Some aspects of fatigue crack growth retardation behaviour following tensile overloads in a structural steel

The effects of specimen thickness, stress intensity levels and R ratio following single tensile overloads, multiple overloads and overload/underload events have been investigated in a BS4360 Grade 50D steel. The amount of fatigue crack growth retardation increased with both decreasing applied baseline Delta K and increasing overload block size. Smaller increases in retardation were obtained for overload/underload block events compared with block overloads. The data suggests that crack flank plasticity resulting in crack closure adequately accounts for much of the observed behaviour. Near crack tip plasticity was thought to play a more important role in generating crack closure than that remote from the crack tip.