1) A stepped steel shaft, shown below, is used in a spur gear reducer. The shaft is subjected to a constant axial stress (A=40 MPa), a constant bending moment that results in a variable stress (M=60 MPa) due to loads by bearings and gears, and a steady torque (T=80 MPa). However, these stress values do not take into account stress concentration factors. The shaft has a D=45 mm, d=30 mm, and r=6 mm, resulting in $k_{f,bend}$=1.34, $k_{f,axial}$=1.48, and $k_{f,tor}$=1.2. The shaft is made of steel with $S_u$=1006 MPa, $S_y$=648 MPa, and $H_B$=229. The size of the shaft results in a gradient factor of $C_G$=0.9. The shaft has a fine-ground finish. A 90% reliability is required. Verify the stress concentration factors are correct for this shaft geometry. Calculate the safety factor relative to infinite life ($10^6$ cycles). If the safety factor is less than one (i.e., shaft fails), find the number of cycles to failure.