고체역학 (Beer) — Principal Stresses Under a Given Loading: Problem 8.18

8.18 The 4-kN force is parallel to the \(x\) axis, and the force \(Q\) is parallel to the \(z\) axis. The shaft \(AD\) is hollow. Knowing that the inner diameter is half the outer diameter and that \(\tau_{\text{all}} = 60 \text{ MPa}\), determine the smallest permissible outer diameter of the shaft.