This chapter explains why it is sometimes necessary to separate inelastic from elastic strains and how to do it using one of two methods. It first discusses the direct calculation of strain-range components from experimental data associated with large strains. It then explains how the method can be extended to the treatment of very low inelastic strains by adjusting tensile and compressive hold periods and continuous cycling frequencies. The chapter then begins the presentation of the second approach, called the total strain-range method, so named because it combines elastic and inelastic strain into a total strain range. The discussion covers important features, procedures, and correlations as well as the use of models and the steps involved in predicting thermomechanical fatigue (TMF) life. It also includes information on isothermal fatigue, bithermal creep-fatigue testing, and the predictability of the method for TMF cycling.

This chapter compares and contrasts the high-temperature behaviors of metals and composites. It describes the use of creep curves and stress-rupture testing along with the underlying mechanisms in creep deformation and elevated-temperature fracture. It also discusses creep-life prediction and related design methods and some of the factors involved in high-temperature fatigue, including creep-fatigue interaction and thermomechanical damage.

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.

Fiber-reinforced metal-matrix composites have carved out a niche in applications requiring high strength to weight ratios, but they are susceptible to failure when exposed to high temperatures and cyclic loads. This chapter discusses the obstacles that must be overcome to improve the creep-fatigue behavior of these otherwise promising materials. It addresses six areas that have been the focus of intense research, including thermal-expansion and elastic-viscoplastic mismatch, thermally induced biaxiality and interply stresses, creep and cyclic relaxation of residual stresses, and enhanced interfaces for oxidation.

This chapter provides a detailed review of creep-fatigue analysis techniques, including the 10% rule, strain-range partitioning, several variants of the frequency-modified life equation, damage assessment based on tensile hysteresis energy, the OCTF (oxidation, creep, and thermomechanical fatigue) damage model, and numerous methods that make use of creep-rupture, crack-growth, and void-growth data. It also discusses the use of continuum damage mechanics and includes examples demonstrating the accuracy of each method as well as the procedures involved.

This chapter discusses the processes of isothermal and hot-die forging and their use in producing aerospace components. It explains how isothermal forging was developed to provide a near-net shape component geometry and well-controlled microstructures and properties with accurate control of the working temperature and strain rate. It describes the materials typically used as well as equipment and tooling, die heating procedures, part separation techniques, and postforging heat treatment.

Combustion turbines consist of a compressor, a combustor, and a turbine. As commonly configured, the compressor and turbine mount on a single shaft that connects directly to a generator. This chapter reviews the materials of construction, damage mechanisms, and life-assessment techniques for nozzles and buckets. It also presents key information from a detailed review of the literature and the results of a survey on combustion-turbine material problems.

This chapter provides practical information on the forming and forging processes used to manufacture titanium parts, including die forging, precision die forging, hot and cold forming, superplastic forming, and deep drawing. It explains how process variables such as temperature, pressure, and strain rate influence microstructure and properties and provides recommended ranges for commonly formed and forged titanium alloys.

This chapter explains how the authors assessed the potential risks of creep-fatigue in several aerospace applications using the tools and techniques presented in earlier chapters. It begins by identifying the fatigue regimes encountered in the main engines of the Space Shuttle. It then describes the types of damage observed in engine components and the methods used to mitigate problems. It also discusses the results of analyses that led to changes in design or approach and examines fatigue-related issues in turbine engines used in commercial aircraft.

Unlike conventional quench and temper heat treatment, austempering is an iron and steel heat-treatment process that enhances mechanical properties through the isothermal transformation of austenite with a minimum amount of quenching stresses. This chapter begins with a discussion of austemperability requirements. Then outlines of austenitizing and austempering cycles and resultant microstructures are presented. This is followed by sections discussing the mechanical properties, advantages, limitations, machinability, process variants, and applications of austempered ductile iron (ADI). Information on the growth of premachined ADI components is also provided. Further, the chapter describes two slightly different systems for austempering: atmospheric-salt and salt-salt systems. Finally, it presents general guidelines for component designers, casting manufacturers, and heat treaters to apply ADI more widely and with improved success.

Titanium aluminides are lightweight materials that have relatively high melting points and good high-temperature strength. They also tend to be stronger and lighter than conventional titanium alloys, but considerably less ductile. This chapter begins with a review of the titanium-aluminum phase diagram, focusing on the properties, compositions, and microstructures of alpha-2 Ti3Al alloys. It then describes the properties, microstructures, and compositions of orthorhombic, gamma, and near-gamma alloys as well as the processing methods and procedures normally used in their production.

This chapter discusses the equipment and processes used to convert titanium billet and bar into useful shapes or more refined product forms. These secondary working operations include open-die, closed-die, hot-die and isothermal forging as well as ring rolling and extruding. The chapter describes each method in detail and how it affects the microstructure and mechanical properties of various titanium alloys. It also discusses the propensity of titanium to react with oxygen and hydrogen when heated and explains how to mitigate the effects.