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.

Many scientific-technological advances depend critically on solid-state elastic properties, their magnitudes, and their responses to variables like stress and temperature. This chapter provides the definitions and descriptions of elastic constants and emphasizes five aspects of engineering-material solid-state elastic constants: general properties; interrelationships; relationships, especially thermodynamic to other physical properties; changes during cooling from ambient to near-zero temperature; and near-zero-temperature behavior.

Specific heat is a fundamental property that relates the total heat per unit mass added to a system to the resultant temperature change of the system. This chapter begins with the definition and historical development of specific heat. Thermodynamic and solid state relationships are presented which include discussions about lattice specific heat and the effects of magnetic and superconducting transitions. Data sources for practical applications and methods of estimating specific heat for materials are also included. The chapter concludes with a section concerning the measurement of specific heat at low temperatures.

Specific heat and thermal expansion are closely related. Following a discussion on thermal expansion theory, methods of measurement techniques are presented along with their advantages and disadvantages. The results of the measurements are then summarized for three classes of materials: metallics, nonmetallics, and composites. Because predicting thermal expansion values for unmeasured or novel materials is useful, the chapter also describes the means of making educated guesses for low-temperature values. A short discussion on how thermal expansion data can be used is followed by a section describing where such data can be found.

This chapter presents basic principles and the theoretical results of heat transport in solids. Thermal conductivity and thermal diffusivity are the principal properties discussed. Discussions are also included on the effects of temperature, magnetic field, and metallurgical variations caused by composition, processing, and heat-treatment differences. Numerous graphs illustrate the qualitative and quantitative effects of these variables. Measurement methods and associated accuracies and pertinent empirical correlations are presented.

This chapter presents topics pertaining to resistance at cryogenic temperatures: measurement, the resistive mechanisms, and available data. The chapter also presents brief descriptions of the various mechanisms that are operative in producing resistance at low temperatures. The alloys discussed are the nondilute mixtures of metals. An introduction to low-temperature electrical properties of specific metals and alloys is included.

This chapter provides a view of magnetism in materials used at low temperatures. The discussion covers the concepts, definitions, and systems of units that are unique to the study of magnetic properties. The chapter provides a description of some of the techniques and devices used for determining magnetic properties.

The mechanical properties of a material describe the relations between the stresses acting on the material and its resulting deformations. Stresses capable of producing permanent deformations, which remain after the stresses are removed, are considered in this chapter. The effects of cryogenic temperatures on the mechanical properties of metals and alloys are reviewed in this chapter; the effects on polymers and glasses are discussed briefly. The fundamental mechanisms controlling temperature-dependent mechanical behavior, phenomena encountered in low-temperature testing, and the mechanical properties of some representative engineering metals and alloys are described. Modifications of test procedures for low temperatures and sources of data are also included.

This chapter reviews the concepts of fracture mechanics and their application to materials evaluation and the design of cryogenic structures. Emphasis is placed on an explanation of technology, a review of fracture mechanics testing methods, and a discussion on the many factors contributing to the fracture behavior of materials at cryogenic temperatures. Three approaches of elastic-plastic fracture mechanics are covered, namely the crack opening displacement, the J-integral, and the R-curve methods. The chapter also discusses the influence of thermal and metallurgical effects on toughness at low temperatures.

This chapter concentrates on very low-temperature martensitic transformations, which are of great concern for cryogenic applications and research. The principal transformation characteristics are reviewed and then elaborated. The material classes or alloy systems that exhibit martensitic transformations at very low temperatures are discussed. In particular, the martensitic transformations and their effects in austenitic stainless steels, iron-nickel alloys, practical superconductors, alkali metals, solidified gases, and polymers are discussed.

This chapter discusses the compatibility problems that arise from chemical or physical interactions between liquefied gases and the common materials used in their production, storage, transportation, distribution, and use. The discussion covers the compatibility of materials with liquid oxygen and liquid fluorine. Hydrogen-environment embrittlement is unique to low-temperature hydrogen systems and is also discussed.

This chapter discusses the structural alloys being used for cryogenic applications in commercially significant quantities. It emphasizes the practical considerations involved in the material selection process and provides the information necessary to make preliminary selections of alloys most suitable for the intended cryogenic application. The chapter provides general information on a class or group of alloys, their representative mechanical and physical properties, and their fabrication characteristics. The materials covered are austenitic stainless steels, nickel steels, aluminum alloys, and other metals and alloys.

Composite systems for cryogenic applications are discussed in this chapter. This chapter emphasizes filamentary-reinforced composites because they are the most widely used composite materials. It begins with a discussion on the approach to designing and fabricating with low-pressure laminate composites. This is followed by a section providing an overview of the materials in modern cryogenic technology. Then, the chapter describes the effect of cryogenic temperatures on materials properties; it also introduces the various joining techniques developed for composite materials. The effects of radiation on the properties of the materials are covered as well as the processes involved in testing laminates at cryogenic temperatures. Finally, the chapter provides information available on concrete aggregate composites.

The chapter presents an overview of the properties and operational limits of superconductive materials, as well as techniques used to fabricate practical superconducting wires. It introduces six properties: critical temperature, critical magnetic field, critical current density, stability, ac loss, and mechanical characteristics; for each property, typical data are provided and the experimental methods used to measure it are briefly described. The properties of the superconducting composites are tied together in the chapter to summarize their effect on superconductor material selection and the geometrical design of superconducting composites. The chapter also contains a reference guide to composite-design factors with links to the relevant chapter sections where each design consideration is addressed.