THE 'TRUE' BENDING STRESS in SPUR GEARS

It is well known from the literature that the true bending stresses at the tooth root of spur gears are quite different from the nominal values that are utilized for the calculation of load capacity, either by standards or usual design rules. No problems arise in using a load capacity rating when the simplified values are compared with the results of bending fatigue tests whose limits are calculated with the same schematic method. But the 'true'stress at the tooth root has different trends and values, and the designer must be aware of this difference, especially for light gears with narrow ribs and rims. In this paper, an accurate FEM analysis has been done of the 'true'stress at tooth root of spur gears in the function of the gear geometry. The obtained results confirm the importance of these differences.