Yield Strength  Since it is physically difficult in practice to
determine the exact point, (2) where the stress-strain curve
departs from linearity, the point at which an arbitrary offset
drawn parallel to the elastic modulus intersects the stress-
strain curve is defined as the yield point, (3). The yield
strength as commonly applied to copper and copper alloys is the
stress which will produce an extension of either 0.20 percent or
0.50 percent under load. It is known as the Yield Strength at
0.20 percent extension or 0.50 extension. Slightly higher yield
strengths are recorded for the same material using a greater
offset.  Stress Strain Curve