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.

Microstructural analysis of the composite matrix is necessary to understand the performance of the part and its long-term durability. This chapter focuses on the microstructural analysis of engineering thermoplastic-matrix composites and the influence of cooling rate and nucleation on the formation of spherulites in high-temperature thermoplastic-matrix carbon-fiber-reinforced composites. It also describes the microstructural analysis of a bio-based thermosetting-matrix natural fiber composite system.

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.

A low-pressure turbine rotor blade failed in service, causing extensive engine damage. A section of the blade broke off around 25 mm from the root platform, producing a flat fracture surface that appeared smooth on one end and grainy elsewhere. Based on their examination, investigators concluded that the nickel-base superalloy blade was exposed to high temperatures and stresses, initiating a crack that propagated under cyclic loading. This chapter provides a summary of the investigation and the insights acquired using scanning electron fractography, metallography, and hardness measurements.

A turbine blade in an aircraft engine failed, fracturing at the root above the fir tree region. Fractography indicated that a fatigue crack initiated at the trailing edge of the blade and the final fracture occurred when the crack reached critical length. Although the exact cause of crack initiation could not be established, material defects, improper root loading, and high operating temperatures were ruled out. This chapter describes how investigators came to their conclusions and what they learned through visual and SEM examination and qualitative elemental analysis. It includes images of the microstructure and fracture surfaces and explains what some of the details reveal about the failure.

A pair of bearings mounted side by side in an aircraft engine failed in service. Photographs show that the inner rings were either broken or deformed, the balls were worn and flattened, and the cages severely damaged. The bearing races were damaged as well, but only on one side indicating a directional thrust. In addition to their examination, investigators also conducted metallographic studies and hardness tests, which indicated that the balls and inner rings reached temperatures above 825 °C (1520 °F). Based on their findings, investigators concluded that the bearings failed due to overheating, possibly as a result of misalignment compounded by insufficient lubrication and high speeds.

A test flight was cut short after a fire warning came on indicating a problem with one of the four engines on an aircraft. A visual examination following the precautionary landing revealed several burned hoses, a melted bolt, and fuel leaking from the base of the main burner. The fuel nozzle was also damaged, and based on its microstructure, came very close to melting. Investigators determined that the burner was mounted backwards, facing the compressor rather than the turbine. They also recommended a redesign to prevent the fuel nozzle from being reversed.

An aircraft crashed following the loss of yaw control in full airborne flight. The subsequent discovery of broken shutter bolts in the rear pitch reaction control valve led to an inspection campaign that found bolt failures of a similar nature in valves on several other aircraft. The bolts were removed and analyzed to determine the mode and cause of failure. Based on the results of macroscopy, scanning electron fractography, metallographic examination, and chemical analysis, the failures were caused by stress corrosion cracking, and in one case, overtightening.

A compressor blade made of titanium alloy fractured during an engine test. The material and processing conditions of the blade were found to be satisfactory, turning the focus of the investigation to operating anomalies and human error. A photograph of the failed blade shows well-defined chevron marks along the fracture surface that end in a shear lip on the convex side. Further examination using a SEM shows that the failure was due to overload. Based on these observations and the results of tensile testing and microstructural analysis, investigators concluded that a sudden impact load on the concave side of the blade caused it to fracture.

This report describes the failure of a gas turbine in a combined-cycle power plant and the examination and tests that were conducted to determine the cause. Based on microstructural analysis, hardness measurements, and tensile tests, the failure was attributed to inadequate clearances in the seal land region between two stages in the compressor section of the rotor. The report also recommends changes to remediate the problem.

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 discusses the techniques applicable to the diagnosis of corrosion failures, including visual and microscopic examination of corroded surfaces and microstructure; chemical analysis of the metal, corrosion products, and bulk environment; nondestructive evaluation methods; corrosion testing techniques; and mechanical testing techniques. A guide to investigative techniques used in corrosion failure analysis is provided in a table, describing the advantages and limitations of each technique. The principal stages of the investigation and analysis of corrosion failures discussed in the chapter are: collection of background information and sampling; preliminary laboratory examination; detailed metallographic and fractographic examinations; chemical analysis of corrosion products and bulk materials; corrosion testing for quality control; mechanical testing for quality control; and analysis of results and report writing.

This chapter covers the emerging practice of quantitative microscopy and its application in the study of the microstructure of metals. It describes the methods used to quantify structural gradients, volume fraction, grain size and distribution, and other features of interest. It provides examples showing how the various features appear, how they are measured, and how the resulting data are converted into usable form. The chapter also discusses the quantification of fracture morphology and its correlation with material properties and behaviors.