Stress-strain graph explaination?

[corala]

http://imageshack.us/photo/my-images/812/unledylp.png/


So, A sample of material was stretched and then allowed to contract. A stress-strain graph was obtained as the above picture. Is it true that the material is permanently deformed based on the graph?

And, the gradient of the graph represents either Young's modulus or Shear modulus right? please correct me if I'm wrong.

 

[Studiot]

Look up elastic hysteresis

http://en.wikipedia.org/wiki/Hysteresis#Elastic_hysteresis