Problem 4. [10 Marks] (a) A solid shaft of diameter D=50 mm rotates and carries the minor shock loading as shown in figure. Calculate the fatigue safety factor n and yielding factor of safety ny for the shaft. Given: D=75 mm, Sy=550 MPa, Su=660 MPa. The torque fluctuates 5% each way from the mean value, and the shaft is to be machined from unnotched steel. [5 Marks] (b) Determine the value of the critical speed of rotation for the simply supported shaft carrying two loads at C and D as illustrated in figure. D=50mm, E=210GPa and density p = 7800 kg/m³. [5 Marks] -0.3 m 1 kN 0.5 m 5 kN 0.5 m 0.15 m 1 m 120 mm 0.5 m 120 mm 2 kN 6kN 2 kN 6 KN