An aluminum tube of 250 mm long (E = 70 GPa) of 36 mm outer diameter and 28 mm inner diameter might be closed at both ends by means of single-threaded screw-on covers of 1.5 mm pitch. With one cover screwed on tight, a solid brass rod (E = 105 GPa) having 25-mm diameter is placed within the tube and the second cover is screwed on. As the rod is slightly longer than the tube, it is viewed that the cover should be forced against the rod by rotating it one-quarter of a turn before it can be tightly closed. Find (i) the average normal stress in the tube and in rod, (ii) deformations of the tube and of rod.