Strain-range partitioning is a method for assessing the effects of creep fatigue based on inelastic strain paths or strain reversals. The first part of the chapter defines four distinct strain paths that can be used to model any cyclic loading pattern and describes the microstructural damages associated with each of the four basic loading cycles. The discussion then turns to fatigue life prediction for different types of materials and more realistic loading conditions, particularly those in which hysteresis loops have more than one strain-range component. To that end, the chapter considers two cases. In one, the relationship between strain range and cyclic life is established from test data. In the other, a rule is required to determine the damage of each concurrent strain and the total damage of the cycle is used to predict creep-fatigue life. The chapter presents several such damage rules and discusses their applicability in different situations.

This chapter demonstrates the versatility of the strain-range partitioning method and its application to creep-fatigue problems involving complex loading histories. It begins with a derivation showing that it is possible to assess the damage of hysteresis loops combining two or more strain ranges using generic loops based on fundamental data. It then explains how to treat problems involving sequential loading with both healing and damage cycles and presents a general solution for combining two loops with arbitrary amounts of the four strain-range components. The chapter also derives closed-form equations that account for interactions among any number of adjacent loops and can be used, through successive application, to analyze any loading history.

This chapter addresses the question of how to deal with multiaxial stresses and strains when using the strain-range partitioning method to analyze the effects of creep fatigue. It is divided into three sections: a general discussion on the rationale used in formulating rules for treating multiaxiality, a concise listing of the rules, and an example problem in which axial creep-fatigue data is used to predict the torsional creep-fatigue life of type 304 and 316 stainless steel. The chapter also includes a brief introduction in which the authors outline the challenges presented by multiaxial loading and set practical limits on the problem they intend to treat.

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 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 compares and contrasts empirical approaches for partitioning hysteresis loops and predicting creep-fatigue life. The first part of the chapter presents experimental partitioning methods, explaining how they can be used to partition any loading cycle into its basic strain-range components. The methods covered include rapid cycling between peak stress extremes, half-cycle rapid loading and unloading, and variations of the incremental step-stress approach. The methods are then compared based on their ability to predict creep-fatigue life. The chapter goes on from there to describe how fatigue life can be estimated from ductility measurements when cyclic data are unavailable or are likely to change. It also explains how cyclic life is influenced by the time-dependent nature of creep-plasticity and the physical and metallurgical effects of environmental exposure.

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.

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.

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 addresses the cumulative effects of fatigue and how to determine its impact on component lifetime and performance. It begins by defining a loading history and its corresponding hysteresis loops that exposes the deficiencies of some of the theories discussed. It then proceeds to demonstrate the methods commonly used to analyze cumulative fatigue damage and its effect on component life starting with the classical linear damage rule. After pointing out the inherent limitations of the model, it presents a method that incorporates two linear damage rules, one applying prior to crack initiation and the other after the crack has started. Although the method accounts somewhat better for loading-order effects, the transition in behavior that the rules presume to model occurs prior to any signs of cracking. Two modified versions of the double linear damage rule method, neither of which are related to a physical crack initiation event, are subsequently presented along with several applications showing how the different methods compare. The examples provided include two-level and multilevel tests, a gas-turbine engine compressor disk, and the cumulative damage associated with the irreversible hardening of type 304 stainless steel.

This article briefly reviews abrasive and adhesive wear failure of reinforced polymers and polymer composites, namely particulate-filled polymers, short-fiber-reinforced polymers, polymers with continuous fibers, and mixed reinforcements and fabrics. It includes scanning electron microscope micrographs of abraded surfaces of composites against 80-grade SiC paper and under 14 N load, and worn surfaces of abraded polyether-imide composites and polyamide 66 unidirectional composites and 66 hybrid composites.

This chapter discusses some of the methods and measurements used to construct phase diagrams. It explains how cooling curves were widely used to determine phase boundaries, and how equilibrated alloys examined under controlled heating and cooling provide information for constructing isothermal and vertical sections as well as liquid projections. It also explains how diffusion couples provide a window into local equilibria and identifies typical phase diagram construction errors along with problems stemming from phase-boundary curvatures and congruent transformations.

This chapter examines the stress-strain characteristics of metals and alloys subjected to cyclic loading and the cumulative effects of fatigue. It begins by explaining how a single load reversal can lower the yield stress of a material and how repeated reversals can cause strain hardening and softening, both of which lead to premature failure. It then discusses the stages of fatigue fracture, using detailed images to show how cracks initiate and grow and how they leave telltale marks on fracture surfaces. It goes on to describe fatigue life assessment methods and demonstrate their use on different metals and alloys. The chapter also discusses design-based approaches for preventing fatigue failures.

This chapter provides a detailed overview of the creep behavior of metals and how to account for it when determining the remaining service life of components. It begins with a review of creep curves, explaining how they are plotted and what they reveal about the operating history, damage mechanisms, and structural integrity of the test sample. In the sections that follow, it discusses the effects of stress and temperature on creep rate, the difference between diffusional and dislocation creep, and the use of time-temperature-stress parameters for data extrapolation. It explains how to deal with time dependent deformation in design, how to estimate cumulative damage under changing conditions, and how to assess the effect of multiaxial stress based on uniaxial test data. It also includes information on rupture ductility, creep fracture, and creep-crack growth and their effect on component life and performance.

This chapter discusses the failure mechanisms associated with fiber-reinforced composites. It begins with a review of fiber-matrix systems and the stress-strain response of unidirectional lamina and both notched and unnotched composite laminate specimens. It then explains how cyclic loading can lead to delamination, the primary failure mode of most composites, and describes some of the methods that have been developed to improve delamination resistance, assess damage tolerance, determine residual strength, and predict failure modes.

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 covers the failure modes and mechanisms of concern in steam turbines and the methods used to assess remaining component life. It provides a detailed overview of the design considerations, material requirements, damage mechanisms, and remaining-life-assessment methods for the most-failure prone components beginning with rotors and continuing on to casings, blades, nozzles, and high-temperature bolts. The chapter makes extensive use of images, diagrams, data plots, and tables and includes step-by-step instructions where relevant.

Creep occurs in any metal or alloy at a temperature where atoms become sufficiently mobile to allow the time-dependent rearrangement of structure. This chapter begins with a section on creep curves, covering the three distinct stages: primary, secondary, and tertiary. It then provides information on the stress-rupture test used to measure the time it takes for a metal to fail at a given stress at elevated temperature. The major classes of creep mechanism, namely Nabarro-Herring creep and Coble creep, are then covered. The chapter also provides information on three primary modes of elevated fracture, namely, rupture, transgranular fracture, and intergranular fracture. The next section focuses on some of the metallurgical instabilities caused by overaging, intermetallic phase precipitation, and carbide reactions. Subsequent sections address creep life prediction and creep-fatigue interaction and the approaches to design against creep.

This chapter discusses the use of mechanical fastening and adhesive bonding, the primary methods for joining polymer matrix composites. It describes and analyzes the basic types of mechanically fastened joints, including single-hole and multirow bolted composite joints. It then reviews the advantages and disadvantages of adhesively bonded joints and compares and contrasts the long-term performance of various joint designs. The chapter also discusses the merits of stepped-lap and bonded-bolted joints.

This chapter is a detailed account of various attributes related to mixing and testing of powder-binder feedstocks. Mixing parameters and their effects on feedstock properties is discussed. The attributes reviewed include mixture homogeneity, wetting, powder-binder ratio, feedstock density, elastic modulus, rheological behavior, particle size, formulation control, feedstock mixing, and feedstock properties. The chapter also provides information on the processes involved in feedstock preparation and testing.