Question $1$

$4\mathrm{.}13$ Estimate the plastic work necessary to stretch a tensile specimen $($initial area $A=$

$35\mathrm{.}8m{m}^2$ and initial length $l_1=50\mathrm{.}8mm)$ to instability when it is assumed that

the material can be described by $\frac{?}{\text{b}\text{a}\text{r}}()=\frac{1200}{b}ar(lon{)}^{-0\mathrm{.}35}\frac{N}{m}{m}^2.$

Question $2$

$4\mathrm{.}14$ A thin$-$walled sphere $(D_1=750mm,t=1mm)$ is expanded by internal pressure

to a diameter of $D_2=850mm.$ Determine the plastic work necessary. The ma$-$

terial can be described by the expression $\frac{?}{\text{b}\text{a}\text{r}}()=\frac{1200}{b}ar(lon{)}^{-0\mathrm{.}35}\frac{N}{m}{m}^2.$

Question $3$

$15$ A cylindrical specimen $D_1=30mm,h_1=20mm$ is plastically deformed to

$h_2=\frac{j}{j}{h}_1.$ The material can be described by $\frac{?}{\text{b}\text{a}\text{r}}()=\frac{160}{b}ar(lon{)}^{-0\mathrm{.}23}\frac{N}{m}{m}^2.$ Determine:

a$.$ The true stress at the end of the deformation

b$.$ The nominal stress at the end of the deformation

c$.$ The plastic work necessary