The main shaft of a particular machine is to continuously transmit 25.0 ft-lbs of torque (say, along the z-axis). It is also subjected to a bending moment of magnitude 3.0 ft-lbs, which is fixed in space, such that the bending stress each point of the cross section is a sinusoidal function of time.
The following data apply:
material = UNS G41300 Steel
rotation frequency = 10.0 Hz
d = 0.40 in
ground surface finish
operating temperature = 425oC
all fatigue stress concentration factors = 1
It is desired that the specimen last 1 full year under continuous operation. It is also desired to introduce a 95% reliability associated with the endurance limit (i.e, we want to be 95% sure that the part in use has an endurance limit equal or greater than the assumed value).
Determine the safety factor against fatigue failure for the specified life.