1) The section of shaft shown in the figure is to be designed to approximate relative sizes of d = 0.75D and r = D/20 with diameter d conforming to

that of standard metric rolling-bearing bore sizes. The shaft is to be made of AISI 4140 steel, heat-treated to obtain minimum strengths in the shoulder area of 951 MPa ultimate tensile strength and 834 MPa yield strength with a Brinell hardness not less than 285. At the shoulder the shaft is subjected to a completely reversed bending moment of 35 x 10° N.mm, accompanied by steady torsion of 22.5 x 10' N.mm.Surfaces are machined.