3.1.4 yield point elongation, YPE—in a uniaxial test, the
strain (expressed in percent) separating the stress-strain curve’s
first point of zero slope from the point of transition from discontinuous yielding to uniform strain hardening. If the
transition occurs over a range of strain, the YPE end point is
the intersection between (a) a horizontal line drawn tangent to
the curve at the last zero slope and ( b) a line drawn tangent to
the strain hardening portion of the stress-strain curve at the
point of inflection. If there is no point at or near the onset of
yielding at which the slope reaches zero, the material has 0 %
YPE.