This chapter provides a quantitative treatment of the cracking mechanisms associated with fatigue, drawing on the principles of fracture mechanics. It explains that although fracture mechanics originated with the aim of understanding sudden and catastrophic crack extension, the main premise of a stress field in the vicinity of the crack also applies to the study of cycle-by-cycle stable crack growth. A detailed review is given of the many developments and discoveries that helped shape the theory and methods collectively defined as crack mechanics, which the authors then employ to analyze the crack growth behavior of various materials, including steels and nonferrous alloys, under constant-amplitude loading. The authors then deal with the effects of complex loading using crack retardation and crack closure models to show how load fluctuations can slow crack growth rates and even cause total crack arrest. They also present the results of a study on crack initiation, propagation, and fracture in circular (rather than rectangular) specimens and a fatigue study on ductile and quasi-brittle materials.

Temperature and deformation gradients developed in the course of manufacturing can have undesired effects on the microstructures along their path; the two most common being residual stress and distortion. This chapter discusses these manufacturing-related problems and how they can be minimized by heat treatments. It also provides information on residual stress evaluation and prediction techniques.

Fracture mechanics is a well-developed quantitative approach to the study of failures. This chapter discusses fracture toughness and fracture mechanics, linear-elastic fracture mechanics, and modes of loading. The discussion also covers plane strain and stress and crack growth kinetics. The chapter presents a case history that illustrates the use of fracture mechanics in failure analysis. An appendix provides a more detailed discussion of fracture mechanics concepts.

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 chapter presents an overview of some of the major causes of tool and die failures. The chapter describes fracture and fracture toughness of tool steels, and the influence of factors such as steel quality and primary processing, mechanical design, heat treatment, grinding and finishing, and distortion and dimensional change.

This article discusses the various options for controlling fatigue and fracture in welded steel structures, the factors that influence them the most, and some of the leading codes and standards for designing against these failure mechanisms. The two most widely used approaches discussed for fatigue control in welded joints are the S-N curve approach and the fracture mechanics assessment methods.

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 article discusses various factors influencing general polymeric behavior, ductile-brittle transitions, crazing, and the brittle fracture of polymeric materials. The discussion covers the effects of environment on glassy thermoplastic, several parametric descriptions of craze initiation, the kinetics of craze growth, and the effect of crazing on toughness of the plastic. In addition, the article provides information on various tests to determine stress-to-craze value, strain-to-craze value, and fracture toughness of the plastic.

This chapter discusses various types of material fracture toughness and the methods by which they are determined. It begins with a review of the basic principles of linear elastic fracture mechanics, covering the Griffith-Irwin theory of fracture, the concept of strain energy release rate, the use of fracture indices and failure criteria, and the ramifications of crack-tip plasticity in ductile and brittle fractures. It goes on to describe the different types of plain-strain and plane-stress fracture toughness, explaining how they are measured and how they are influenced by metallurgical and environmental variables and loading conditions. It also examines the crack growth resistance curves of several aluminum alloys and describes the characteristics of fracture when all or some of the applied load is in the plane of the crack.

Fracture mechanics is the science of predicting the load-carrying capabilities of cracked structures based on a mathematical description of the stress field surrounding the crack. The fundamental ideas stem from the work of Griffith, who demonstrated that the strain energy released upon crack extension is the driving force for fracture in a cracked material under load. This chapter provides a summary of Griffith’s work and the subsequent development of linear elastic and elastic-plastic fracture mechanics. It includes detailed illustrations and examples, familiarizing readers with the steps involved in determining strain energy release rates, stress intensity factors, J-integrals, R-curves, and crack tip opening displacement parameters. It also covers fracture toughness testing methods and the effect of measurement variables.

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.

A systematic procedure for minimizing risks involved in heat treated steel components requires a combination of metallurgical failure analysis and fitness for service with respect to safety and reliability based on risk analysis. This chapter begins with an overview of heat treat processing of steels. This is followed by sections on various aspects of heat treatment design and heat treating practices for minimizing distortion. Influence of design, steel grade, and condition is then illustrated in the examples of failures due to heat treatment. A procedure is analyzed to improve the performance of the design process of a component. A heat-transfer model, coupling with a phase transformation model, a thermomechanical model, and a thermochemical model, is also considered. The chapter further provides information on the failure aspects of and heat treatment procedures applied to welded components. It ends with a section on risk-based approach applicable to heat treated steel components.

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.

Depending on the operating environment and the nature of the applied loading, a structure can fail by a number of different modes, including brittle fracture, ductile fracture, plastic collapse, fatigue, creep, corrosion, and buckling. These failure modes can be broken down into the categories of fracture, fatigue, environmental cracking, and high-temperature creep. This article discusses each of these categories, as well as the benefits of a fitness-for-service approach.

This article discusses the material and engineering issues associated with plastic components subjected to impact. The first part covers the effects of loading rate, temperature, and state of stress on both deformation and mode of failure. It discusses standard impact tests, along with their associated results. A brief discussion on the linear elastic fracture mechanics method is presented, along with an example of its effectiveness as a predictive tool for impact performance. Various issues with a bearing on impact performance, such as processing, chemical attack, and aging, are also described. The second part describes the engineering calculations used to predict the performance of thin plastic beams, plates, and shells. The issue of assuming small displacements for the calculation of plastic structure performance is discussed and its limitations described. An example of the consequence of the very low modulus of elasticity associated with plastics and some plastic design solutions are offered.

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.

This chapter addresses the issue of die failures in hot and cold forging operations. It describes failure classifications, fatigue fracture and wear mechanisms, analytical wear models, and the various factors that limit die life. It also includes several case studies in which finite-element modeling is used to predict die failure and extend die life.

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.

As fiber-reinforced polymeric composites continue to be used in more damage-prone environments, it is necessary to understand the response of these materials when subjected to impact from foreign objects. This chapter provides an overview of the analysis methods for impact-damaged composites. It discusses the causes and effects of various failure mechanisms in composite materials. The failure mechanisms covered are brittle-matrix composite failure, tough-matrix composite failure, thermoplastic-matrix composite failure mechanisms, untoughened thermoset-matrix composite failure mechanisms, toughened thermoset-matrix composite failure mechanisms, particle interlayer-toughened composite failure mechanisms, and dispersed-phase, rubber-toughened thermoset-matrix composite failure mechanisms.

This chapter summarizes the performance attributes of advanced high-strength steels, namely stiffness, strength, strain hardening, fatigue, crashworthiness, formability, toughness, and bake hardening.