This chapter discusses field, visual, physical, and metallurgical examinations of gear failures. Physical examinations reviewed include nondestructive testing, including magnetic-particle inspection, tooth characteristic studies, surface hardness testing, ultrasonic testing, nital etching, profilometer measurements, and dimensional checking. Metallurgical examinations reviewed include the cross-sectional hardness survey, macroscopic examination, carbon gradient traverse, chemical analysis, case hardness traverse [microhardness], microscopic examination, and scanning electron microscopy.

This chapter describes several macroscopic examination techniques, including macroetching, contact printing, fracturing, and lead exudation. It explains how each method is implemented, why it is used, and what it reveals about manufacturing processes, defects, imperfections, and failure mechanisms.

This chapter provides an overview of the tools and techniques used to examine failure specimens and the wealth of information that can be obtained from fracture surfaces, cracks, wear patterns, and other such features. It discusses the use of metallography, fractography, and optical and electron microscopy. It presents a number of images recorded using these methods and explains what they reveal about the mode of fracture and the state of the component prior to failure.

This chapter describes nondestructive evaluation (NDE) test methods and their relative effectiveness for diagnosing the cause of stress-corrosion cracking (SCC) service failures. It discusses procedures for analyzing various types of damage in carbon and low-alloy steels, high-strength low-alloy steels, hardenable stainless steels, austenitic stainless steels, copper-base alloys, titanium and titanium alloys, aluminum and aluminum alloys, and nickel and nickel alloys. It identifies material-environment combinations where SCC is known to occur, provides guidelines on how to characterize cracking and fracture damage, and explains what to look for during macroscopic and microscopic examinations as well as chemical and metallographic analyses. It also includes nearly a dozen case studies investigating SCC failures in various materials.

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 chapters discusses the basic steps in the failure analysis process. It covers examination procedures, selection and preservation of fracture surfaces, macro and microfractography, metallographic analysis, mechanical testing, chemical analysis, and simulated service testing.

This article introduces the subject of fractography and how it is used in failure analysis. The discussion covers the structure of and fracture and crack-propagation behavior of polymeric materials, the distinction between the ductile and brittle fracture modes on the basis of macroscopic appearance, and the examination and interpretation of the features of fracture surfaces. In addition, the article considers several cases of field failure in various polymers to illustrate the applicability of available analytical tools in conjunction with an understanding of failure mechanisms.

This chapter examines the surface interactions that occur during metal forming operations at both the macroscopic and microscopic scale. It describes the measurement and characterization of surface profiles based on form error, waviness, and roughness. It explains how workpiece surfaces become rougher or smoother due to the effects of deformation, tooling interactions, and lubricant film thickness. It familiarizes readers with the concept of nominal contact, the role of asperities, and the effects of interface pressure, plasticity index, shear stress, and bulk strain rate. It also reviews the two basic friction rules applicable to metal forming and presents advanced friction models that account for the transition between Coulomb and Tresca behavior and the effects of lubrication.

This chapter explains how to take the known facts of a specific failure, place them in a systematic context to arrive at a logical conclusion, and point to a corrective measure. It presents example examinations to describe a systematic approach to failure examination.

A cardon shaft operating in an aircraft engine failed and was taken out and analyzed to determine the cause. A photograph of the broken shaft in the as-received condition shows the location and orientation of the fracture. The fracture surface appeared smooth, indicating that a considerable amount of rubbing occurred after the shaft broke. SEM fractography revealed deformation marks and elongated dimples, typical of shear overloads, along with other details. Based on their analysis, investigators concluded that the cardan shaft failed under torsional overload. They also cited a need for a more detailed examination of the driven end of the shaft.

A second-stage compressor blade in an aircraft engine fractured after 21 h of service. The remaining portion of the blade was removed and examined as were several adjacent blades. Based on the results of SEM fractography, microstructural analysis, and hardness testing, the blade failed due to stress-corrosion cracking combined with the effects of inadequate tempering.

This chapter describes an investigation following an aircraft accident in which the main undercarriage struts had failed. Visual examination revealed that the starboard strut fractured about 13 cm from the end nearest the underside of the wing. A close-up view of the fracture surface indicated that cracking initiated at the outer periphery of the strut and propagated inward until overload fracture occurred. SEM imaging revealed fatigue striations along the outer periphery and dimples elsewhere, indicative of tensile overload. Based on these observations, investigators concluded that the starboard strut failed by fatigue, which overloaded the port side strut as evidenced by its slant type fracture pattern.

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.

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.

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.

This chapter provides an overview of the possible mechanisms of failure for heat treated steel components and discusses the techniques for examining fractures, ductile and brittle failures, intergranular failure mechanisms, and fatigue. It begins with a description of the general sources of component failure. This is followed by a section on the stages of a failure analysis, which can proceed one after the other or occur at the same time. These stages of analysis are collection of background data, preliminary visual examination, nondestructive testing, selection and preservation of specimens, mechanical testing, macroexamination, microexamination, metallographic examination, determination of the fracture mechanism, chemical analysis, exemplar testing, and analysis and writing the report. The chapter ends with a discussion on various processes involved in the determination of the fracture mechanism.

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.

Fatigue fractures are generally considered the most serious type of fracture in machinery parts simply because fatigue fractures can and do occur in normal service, without excessive overloads, and under normal operating conditions. This chapter first discusses the three stages (initiation, propagation, and final rupture) of fatigue fracture followed by a discussion of its microscopic and macroscopic characteristics. The relationship between stress and strength in fatigue is explained. The next section provides information that may help the uninitiated to appreciate some of the problems of laboratory fatigue testing and of the fatigue process itself. Finally, information on types and statistical aspects of fatigue is provided along with examples.

This article reviews nondestructive and destructive test methods used to characterize welds. The first process of characterization discussed involves information that may be obtained by direct visual inspection and measurement of the weld. An overview of nondestructive evaluation is included that encompasses techniques used to characterize the locations and structure of internal and surface defects, including radiography, ultrasonic testing, and liquid penetrant inspection. The next group of characterization procedures discussed is destructive tests, requiring the removal of specimens from the weld. The third component of weld characterization is the measurement of mechanical and corrosion properties. Following the discussion on the characterization procedures, the second part of this article provides examples of how two particular welds were characterized according to these procedures.