고체역학 (Beer) — Torsion: Problem 3.89

3.89 A torque of magnitude $T = 200 \text{ lb}\cdot\text{in.}$ is applied to the stepped shaft shown, which has a full quarter-circular fillet. Knowing that $D = 1 \text{ in.}$, determine the maximum shearing stress in the shaft when (a) $d = 0.8 \text{ in.}$, (b) $d = 0.9 \text{ in.}$