Describe the behaviour of a wire under gradually increasing load?

Let us consider a wire suspended from a rigid support and a load is applied at other end of
the wire. The load gradually increases, the graph drawn between strain along x-axis and
stress along y-axis. 
1. Proportional Limit (A) : Upto A stress is directly proportional to strain, OA is straight
line, the wire obeys hooks law OA is called proportional limit.
2. Elastic Limit (B): From A to B the stress is further increased the wire does not obey hooks Law. But elastic nature of the wire will exist upto B. If the wire unloaded the wire regains its original length.

3. Yield point (C ): If the stress further increased beyond B, then yielding starts, the starting point of yielding is called yield point.
4. Permanent set (OP): If the stress decreased between B and D points, the wire cannot regain its original length, that means the length of the wire permanently increased. It is denoted by ‘OP’
5. Breaking point E : The thickness of the wire decreases and finally breaks at point E, the point E is called breaking point.