고체역학 (Gere) — Torsion: Problem 3.2-2

3.2-2 A plastic bar of diameter \( d = 56 \text{ mm} \) is to be twisted by torques \( T \) (see figure) until the angle of rotation between the ends of the bar is \( 4.0^\circ \). (a) If the allowable shear strain in the plastic is \( 0.012 \text{ rad} \), what is the minimum permissible length of the bar? (b) If the length of the bar is \( 200 \text{ mm} \), what is the maximum permissible diameter of the bar?