Research of Force-Fitted Gear : 3rd Report, On the Bending Fatigue Strength of Shrinkage-Fitted Gears

Theoretical analysis of stress at the root fillet of the shrinkage-fitted gears correspond with that of the force-fitted gears in the two-dimensional theory of elasticity. But practical stresses induced at the root fillet of gear tooth are not equal in both cases. To explain the reason for this, the residual stresses induced and their change at the loaded side and the opposite side of the root fillet, roughness and hardness at the root fillet of tooth, and bending fatigue strength of the shrinkage-fitted gears were investigated. Results obtained are as follows. (1) Bending fatigue strength of the shrinkage-fitted gears show lower values in comparison with that of the force-fitted gears. (2) This decrease of bending fatigue strength is caused by the stress at the root fillet of tooth induced by air-cooling, which occurs in taking out the gear rim from electric furnace to shrinkage-fit. (3) Practical formulas for the residual stress along the fillet curve of the shrinkage-fitted gears are introduced by modifying formulas for the force-fitted gears.