$$\begin{array}{l}{\text { Data: } P=25 k N, \quad \sigma=110 N / m m^{2}, E=2.1 \times 10^{5} \mathrm{N} / \mathrm{mm}^{2}} \ {\text { Find: } d_{\min }} \ {\sigma=\frac{p}{A}=\frac{P}{\left(\frac{\pi \mathrm{d}^{2}}{4}\right)}}\end{array}$$ $$\begin{array}{l}{\mathrm{d}^{2}=\frac{\mathrm{P}}{\left(\frac{\pi \sigma}{4}\right)}} \ {\mathrm{d}=\sqrt{\frac{\mathrm{P}}{\left(\frac{\pi \sigma}{4}\right)}}} \ {\mathrm{d}=\sqrt{\frac{25 \times 10^{3}}{4}}} \ {\mathrm{d}=17.84 \mathrm{mm}}\end{array}$$