$4.($partly from Problems $6-2\backslash$& $6-4)$

$(1)$ For the steel$-$material strength data in rows $\backslash ($ a$,$ b $\backslash ),$ assigned in the table below, calculate the uncorrected endurance limit and draw a strength$-$life $($S$-$N$)$ diagram.

$(2)$ For the aluminum$-$material strength data in the rows e$,$ f$,$ assigned in the table below, calculate the uncorrected fatigue strength at $5$E$8$ cycles and draw a strength$-$life $($S$-$N$)$ diagram for the material

$\backslash$begin$\{$tabular$\}\{|$c$|$c$|$c$|\}$

$\backslash$hline Row & $\backslash ($ S$\_\{$u t$\}(\backslash$mathrm$\{$psi$\})\backslash )$ & mat'l $\backslash \backslash$

$\backslash$hline a & $90000$ & steel $\backslash \backslash$

$\backslash$hline b & $250000$ & steel $\backslash \backslash$

$\backslash$hline e & $25000$ & alum. $\backslash \backslash$

$\backslash$hline f & $70000$ & alum. $\backslash \backslash$

$\backslash$hline

$\backslash$end$\{$tabular$\}$