Evaluation of the service life of gear in regard to bending fatigue in a gear tooth root

A computational model for evaluation of service life of gears in regard to bending fatigue in a gear tooth root is presented. The fatigue process leading to tooth breakage is divided into crack initiation and crack propagation period. The Coffin-Manson relationship is used to determine the number of stress cycles N-i required for the fatigue crack initiation, where it is assumed that the initial crack is located at the point of the largest stresses in a gear tooth root. The simple Paris equation is then used for the further determination of the required number of loading cycles N-p for crack propagation from the initial to the critical length, where required material parameters have been determined previously with appropriate test specimens. The total number of stress cycles N for the final failure to occur is then a sum N = N-i + N-p.