Calculate the tooth bending fatigue stress for the more critical of the pinion or the gear.

1.For the Coniflex® bevel gearset described in problem 15-53, the following information has been tabulated or calculated: 630 in-lb 6 2.50 inches 1.15 inches 15 teeth 45 teeth Further, it is proposed to use Grade 2 AISI 4140 steel nitrided and through-hardened to BHN 305 for both the pinion and the gear. Other known design information includes the following items:

1. Input power is supplied by an electric motor.

2. AGMA quality is desired.

3. The gear is straddle mounted with a closely positioned bearing on each side, but the pinion overhangs its support bearing.

4. A design life of 109 cycles has been specified. A reliability of 99 percent is required, and a design safety factor of at least 1.3 is desired. Do the following:

a. Calculate the tooth bending fatigue stress for the more critical of the pinion or the gear.

b. Determine the tooth bending fatigue strength for the proposed AISI 4140 steel material corresponding to a life of 109 cycles. Qv = 8 Ng = Np = b = dp = Pd = T.

c. Calculate the existing safety factor for the proposed design configuration, based on tooth bending fatigue as the governing failure mode. Compare this with the desired design safety factor, and make any comments you think appropriate.