A mechanism of fatigue failure

It was shown that when specimens of 2014-T6 aluminum, titanium (6 Al-4 V), and 4130 steel were fatigued, the strength of the surface layer increased. When the strength of this layer reached a critical value, independent of the cyclic stress amplitude a fatigue crack was initiated. The increase in the fatigue life by periodically removing the outer layer of a specimen was investigated under conditions where persistent slip bands or cracks were not present. The results indicate that the increase in fatigue life is associated with a decreased strength of the surface layer resulting from the removal of the high density dislocation layer at the surface.