Fatigue failures occur due to the application of fluctuating stresses that are much lower than the stress required to cause failure during a single application of stress. This chapter describes three basic factors that cause fatigue: a maximum tensile stress of sufficiently high value, a large enough variation or fluctuation in the applied stress, and a sufficiently large number of cycles of the applied stress. The discussion covers high-cycle fatigue, low-cycle fatigue, and fatigue crack propagation. The chapter then discusses the stages where fatigue crack nucleation and growth occurs. It describes the most effective methods of improving fatigue life. The chapter also explains the effect of geometrical stress concentrations on fatigue. In addition, it explores the environmental effects of corrosion fatigue, low-temperature fatigue, high-temperature fatigue, and thermal fatigue. Finally, the chapter discusses a number of design philosophies or methodologies to deal with design against fatigue failures.

This chapter focuses on the processes and mechanisms involved in fatigue. It begins with a review of some of the early theories of fatigue and the tools subsequently used to obtain a better understanding of the fatigue process. It then explains how plasticity plays a major role in creating dislocations, breaking up grains into subgrains, and causing microscopic imperfections to coalesce into larger flaws. It also discusses the factors that contribute to the development and propagation of fatigue cracks, including surface deterioration, volumetric and environmental effects, foreign particles, and stresses generated by rolling contact.

This chapter discusses the effect of fatigue on polymers, ceramics, composites, and bone. It begins with a general comparison of polymers and metals, noting important differences in microstructure and cyclic loading response. It then presents the results of several studies that shed light on the fatigue behavior and crack growth mechanisms of common structural polymers and moves on from there to discuss the fatigue behavior of bone and how it compares to stable and cyclically softening metals. It also discusses the fatigue characteristics of engineered and composited ceramics and ceramic fiber-reinforced metal-matrix composites.

Structural and fracture mechanics-based tools for metals are believed to be applicable to nonmetals, as long as they are homogeneous and isotropic. This chapter discusses the essential aspects of the fatigue and fracture behaviors of nonmetallic materials with an emphasis on how they compare with metals. It begins by describing the fracture characteristics of ceramics and glasses along with typical properties and subcritical crack growth mechanisms. It then discusses the properties of engineering plastics and the factors affecting crack formation and growth, fracture toughness, fatigue life, and stress rupture failures.

This appendix presents an analytical model that estimates damage rates for both crack initiation and propagation mechanisms. The model provides a nonarbitrary definition of fatigue crack initiation length, which serves as an analytical link between initiation and propagation analyses and appears to have considerable merit in estimating the total fatigue life of notched and cracked structures.

This article is a detailed account of the mechanisms of fatigue failure of polymers, namely thermal fatigue failure and mechanical fatigue failure. The mechanical fatigue failure is discussed in terms of fatigue crack initiation and fatigue crack propagation.

This chapter describes the phenomenological aspects of fatigue and how to assess its effect on the life of components operating in high-temperature environments. It explains how fatigue is measured and expressed and how it is affected by loading conditions (stress cycles, amplitude, and frequency) and factors such as temperature, material defects, component geometry, and processing history. It provides a detailed overview of the damage mechanisms associated with high-cycle and low-cycle fatigue as well as thermal fatigue, creep-fatigue, and fatigue-crack growth. It also demonstrates the use of tools and techniques that have been developed to quantify fatigue-related damage and its effect on the remaining life of components.