STRESS ANALYSIS OF GEARS

BENDING STRESS

In AGMA terminology, bending and pitting resistance (contact stress) are called stress numbers

The fundamental equation for bending stress in SI units is :

Where

is the tangential transmitted load

 is the overload factor                             (Table 1-3, page 29)

 is the dynamic factor                            (Eqn. 14-27 through Eqn. 14-29, page 920)

 is the size factor                                    (Eqn. (d), page 923)

 is the net face width of the narrower member    

 is the transverse metric module

 is the load distribution factor                  (Eqn. 14-30 through Eqn. 14-35, page 923-24)

 is the geometry factor for bending strength       (Fig. 14-6, page 917)

CONTACT STRESS

The fundamental equation for pitting resistance (contact stress) is

 is an elastic coefficient,          (Table 14-8, page 921)

 is the surface condition factor for pitting resistance    (equals 1)

 is the pitch diameter of the pinion

 is the geometry factor for pitting resistance       (Eqn. 14-23, page 919)

Calculate bending and contact stresses for both pinion and gear

Assume a suitable factor of safety for the gears’ material

Calculate allowable bending stress number and allowable contact stress number for the pinion

Use Fig. 14-2 and Fig. 14-5 to read hardness in both the cases

Take larger of the two values as hardness of the pinion

Repeat the same procedure to find out hardness of the gear