After this limit has been exceeded, the size and shape of the specimen after removal of the load will not be the same as before, and the difference or amount of change is known as the ~permanent set~.
Elastic limit as measured in tests and used in design may be defined as that unit stress at which the deformation begins to increase in a faster ratio than the applied load.

In practice the elastic limit of a material under test is determined from the stress-strain diagram.

It is that point in the line where the diagram begins perceptibly to curve.[2] (See Fig.

1.) [Footnote 2: If the straight portion does not pass through the origin, a parallel line should be drawn through the origin, and the load at elastic limit taken from this line.

(See Fig.