Development of bending fatigue design of gears based on test specimens

Different design methods against bending fatigue are reported in ISO 6336 Standard. The Standard suggests primarily the method based on reference test gears and provides the relevant fatigue curves. Additionally, the Standard suggests to use specimens (and not gears) to generate the reference fatigue curves to design gears, but it also advices that specimens-based methods can be used when gears are not available and are particularly useful for comparing fatigue performances of gear materials relative to one another. The purpose of the present paper is to evaluate the accuracy and to propose an improvement of the specimens-based methods mentioned in ISO Standard when applied to design gears against bending fatigue. It was found that the specimens-based methods are as accurate as the reference gears-based method, provided that the material notch sensitivity factor is properly calibrated on the experimental results obtained from specimens.