Problem #$1$

F$8-11.$ The material for the $50-mm-$long specimen has the stress$-$strain diagram shown. If $P=150kN$ is applied and then released, determine the permanent elongation of the specimen.Why the area is equals to pi$/4$ x d$^[2]$ is it always eqauls to this $?$

$=\frac{N}{A}=\frac{150({10}^3)}{\frac{}{4}({0\mathrm{.}02}^2)}=\frac{477\mathrm{.}46}{\text{m}\text{p}\text{a}}$

$>{}_{}=450$mpa

$\frac{-0\mathrm{.}00225}{0\mathrm{.}03-0\mathrm{.}00225}=\frac{477\mathrm{.}46-450}{500-450}$

$=0\mathrm{.}0174903$