Evaluation of the Strength of Carburized Spur Gear Teeth Based on Fracture Mechanics

Abstract

A method is developed to simulate fatigue crack growth in a carburized gear tooth based on two-dimensional linear fracture mechanics. In the simulation, the stress intensity factor is calculated by means of a finite-element method (FEM) which takes into account the effect of residual stress. The fatigue crack growth rates in the case layer are estimated experimentally, and they are expressed by an experimental formula. A strength evaluation procedure for carburized gears is then proposed on the basis of the developed method of simulation. In the procedure, the critical length of the initial crack which is obtained from the fatigue strength is assumed to be equal to the crack length evaluated from the threshold stress intensity factor, and the basic load capacity is estimated. The critical lengths are evaluated for variously treated gears and illustrated as a function of surface condition.