$10/1$ point

A cantilevered stepped circular shaft is made of steel with an ultimate strength of $S_u.$

The shaft is machine surfaced and is subjected to a cyclic torsional load T at its free end as shown. For $d=0\mathrm{.}9in.,$ and the fatigue stress concentration factor $k_f=1\mathrm{.}7,$

if during a typical $30$ seconds of operation the random cyclic torsional load is as shown, determine the resulting torsional shear stress at the fillet at which the number of stress cycle is $3.[$ ksi $]$

$$

$5\mathrm{.}1$