Changes in lattice-strain profiles around a fatigue crack through the retardation period after overloading

An overload was applied during a fatigue-crack-growth experiment, resulting in a temporary decrease in crack-growth rates, i.e., a retardation period. Neutron diffraction was used to investigate the retardation phenomenon by mapping the changes in the lattice-strain profiles around the fatigue-crack tip in a series of compact-tension (CT) specimens, which were fatigued to various stages through the retardation period after the overload. Following the overload, compressive-strain fields were observed along the loading direction close to the crack tip. As the crack grows out of the retardation period, the residual compressive strains decreased.