The drilled shaft was permanently fixed at the left end and loaded with a moment of 30 kNm as shown in the drawing. Assume G=80 GPa. Calculate and draw the graphs of torsional moments, shear stresses, and the angle of twist: \(M(x), \tau(x), \varphi(x)\). The permissible angle of twist \(\varphi_{dop}=0,4^o\), torsional strength \(\tau_{dop}=60\ MPa\). Dimension the diameter of the rod D.