고체역학 (Gere) — Torsion: Problem R-3.1

R-3.1 A brass rod of length \( L = 0.75 \text{ m} \) is twisted by torques \( T \) until the angle of rotation between the ends of the rod is \( 3.5^\circ \). The allowable shear strain in the copper is \( 0.0005 \text{ rad} \). The maximum permissible diameter of the rod is approximately: (A) \( 6.5 \text{ mm} \) (B) \( 8.6 \text{ mm} \) (C) \( 9.7 \text{ mm} \) (D) \( 12.3 \text{ mm} \)