고체역학 (Beer) — Torsion: Problem 3.123

3.123 Using $\tau_{all} = 70 \text{ MPa}$ and $G = 27 \text{ GPa}$, determine for each of the aluminum bars shown the largest torque $T$ that can be applied and the corresponding angle of twist at end $B$. The bars have the following cross-sections and common length: (a) Square cross-section: $25 \text{ mm} \times 25 \text{ mm}$ (b) Rectangular cross-section: $45 \text{ mm} \times 15 \text{ mm}$ Common length $L = 900 \text{ mm}$