Glasses and ceramics are susceptible to stress-corrosion cracking (SCC), as are metals, but the underlying mechanisms differ in many ways. One of the major differences stems from the lack of active dislocation motion that, in metals, serves to arrest cracks by reducing stress concentrations at flaw tips. As a result, even relatively small flaws (20 to 50 μm in radius) can cause glasses and ceramics to fail. This chapter examines the propensity of flaws to grow in glass and ceramic materials exposed to different environments, especially water, at stresses well below those that would produce immediate failure. It describes crack growth mechanisms, explains how to measure crack growth rates and predict time to failure, and provides crack growth data for a number of materials and environments.

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 describes tensile testing of advanced ceramic materials, a category that includes both noncomposite, or monolithic, ceramics and ceramic-matrix composites (CMCs). The chapter presents four key considerations that must be considered when carrying out tensile tests on advanced monolithic ceramics and CMCs. These include effects of flaw type and location on tensile tests, separation of flaw populations, design strength and scale effects, and lifetime predictions and environmental effects. The chapter discusses the advantages, problems, and complications of four basic categories of tensile testing techniques as applied to ceramics and CMCs. These categories are true direct uniaxial tensile tests at ambient temperatures, indirect tensile tests, tests where failure is presumed to result from tensile stresses, and high-temperature tensile tests.

This chapter explains how to recognize decarburization and related defects. It includes images showing how decarburization appears in various steels, discusses stock removal practices, and describes common defects and flaws such as quench cracks and where they are typically found.

Ultrasonic inspection is a nondestructive method in which beams of high frequency acoustic energy are introduced into a material to detect surface and subsurface flaws, to measure the thickness of the material, and to measure the distance to a flaw. This chapter begins with an overview of ultrasonic flaw detectors, ultrasonic transducers, and search units and couplants. It then discusses the principles of operation, presentation, and interpretation of data of pulse echo and transmission methods. This is followed by sections providing information on general characteristics of ultrasonic waves and the factors influencing ultrasonic inspection. The advantages, disadvantages, and applications of ultrasonic inspection are finally compared with other methods of nondestructive inspection of metal parts.

This chapter discusses the failure of a first-stage compressor blade in an aircraft engine and explains how investigators determined that it was caused by fatigue, with a crack originating from corrosion pits that developed in the root transition region on the convex side of the airfoil.

This chapter presents a fracture-mechanics-based approach to damage tolerance, accounting for mechanical, metallurgical, and environmental factors that drive crack development and growth. It begins with a review of stress-intensity factors corresponding to a wide range of crack geometries, specimen configurations, and loading conditions. The discussion covers two- and three-dimensional cracks as well as the use of correction factors and problem-simplification techniques for dealing with nonstandard configurations. The chapter goes on to describe how fatigue loading affects crack growth rates in each of the three stages of progression. Using images, diagrams, and data plots, it reveals how cracks advance in step with successive stress cycles and explains how fatigue crack growth rates can be determined by examining striations on fracture specimens and correlating their widths with stress profiles. It also describes how material-related factors, load history, corrosion, and temperature affect crack growth rates, and discusses the steps involved in life assessment.

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.

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.

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.

Fracture is the separation of a solid body into two or more pieces under the action of stress. Fracture can be classified into two broad categories: ductile fracture and brittle fracture. Beginning with a comparison of these two categories, this chapter discusses the nature and causes of these failure modes. Some body-centered cubic and hexagonal close-packed metals, and steels in particular, exhibit a ductile-to-brittle transition when loaded under impact and the chapter describes the use of notched bar impact testing to determine the temperature at which a normally ductile failure transitions to a brittle failure. The discussion then covers the Griffith theory of brittle fracture and the formulation of fracture mechanics. Procedures for determination of the plane-strain fracture toughness are subsequently covered. Finally, the chapter describes the effects of microstructural variables on fracture toughness of steels, aluminum alloys, and titanium alloys.

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 provides an overview of the various inspection methods used with metals and alloys, namely visual inspection, coordinate measuring machines, machine vision, hardness testing, tensile testing, chemical analysis, metallography, and nondestructive testing. The nondestructive testing methods discussed are liquid penetrant inspection, magnetic particle inspection, eddy current inspection, radiographic inspection, and ultrasonic testing.

In forgings of both ferrous and nonferrous metals, the flaws that most often occur are caused by conditions that exist in the ingot, by subsequent hot working of the ingot or the billet, and by hot or cold working during forging. The inspection methods most commonly used to detect these flaws include visual, magnetic particle, liquid penetrant, ultrasonic, eddy current, and radiographic inspection. This chapter provides a detailed discussion on the characteristics, process steps, applications, advantages, and limitations of these methods. It also describes the flaws caused by the forging operation and the principal factors that influence the selection of a nondestructive inspection method for forgings.

This chapter focuses on the inspection of steel bars for the detection and evaluation of flaws. The principles involved also apply, for the most part, to the inspection of steel wire. The nondestructive inspection methods discussed include magnetic particle inspection, liquid penetrant inspection, ultrasonic inspection, and electromagnetic inspection. Eddy current and magnetic permeability are also covered.

This chapter discusses the basic steps of a failure investigation. It explains that the first step is to gather and document information about the failed component and its operating history. It advises investigators to visit the failure site as soon as possible to record damages and collect test specimens for subsequent examination and chemical analysis. It also discusses the role of mechanical property testing, the use of nondestructive evaluation, and the final step of generating a report.

Wrought tubular products are nondestructively inspected chiefly by eddy current techniques (including the magnetic flux leakage technique) and by ultrasonic techniques. The methods discussed in this chapter include eddy current inspection, flux leakage inspection, ultrasonic inspection, magnetic particle inspection, liquid penetrant inspection, and radiographic inspection of resistance welded tubular products, seamless steel tubular products, and nonferrous tubular products. This chapter discusses the fundamental factors that should be considered in selecting a nondestructive inspection method and in selecting from among the commercially available inspection equipment. The factors covered are product characteristics, nature of the flaws, extraneous variables, rate of inspection, end effect, mill versus laboratory inspection, specification requirements, equipment costs, and operating costs.

This chapter explains how metallography and hardness testing are used to evaluate the quality and condition of metal products. It also discusses the use of tensile testing, fracture toughness and impact testing, fatigue testing, and nondestructive test methods including ultrasonic, x-ray, and eddy current testing.