The Elastic Plastic Response of a Material

The diagram shows the force displacement
curve for a sample tested in both tension and
compression. At low force and displacement
values the material exhibits an elastic response.
At larger values of (F,u) the material is permanently
deformed, i.e. it has entered the region of Plastic
Deformation.

As indicated on the diagram, the slope of the
elastic region is the same in tension and
compression. In both regions the material obeys Hooke's Law.

From: Ashby & Jones, "Engineering Materials I,"
Pergamon (1986)