Comparing materials using measured data

$[20$ pts$]$

The table below shows data collected for two materials: poly$($ethylene$)$ and poly

$($tetrafluoroethylene$).$

A$.$ Plot the stress$-$strain curves for both materials with x$,$y axis labels and units. Then

calculate the Young's Modulus $($E$)$ for each material. Show both materials on the same

plot to allow easy comparison. $(5$ pts$)$

Hints: Calculate E for each material by using the linear region of each plot. This is

the elastic region in the notes. Do not use the plastic region for calculation of E$.$

Please remember, YM is one number for each material and not a series of numbers.

B$.$ Using the graph from part A$,$ for each material determine the approximate strain energy

before plastic deformation begins. $(5$ pts$)$

Hint: Display U$\_(0)$ calculations in MPa. Choose a stress value that is in the linear

region for both the plots. Draw a straight line parallel to x $-$axis that crosses the linear

section of both the plots. Use the corresponding stress and strain values to calculate strain

energy. You can always use the table to get the exact strain values from linear region, if

needed.

C$.$ Compare the Young's Moduli and strain energies for both materials. What do these

calculations tell us about the properties of these materials? $(2$ pts$)$

Assume $2$ materials have Young's moduli of $30,000,$ and $10000$ MPa $,$ respectively. $(20$ pts$)$

A$.$ How much strain energy is required to deform each to a strain of $0\mathrm{.}1\%?$

B$.$ How much strain energy is stored in each, if they are exposed to stress of $30$ MPa $?$

C$.$ Which is the most brittle, and which is the most complaint material?