In the process of gear transmission, the maximum shear stress caused by repeated rolling sliding contact leads to the plastic deformation of the tooth surface in the meshing area. Under the continuous accumulation of damage, the initial crack is formed on the tooth surface. Once the initial crack is formed on the tooth surface, the lubricating oil will enter into the crack under the action of contact pressure and form high pressure. The pressure acts on the inner wall of the crack and makes the stress concentration at the crack tip. The crack will turn to the tooth surface and expand until it expands to the edge of the tooth surface and forms spalling, leaving shallow pits on the tooth surface, namely micro pitting pits.
The location and length of the initial crack and the angle of relative movement direction are the key to simulate the micro pitting corrosion. Some scholars have found the law of initial crack germination through experimental research. In reference , through metallographic analysis of gears, it is found that the initial crack on the tooth surface is usually 20% to the direction of contact movement ° Angle. In reference , scanning electron microscope was used to observe the tooth surface with micro pitting. It was found that the depth of micro pitting was usually less than 10 μ m. The initial crack is 10% to the tooth surface °~ thirty ° Angle.