The aim of this study is to evaluate the effect of tooth friction on tooth bending fatigue life and on the location of the crack initiation site in a single-tooth fatigue test of case carburized steel spur gear. By using Neuber’s rule, tooth root stresses predicted by means of two-dimensional elastic finite element analysis are translated into estimates of elastic-plastic stress and strain behaviour. The fatigue life and location of crack initiation site are predicted on the basis of the strain-life approach with consideration of mean stress, surface finish and residual stress effects. Two load models are considered. In the first load model, which represents the operating principle commonly used in practice, the test tooth is loaded through the actuating arm. In the second one, which is proposed in this study, the test tooth supports the reaction through the fixed anvil. In both load models, the test tooth is contacted at the highest point of single tooth contact, while the other one is contacted at a lower position along the tooth profile. The computational model is validated against experimental crack initiation lives from literature. The study revealed that friction has a more significant impact on tooth bending fatigue life and location of the crack initiation for the first load model as opposed to the second one.