Microscopic analysis of non-propagating fatigue crack tips

Herein, the phenomena around a non-propagating fatigue crack tip in polycrystalline interstitial-free steel were investigated on a microscopic scale. A non-propagating fatigue crack was introduced in a standard compact tension specimen using a load-shedding procedure. The near-tip area was subsequently investigated via scanning electron microscopy and transmission electron microscopy. The wake in the tip area was covered with an oxide layer. Discrete dislocations, whose densities were relatively low, were only found in front of the crack. These results may suggest that an increase of the opening point was attributable to the oxide-induced crack closure rather than the plasticity-induced one.