Crack Propagation in Tooth Root: A Comparison Between Pulsator Test and Running Gears

Tooth root fatigue fracture is a critical gear failure mode in which the tooth root breaks because of the repetition of bending load. The most widely adopted procedure for evaluating root strength is through pulsator testing. However, this test method does not present gears in meshing conditions. When focusing on the limited-life region of the SN curve, certain differences are observed between pulsator and running gear tests: A gear under meshing conditions presents a lifetime comparable, if not even higher, than that within pulsator testing. This study investigates the role of crack propagation in the tooth root and how it could explain this difference.