Stress strain behavior for ductile material

Consider any ductile material, like mild steel bar of uniform cross sections is subjected with uniformly increasing tensile load up to breaking point. It behave differently at different conditions of increasing load.
It's behavior can be easily understood by graphical representation. For this purpose we plot graph stress(σ) vs strain(E). Which is also called as stress strain curve.
If we plot graph as mentioned above it seem like as following.

In above graph we can easily see that, stress strain behavior. In which graph line start form origin after than we obtaints various points which are described as following-
A. Limit of proportionality - Up to this point material obeys Hook's law i.e. stress is directly proportional to the strain. From origin to upto this point(point "A") obtained graph is straight line. From this point straight line start deflect from its direction. From this point material loose its proportional law(i.e. stress is directly proportional to the strain) hence this point is called as "Limit of proportionality(A)."
B. Elastic limit - From point "A" graph deflect form straight line and it become non-liner "A" to "B". Up to point "B" material possese it's elasticity property hence this point called as "Elastic limit(B)." If we remove load applied on material before getting this point material gains its original size and shape.
C. Upper yield point and D. Lower yield point- The state between point "C" and "D" is called as yield state. In this state increase in stain is take place while no increase in stress is occurred. The starting of this state is called as "Upper yield point(C)", while ending of this state is called as "Lower yield point(D)."
E. Ultimate load point - After the yield state stress strain curve increases up to point "E". At this point load(stress) caring capacity of material is maximum hence this point called as "Ultimate load point(E)."
F. Breaking point - After continue loading of material we reach point "F". At this point material fails to carry the load hence this point called as "Failure point(F) or Breaking point(F)."