Effect of Shot Peening on Surface Fatigue Life of Carburized and Hardened AISI 9310 Spur Gears

Gear surface fatigue endurance tests were conducted on two groups of 10 gears each of carburized and hardened AISI 9310 spur gears manufactured from the same heat of material. Both groups were manufactured with standard ground tooth surfaces. The second group was subjected to an additional shot-peening process on the gear tooth surfaces and root radius to produce a residual surface compressive stress. The gear pitch diameter was B.89 em (3.S in.). Test conditions were a gear temperature of 350 K (170 °F). a maximum Hertz stress of 1.71×l0⁹ N/m² (248000 psi). and a speed of 10 000 rpm.

The shot-peened gears exhibited pitting fatigue lives 1.6 times the life of the standard gears without shot peening. Residual stress measurements and analysis indicate that the longer fatigue life is the result of the higher compressive stress produced by the shot peening. The life for the shot-peened gear was calculated to be 1.5 times that for the plain gear by using the measured residual stress difference for the standard and shot-peened gears. The measured residual stress for the shot-peened gears was much higher than that for the standard gears.