Theory of the fatigue of metals

Abstract

The most striking features of fatigue phenomena are: (1) The quasi-brittle nature of fatigue fracture. A metal, however ductile, can break in a fatigue test without any appreciable external deformation, like a brittle material. A further similarity to brittle fracture is that fine cracks and other faults, which would not influence noticeably the static strength of a ductile material, substantially impair its fatigue endurance. (2) Internal distortions . In spite of the possible absence of any external deformation, heavy local distortions can be observed microscopically on a material subjected to a fatigue test (Ewing and Humfrey 1903). The evidence for internal distortions has been extended by the X-ray work of Gough and his collaborators (Gough 1933; Gough and Wood 1936, 1938 a , 1938 b ) who found that X-ray photographs of fatigue-fractured metals show, in the immediate neighbourhood of the fatigue crack, qualitatively and quantitatively the same alterations as those of metals fractured in static tests.