Different failure forms of gear transmission are unlikely to occur simultaneously on a pair of gears, but they affect each other. For example, the pitting corrosion of the tooth surface will aggravate the wear of the tooth surface, and the serious wear will lead to the fracture of the tooth. Under certain conditions, the failure of tooth surface is mainly due to pitting corrosion. Therefore, when designing gear transmission, the possible main failure forms should be analyzed according to the actual working conditions to determine the corresponding design criteria.
For the gear transmission with closed soft tooth surface (hardness ≤ 350hbw), the lubrication condition is good, and the tooth surface pitting corrosion will be the main failure form. In the design, it is usually designed according to the contact fatigue strength of the tooth surface, and then checked according to the bending fatigue strength of the tooth root.
For gear transmission with closed hard tooth surface (hardness > 350hbw), it has strong pitting corrosion resistance and high possibility of tooth fracture. In design and calculation, it is usually designed according to the bending fatigue strength of tooth root and checked according to the contact fatigue strength of tooth surface.
The main failure form of open gear transmission is tooth surface wear. However, due to the complex wear mechanism and no mature design and calculation method, it can only be calculated according to the bending fatigue strength of the tooth root, and the tooth thickness can be increased by increasing the modulus by 10% ~ 20%, so that it has a long service life, so as to consider the influence of wear.