Conception and development of improved analytical prediction models for fatigue induced tooth breakage due to cyclic bending in spur gear teeth

An analytical prediction model for bending fatigue of spur gear teeth which characterizes bending fatigue as a two stage process is considered. The modelling of fatigue crack initiation, the first stage of bending fatigue, is discussed. Modelling of fatigue crack propagation, the second stage of bending fatigue, is performed employing an elastic-plastic description of a growing fatigue crack. The model considers plasticity induced fatigue crack closure in the presence of residual stress fields, and is based on the Dugdale model, modified to leave plastically deformed material along the crack surfaces as the crack advances.; To allow implementation of the model to cracked spur gear teeth under static mesh loading, the effect of a pinion crack on pinion tooth loading is investigated analytically in a static spur gear mesh model which considers contact off the line of action. The stiffness of a cracked spur gear tooth is predicted, and is a function of the mode I and mode II stress intensity factors for the cracked tooth. Stress intensity factors for cracked spur gear teeth are obtained through application of the Bueckner weight function, in conjunction with spur gear tooth stress fields computed through a conformal mapping of the tooth onto an elastic half-plane.; Stress intensity factors for cracked spur gear teeth computed using the conformal mapping and weight function compare well with finite element predictions when cracks are small. The elastic-plastic fatigue crack propagation model is used to predict fatigue crack propagation in a carburized and shot peened steel spur gear during a single tooth fatigue test, and comparisons are made with existing experimental data.