The solid shaft is made of an elastic-perfectly plaslic material as shown. Determine the t...

The solid shaft is made of an elastic-perfectly plaslic material as shown. Determine the torque T needed to form an elastic core in the shaft having a radius of py = 20 mm.  If the shaft is 3 m long, through what angle does one end of the shaft twist with respect to the other end? When the 3 torque is removed, determine the residual stress distribution in the shaft and the permanent angle of twist.