Please find below some experimental data taken from a peer$-$reviewed research article on electrospun nanofibers made from a novel PLGA structure. These fibers were spun into a mesh from which rectangular samples were cut and placed into a tensile test machine. Below are examples of three stress versus strain curves, pulled to mechanical failure.

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Where does the transition from elastic to plastic deformation occur in this polymer? Why did you come to that conclusion?

Based on that transition point, what is your estimate for the Young's modulus of this material?

What is your estimate for the ultimate tensile strength of this material?

Based only on the stress versus strain curve provided above, do you know if this material is elastic, viscoelastic, or a viscous liquid? Why or why not?