The relationship between intrinsic, closure-free threshold stress
intensity and near-tip residual stress, characterizes the effect of load
magnitude as well as load history on near-threshold fatigue crack growth
rates. It serves as a reference against which precise closure data can
be extracted from growth rates to calibrate analytical estimates. These
possibilities were subjected to rigorous experimental verification
involving threshold and near-threshold fatigue response under overloads,
underloads with load-shedding on a steel prone to oxide debris
formation. The study reveals why conventional load shedding practice to
characterize threshold stress intensity is prone to yield unconservative
and misleading results.