$13-1.$ Define a homogeneous material.

$13-2.$ Indicate the points on the stress$-$strain igram which

represent the proportional limit and the ultimate stress.

Prob. I$3-2$

$18-3.$ Define the modulus of elasticity $E.$

F$3-4.$ At room temperature, mild steel is a ductile material.

True or false?

$13-5.$ Engineering stress and strain are calculated using

the actual cross$-$sectional area and gage length of the

specimen. True or false?

F$3-6.$ As the temperature increases the modulus of

elasticity will increase. True or false?

$13-7.$ A $100-mm-$long rod has a diameter of $15$ mm $.$ If an

axial tensile load of $100$ kN is applied, determine its change

in length. Assume linear elastic behavior with $E=200$GPa.

$173-8.$ A bar has a length of $8$ in $.$ and cross$-$sectional area of

$12i{n}^2.$ Determine the modulus of elasticity of the material if

it is subjected to an axial tensile load of $10$ kip and stretches

$0\mathrm{.}003$ in $.$ The material has linear elastic behavior.