고체역학 (Beer) — Torsion: Problem 3.104

3.104 The shaft AB is made of a material that is elastoplastic with \(\tau_Y = 90 \text{ MPa}\) and \(G = 30 \text{ GPa}\). For the loading shown, determine (a) the radius of the elastic core of the shaft, (b) the angle of twist at end B. Given from Fig. P3.104: Applied torque \(T = 300 \text{ N}\cdot\text{m}\) Shaft length \(L = 2 \text{ m}\) Shaft radius \(c = 12 \text{ mm} = 0.012 \text{ m}\)