Suppose that the fatigue data for the steel alloy in Problem 8.24 were taken for bending-rotating tests and that a rod of this alloy is to be used for an automobile axle that rotates at an average rotational velocity of 600 revolutions per minute. Give the maximum lifetimes of continuous driving that are allowable for the following stress levels:

(a) 450 MPa (65,000 psi),

(b) 380 MPa (55,000 psi),

(c) 310 MPa (45,000 psi), and

(d) 275 MPa (40,000 psi)?