The nucleation of cracks in high and low strain metal fatigue

The thesis reviews the literature concerning the high- and low-strain fatigue which is pertinent to the nucleation of cracks during cyclic stressing. The methods of investigating the crack nucleation process are discussed with the disadvantages of each method stated. The thesis deals mainly with the examination of the cracks by surface replication and electron microscopy. A direct carbon replica technique is described which allows the results of macroscopic as well as microscopic deformation to be followed during both low and high strain fatigue. The microscopic deformation (slip) produced an overall macroscopic deformation producing an undulating surface topography with accompanying grain rotations and displacements. The stereoscopic electron micrographs prepared from OFHC copper subjected to fatigue at room temperature have shown that the grain boundaries slip at their common interface at the surface when subjected to a cyclic shear strain. [Continues.]