Mechanical Engineering Design 7-3 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 rolling- bearing bore sizes. The shaft is to be made of SAE 2340 steel, heat-treated to obtain minimum strengths in the shoulder area of 1206.625 MPa ultimate tensile strength and 1103.200 MPa yield strength with a Brinell hardness not less than 370. At the shoulder the shaft is subjected to a completely reversed bending moment of 67.800 N-mm hoquo accompanied by a steady torsion of 45.200 N mm. Use a design factor of 2.5 and size the shaft for an infinite life using the DE-Goodman criterion. Problem 7-3 Section of a shaft containing a grinding-relief groove. Unless bre otherwise specified, the diameter at. the root of the groove d, = d - 2r, and though the section of diameter d is ground, the root of the groove is still a machined surface. 71 STU noit The rotating solid steel shaft is simply supported by bearings at points B and C and