Abstract
Fatigue test was conducted on a grain-oriented 3% silicon iron under constant amplitude loading. Slip behavior around the fatigue crack tip was observed at the several levels of one loading cycle by means of Atomic Force Microscope (AFM) in order to elucidate the fatigue crack mechanisms. The quantitative evaluation of the fatigue crack growth behavior could be achieved by using the image processing technique. During loading, slips could begin to operate only when the applied stress reached to a certain level. Two preferential slip systems operated at the crack tip in this material. They moved alternately and caused the crack opening and propagation during loading. On the other hand, slips moved in the opposite direction to those during loading at the crack tip alternately and this led the crack closure during unloading. It can be said that the crack open plastically by the slip deformation after it open elastically.
