고체역학 (Beer) — Stress and Strain—Axial Loading: Problem 2.107

2.107 Rod $AB$ consists of two cylindrical portions $AC$ and $BC$, each with a cross-sectional area of $1750\text{ mm}^2$. Portion $AC$ is made of a mild steel with $E = 200\text{ GPa}$ and $\sigma_Y = 250\text{ MPa}$, and portion $BC$ is made of a high-strength steel with $E = 200\text{ GPa}$ and $\sigma_Y = 345\text{ MPa}$. A load $P$ is applied at $C$ as shown. Assuming both steels to be elastoplastic, determine (a) the maximum deflection of $C$ if $P$ is gradually increased from zero to $975\text{ kN}$ and then reduced back to zero, (b) the maximum stress in each portion of the rod, (c) the permanent deflection of $C$.