Q$4.[0\mathrm{.}6\backslash \%]$

A $80$ Nm couple is applied to the steel bar.

$($a$)$ Assuming that the couple is applied about the $\backslash ($ z $\backslash )$ axis as shown, determine the maximum stress and the radius of curvature of the bar.

$($b$)$ Solve part $($a$)$ again assuming that the couple is applied about the $\backslash ($ y $\backslash )$ axis instead.

Use $\backslash (\backslash$mathrm$\{$E$\}=200\backslash$mathrm$\{$GPa$\}\backslash )$ for this question.