Exploring Mechanisms of Residual Stress Instability along a Gear Contact Fatigue Test

The induced residual stresses along the gear manufacturing chain became a promising solution to increase the fatigue lifetime in face of the demands for high load carrying capacities. The non-static nature of the residual stress state during operation represents a challenge in determining its impact in the fatigue lifetime, as competing mechanisms of relaxation and martensitic transformation are present. This investigation’s objective is the characterization of the residual stress in-depth profile evolution of ground and shaved gears during the contact fatigue operation. Samples of both finishing routes were tested in a power circulating test rig. Residual stress measurements in the gear’s teeth were taken at the as manufactured condition, after 1000 cycles and at the test’s end. Ground gears, as manufactured, presented a steep residual stress gradient along the depth, in contrast with the shaved ones, contributing to the relaxation during operation of the formers. In shaved gears, retained austenite transformation increased the compressibility during the tests. The results indicate that the finishing route has a decisive impact on the residual stresses time-stability, since the plasticizing mechanisms define the in-depth residual stress gradients. Along the fatigue tests, the distinct profiles led to distinct relaxation tendencies between the assessed finishing routes.