This chapter discusses the key findings of an investigation into the failure of an aircraft engine fuel pump. It explains how investigators came to the conclusion that metal slivers from a heavily worn spring may have interrupted the flow of lubricant to one of the slipper pads, causing adhesive wear and the welding of slipper pad material onto the surface of a mating cam plate. Excessive friction between the slipper pads and cam plate, in turn, created a torsional overload that caused the camshaft to break. The chapter presents SEM images showing the wear pattern on one of the springs along with photographs of the damaged slipper pads and cam plate. It also includes an image of a copper flake found in one of the pistons and discusses the results of qualitative x-ray chemical analysis.

Failure analysis is a systematic investigative procedure using the scientific method to identify the causes of a failure. This chapter begins by exploring what failure analysis is followed by a section describing the sequence of stages in the investigation and analysis of failure and the three principles that must be carefully followed during the analysis. It then provides information on the normal location of fracture and concludes with a list of questions to ask about fractures.

The mechanical behavior of a material, in the most practical sense, is how it deforms or breaks under load; in other words, how it responds when stressed. This chapter provides a brief review of the properties associated with mechanical behavior, including stress, strain, elasticity, plastic deformation, ductility, hardness, creep, fatigue, and fracture. It also describes the primary components of a Charpy impact tester and the role they serve.

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.

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.

Fracture control can be defined as a concerted effort to maintain operating safety without catastrophic failure by fracture. It requires an understanding of how cracks affect structural integrity and strength and the time that a crack can grow before it exceeds permissible size. The chapter describes some of methods used to determine maximum permissible crack size and predict growth rates. It explains how the information can then be used to control fractures through periodic inspection, fail-safe features, mandated retirement, and proof testing. It presents a number of fracture control plans optimized for different circumstances, examines the damage tolerance requirements used by different industries, and discusses various approaches for fatigue design.

This chapter focuses on common failure characteristics exhibited by mechanical and electrical components. The topic is considered from two perspectives: one possibility is that the system failed because parts were nonconforming to drawing requirements and another possibility is that the system failed even though all parts in the system met their drawing requirements. The common failures discussed in this chapter include those associated with metallic components, composite materials, plastic components, ceramic components, and electrical and electronic components.

This article depicts typical fractographic features for a number of different composite materials, covering interlaminar and translaminar fracture characteristics in composite materials.