*5-88. A rod is made from two segments: AB is steel and BC is brass. It is fixed at its ends and subjected to a torque of T = 680 N. m. If the steel portion has a diameter of 30 mm, determine the required diameter of the brass portion so the reactions at the walls will be the same. Gst = 75 GPa, Gbr = 39 GPa. 5-89. Determine the absolute maximum shear stress in the shaft of Prob. 5-88. с B 1.60 m 680 N·m E A 0.75 m Probs. 5-88/89