Formation of fatigue cracks

Abstract

The contours of the slip bands produced by fátigue straining of metals are viewed by a process of taper-seotioning and optical microscopy which permits effective magnifications of some 20000 times. The observations indicate ways in which the slip bands may turn into cracks and start disintegration of the metal surface. They also show that the mechanism of deformation and failure changes as the amplitude of the cyclic straining increases, the general form of the fatigue SIN curve arising from auperposition of two distinct mechanisms. The observations support the view that fatigue craoking is primerily a simple geometrical consequence of to-and-fro fine slip movements in the fatigue slip-bands.