H T A stepped shaft as shown in the figure above is to be constructed by welding two shafts, with diameters H=100 mm and h=80 mm, together. The stepped shaft will be used to transmit a torque of 7=3500 Nm. The shafts are made of the same grade of steel with the shear modulus G of 76 GPa. What minimum shoulder fillet radius, r, should be chosen in the construction so that the maximum shear stress in the shaft would not exceed 45 MPa? Choose the one option that is closest to the correct answer. 4.8 mm 6.6 mm 9.8 mm 12.3 mm 14.9 mm O 17.4 mm