A 1050 HR steel has a mean ultimate tensile strength of S=725 MPa and a mean yield strength of 415 MPa.The endurance limit is 362 MPa.This material is used to manufacture the shaft,which is shown in the figure.The shaft has a fatigue stress-concentration factors k=1.66 and k=1.63.The rotating shaft is subjected to bending moment of 145kNmm and the steady torsion moment is125kNmm.