- Required information Bearing reactions R1 and R2 are exerted on the shaft shown in the figure, which rotates at 950 rev/min and supports an 10-kip bending force. Use a 1095 HR steel. Specify a diameter d using a design factor of nd= 1.6 for a life of 10 hr. The surfaces are machined. Assume kb = 0.85 and q = 0.85. -10 in- F 5 in -5 in d/5 R. R 1.4d- d/10 R. R 1 in- What is the fatigue strength at the design life for the shaft? The fatigue strength at the design life for the shaft is [ kpsi.