Elasticity
Since we can determine stress and strain for different loads, if we were to plot a graph of stress versus strain, we would obtain a curve similar to the one in the diagram.
Notice that there is a portion of the curve that is linear; that is, a straight line. This straight portion of the curve is called the elastic range.
As long as the stress in the rod does not exceed the elastic limit, the rod returns to its original shape after the force is removed.
The elastic limit for any particular material is that point on the stress-strain diagram where the relationship between stress and strain is no longer linear.
In the diagram, the elastic or proportional limit is labeled as point A.