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

This chapter explains how investigators determined that a stabilizer link rod fractured due to overload, possibly by a combination of tension and bending forces that occurred during an accident. It includes images comparing the fractured rod with its undamaged counterpart recovered from the starboard side of the aircraft. A close-up view of the threads near the fracture surface provides evidence of bending, while the presence of dimples in an SEM fractograph supports the theory that the link rod failed as a result of overload.

Fastening screws used in fuel-injection pumps failed during assembly and were examined to determine the cause. Based on observations and the result SEM fractography and hardness measurements, the screws failed by brittle intergranular fracture due to hydrogen embrittlement associated with plating procedures. The report includes recommendations for improving the quality of the screws.

This chapter discusses the failure of an aileron control cable in an aircraft and explains how investigators determined the cause. Based on their observations and the results of SEM fractography, investigators concluded that the cable had been damaged by a shearing tool, leading to its failure.

Structural members in a radar antenna system are held together by cadmium-plated high-strength steel bolts, several of which had fractured along the fillet near the head. Investigators determined that the bolts did not seat properly, making contact only at the periphery, which subjected them to high stress concentrations in the fillet region. They also concluded that the intergranular nature of the fracture, as revealed by scanning electron fractography, pointed to hydrogen embrittlement as a contributing factor. This chapter provides a summary of the investigation along with a recommendation to consider adding spring washers to the assembly.

This chapter discusses the failure of a control cable on an aircraft and the findings of an investigation that followed. The cable was made of stranded steel wire that was visibly worn. All seven strands had snapped and bore evidence of corrosion, pitting, nicks, and rubbing. Based on their observations and the results of SEM fractography, investigators concluded that tensile overload was the predominate cause of failure.

A high-pressure turbine blade in an aircraft engine failed prematurely, fracturing close to the root. Visual examination revealed significant plastic deformation on the leading edge of the blade, blocky cleavage on the trailing edge, and a region covered with fissures in between. Based on their observations and the results of SEM imaging described in the chapter, investigators concluded that the blade failed by low-cycle fatigue, acting on a preexisting crack.

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.

An aircraft tire burst while inflating, causing one of the flanges on the wheel hub to fracture. This chapter provides a summary of the investigation along with key findings. It includes images of the damaged hub and describes how various parts failed as the pressure in the tire increased. It explains that the hub material was of good quality under uniform load and that it fractured quickly by cleavage due to the force exerted by the overinflated tire.

An aircraft went down over water some 30 minutes into a flight. The wreckage was retrieved and the elevator linkage components were dismantled, cleaned, and reassembled. As the chapter explains, both the port and starboard hinge pins had fractured at a tack welded joint along a flange. Based on visual examination, SEM fractography, and chemical analysis, investigators concluded that the hinge pins were not made from the specified steel and were not properly treated after cadmium plating. The pins failed due to hydrogen embrittlement, which may have been aggravated by welding. The chapter provides several recommendations to avoid such failures in the future.

During a major servicing of an aircraft, cracks were found in the bottom wing root fitting. Based on dye penetrant inspection and the results of SEM fractography and chemical analysis, investigators concluded that the cracks were due to stress corrosion. They also recommended an inspection of all other aircraft with similar fittings and the consideration of alternate materials that are less prone to stress-corrosion cracking.

This chapter discusses the failure of a compressor blade in an aircraft engine and explains how investigators determined the cause. Based on visual examination and the results of SEM fractography and chemical analysis, it was concluded that blade failed due to fatigue fracture originating from nonmetallic inclusions in the blade root.

The nose landing gear on an aircraft malfunctioned during landing roll. After the incident, two fractured studs were found in the retraction jack support beam. Based on visual examination and the results of SEM fractography, investigators concluded that the studs failed by fatigue, a vulnerability because of the way they were mounted. A sketch showing the correct mounting configuration is included in the report.

This appendix is a compilation of suggested analysis methods for suspected component failure causes.

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 discusses some of the more advanced methods and procedures used in failure analysis, including in-service material sampling, in situ microstructure analysis, and a form of punch testing that can determine the fracture toughness of any material from a tiny specimen. The chapter also covers quantitative fractography, fracture surface topography analysis, and the use of oxide dating as well as fault tree and failure modes and effects analysis (FMEA) and computational techniques.

An aircraft was heavily damaged when it was forced to land due to a throttle malfunction. Investigators determined that one of the studs linking the throttle to the engine fractured from fatigue, initiated by cracks formed during a riveting procedure. This chapter provides a summary of the investigation, which included the use of scanning electron fractography, along with recommendations on acceptable hole patterns for rivets.