Causes of Variability in Gear Fatigue Testing

Fatigue testing of actual components can produce considerable variation in the data. This seems to be especially true for higher strength case hardened components such as gears. Long term fatigue data on gears has shown there may be up to a 9:1 difference between the high and low cycle samples tested under the same conditions. This paper presents a systematic approach to determining some of the causes of this variation. Hypoid gear sets were dynamometer tested at 6 month intervals to determine the contribution of each cause. This study shows that the dynamometer test set up, the heat treatment of the gears, the cutting of the gear teeth, and the heat of steel used all contribute to the variability. Several metallurgical factors were also examined for a correlation to fatigue life.