고체역학 (Beer) — Torsion: Problem 3.101

3.101 A 3-ft-long solid shaft has a diameter of 2.5 in. and is made of a mild steel that is assumed to be elastoplastic with \(\tau_Y = 21 \text{ ksi}\) and \(G = 11.2 \times 10^6 \text{ psi}\). Determine the torque required to twist the shaft through an angle of (a) \(2.5^\circ\), (b) \(5^\circ\).