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 provides an outline of the failure modes and mechanisms associated with most boiler tube failures in coal-fired power plants. Primary categories include stress rupture failures, water-side corrosion, fire-side corrosion, fire-side erosion, fatigue, operation failures, and insufficient quality control.

Unlike metals, in which fatigue failures are due to a single crack that grows to a critical length, the effects of fatigue in composites are much more distributed and varied. As the chapter explains, there are five major damage mechanisms that contribute to the progression of composite fatigue, those being matrix cracking, fiber breaking, crack coupling, delamination initiation, and delamination growth. The chapter describes each mechanism in detail along with related factors. It also discusses the primary differences between composites and metals, the effect of manufacturing defects, damage tolerance, and testing and certification.

A low-pressure turbine rotor blade failed during a test run, causing extensive damage to an aircraft engine. Visual examination showed that the nickel-base superalloy blade broke above the root platform in the airfoil section, leaving a fracture surface with two distinct regions, one characteristic of fatigue, the other, overload. Two dents were also visible on the leading edge, near the origin of the fracture. Based on these observations and the results of SEM fractography, investigators concluded that the blade failed due to fatigue aided by cracks in the surface coating caused by mechanical damage.

This chapter provides a brief review of industry’s battle with fatigue and fracture and what has been learned about the underlying failure mechanisms and their effect on product lifetime and service. It recounts some of the tragic events that led to the discovery of fatigue and brittle fracture and explains how they reshaped design philosophies, procedures, and tools. It also discusses the influence of material and manufacturing defects, operating conditions, stress concentration and intensity, temperature and pressure, and cyclic loading, all of which play a role in the onset of fatigue cracking and thus should be considered when predicting useful product life.

This chapter briefly outlines some of the basic aspects of failure analysis, describing some of the basic steps and major concerns in conducting a failure analysis. A brief review of failure types from fracture, distortion, wear-assisted failure, and environmentally assisted failure (corrosion) is also provided.

Boiler tubes subjected to cyclic or fluctuating loads over extended periods of time are prone to fatigue failure. Fatigue can occur at relatively low stresses and is implicated in almost 80% of the tube failures in firetube boilers. This chapter covers the most common forms of boiler tube fatigue, including mechanical or vibrational fatigue, corrosion fatigue, thermal fatigue, and creep-fatigue interaction. It discusses the causes, characteristics, and impacts of each type and provides several case studies.

After several failed attempts to lower their starboard wheels for landing, pilots engaged the help of gravity through g-force maneuvers and managed to coax the wheels into place. An inspection following the incident revealed a broken universal joint in one of the linkages that opens and closes the doors to the undercarriage compartment. The failed component was removed from the aircraft and examined using optical and electron microscopes. Under low magnification, the fracture surface appeared jagged except for one corner that was relatively smooth. SEM fractography revealed the presence of fatigue striations in the smooth region and dimpling elsewhere. Based on their findings, investigators concluded that fatigue loading initiated a crack in the universal joint that progressed with time and that the final fracture occurred due to bending tensile overload.

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 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 gives a brief overview of the role of fatigue in component failures. It presents examples of fatigue failures along with statistics on the causes and costs of fatigue damage in various industries. It also includes a chapter-by-chapter summary of the content in the book, noting that the book deals primarily with fatigue at temperatures below the creep range with high-temperature fatigue being treated in a companion publication.

Durability is a generic term used to describe the performance of a material or a component made from that material in a given application. In order to be durable, a material must resist failure by wear, corrosion, fracture, fatigue, deformation, and exposure to a range of service temperatures. This chapter covers several types of component and material failure associated with wear, temperature effects, and crack growth. It examines temperature-induced, brittle, ductile, and fatigue failures as well as failures due to abrasive, erosive, adhesive, and fretting wear and cavitation fatigue. It also discusses preventative measures.

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.

This appendix focuses on procedures, techniques, and precautions associated with the investigation and analysis of metallurgical failures that occur in service. It describes the steps of an orderly failure analysis from collecting and examining samples to performing mechanical and nondestructive tests, preparing and examining fractographs and micrographs, determining failure mode, writing the report, and developing follow-up recommendations. It also examines the fundamental mechanisms of failure, why they occur, and how to identify them by their characteristic features.

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.

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.

The wear caused by contact stress fatigue is the result of a wide variety of mechanical forces and environments. This chapter discusses the characteristics of four types of contact stress fatigue on mating metal surfaces: surface, subsurface, subcase, and cavitation. Features and corrective actions for these contact stress fatigue are discussed. The chapter also lists some possible ways to reduce the cavitation fatigue problem.