Fig. P$1\mathrm{.}1$ and P$1\mathrm{.}2$

$1\mathrm{.}2$ Two solid cylindrical rods $AB$ and $BC$ are welded together at $B$ and

loaded as shown. Knowing that the average normal stress must not

exceed $150$ MPa in either rod, determine the smallest allowable val$-$

ues of the diameters $d_1$ and $d_2.$