$8\mathrm{.}36$ A cold$-$drawn rectangular steel bar of $140$ Bhn is $10$ mm

thick, $60$ mm wide, and has a central hole $12$ mm in

diameter $($as in Figure $4\mathrm{.}40).$ Estimate the maximum ten$-$

sile force that can be applied to the ends and have infi$-$

nite life with $90\%$ reliability and a safety factor of $1\mathrm{.}3$ :

$($a$)$ if the force is completely reversed and $($b$)$ if the force

varies between zero and a maximum value.

$*$Comments $1.$ Bhn can be converted to $)=(1000$ as below.

$S_u=K_B{H}_B$

where $H_B$ is the Brinell hardness number, $K_B$ is a constant of proportionality, and $S_u$ is the tensile

strength in psi. For most steels, $K_B$~~$500.$ Refer to Chap. $3\mathrm{.}6$ of the textbook.