Properties of Metals
The area between Points 1 and 2 is called the elastic region. If stress is removed,
the material will return to its original length.
Point 2 is the proportional limit (PL) or elastic limit, and Point 3 is the yield
strength (YS) or yield point.
The area between Points 2 and 5 is known as the plastic region because the
material will not return to its original length.
Point 4 is the point of ultimate strength and Point 5 is the fracture point at which
failure of the material occurs.
Figure 3 is a stress-strain curve typical of a
Figure 4 Typical Brittle Material Stress-Strain Curve
ductile material where the strength is small,
and the plastic region is great. The material
will bear more strain (deformation) before
Figure 4 is a stress-strain curve typical of a
brittle material where the plastic region is
small and the strength of the material is high.
The tensile test supplies three descriptive facts
about a material. These are the stress at
which observable plastic deformation or
"yielding" begins; the ultimate tensile strength
or maximum intensity of load that can be
carried in tension; and the percent elongation
or strain (the amount the material will stretch)
and the accompanying percent reduction of
the cross-sectional area caused by stretching.
The rupture or fracture point can also be