Studies which link the origin of fatigue damage to microscopic deformation processes date back to the work of Ewing & Rosenhain (1900) and Ewing & Humfrey (1903) who reported cracking along traces of active slip planes in fatigued iron. With the invention of electron microscopes, considerable progress has been made in developing a detailed understanding of substructural and microstructural changes induced by cyclic straining. Research work in the past several decades has clearly established the existence of a rich variety of fundamental mechanisms that are specific to cyclic loading conditions. A thorough knowledge of these phenomena is essential for microstructural design for fatigue resistance in engineering materials.

The most conclusive results of deformation mechanisms in fatigue have been obtained on high purity materials, in particular single crystals of face-centered cubic (FCC) metals. In commercial materials, on the other hand, microstructural complexities often preclude clear identification and quantitative treatment of fatigue mechanisms. Cyclic deformation mechanisms in commercial materials are also strongly influenced by processing methods and impurity content.

In this chapter, attention is focused on the mechanisms and micromechanics of deformation in single-crystalline metals and alloys with FCC crystal structures. Also included are brief descriptions of known cyclic-deformation characteristics of bodycentered cubic (BCC) and hexagonal close-packed (HCP) crystals. Cyclic deformation in some rock salt crystals is addressed in Chapter 5.