고체역학 (Gere) — Torsion: Problem 3.11-11

3.11-11 A tubular aluminum bar (\(G = 28\text{ GPa}\)) of square cross section (see figure) with outer dimensions \(50\text{ mm} \times 50\text{ mm}\) must resist a torque \(T = 300\text{ N}\cdot\text{m}\). Calculate the minimum required wall thickness \(t_{\min}\) if the allowable shear stress is \(20\text{ MPa}\) and the allowable rate of twist is \(0.025\text{ rad/m}\).