Abstract: Application of statistical fracture and experimental approval of two-slope hypothesis indicted research development on life prediction of gears. According to experimental results of fracture for carburized steel 20Cr2Ni4 comparing with new standards of AGMA2001---B88 and ISO6336—93, it is clear that the propagation slope m1 of small crack at first stage is the same as the S-N curve slope of material in large stress cycle number regime.

Key words: Fatigue, Fracture mechanics, Gear