Before calculating the tooth root stress of the gear, it is necessary to find the exact position of the load point E on the tooth top surface of the gear, as shown in the figure.
According to the national standard GB / T 3480-1997, the calculation formula of tooth root stress of test gear can be obtained
It is the tooth profile coefficient when the load acts on point E. according to the tooth profile coefficient calculation formula given in gb3480-184.108.40.206:
Mn normal modulus of gear, mm;
An – pressure angle of normal dividing circle, degrees;
SFN – tooth thickness of dangerous section, mm, calculation formula:
According to the calculation in Figure, it can be concluded that:
a FEn=28.7 °； hFE=18.87 mm； SFn=24.21 mm。
YS – stress correction factor, which can only be used in combination with tooth profile factor YF. For the tooth profile angle an is 20 ° According to gb3480-220.127.116.11, the tooth profile coefficient formula is as follows:
L-ratio of tooth thickness and bending arm at dangerous section of tooth root.
According to the relationship between the data in Figure 18, we can get the following results ρ F=8.32 。