고체역학 (Gere) — Stresses in Beams (Basic Topics): Problem 5.4-2

5.4-2 A copper wire having a diameter of \( d = 4 \text{ mm} \) is bent into a circle and held with the ends just touching (see figure). (a) If the maximum permissible strain in the copper is \( \epsilon_{\text{max}} = 0.0024 \), what is the shortest length \( L \) of wire that can be used? (b) If \( L = 5.5 \text{ m} \), what is the maximum acceptable diameter of the wire if the maximum normal strain must remain below yield? Assume \( E = 120 \text{ GPa} \) and \( \sigma_Y = 300 \text{ MPa} \).