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Fractography

Fractography is understood to mean "the study of fracture surfaces". In failure analysis, fractography is a vital tool used to determine a failure mode. The Scanning Electron Microscope (SEM) is often the choice instrument used to examine the surface of a failed material. When materials break in a brittle manner, they usually exhibit a crystalline or brittle appearing fracture.

Likewise, when a ductile material is fractured, the fracture surface usually exhibits elongated dimples. Often, exemplar fractures surfaces are prepared for comparison with the failed material.

An elemental x-ray analyzer (Energy Dispersive X-ray Analysis) is often used for elemental chemical analysis of anomalies on the fracture surface. EDXA produces a spectrum map of the elements present. This capability is a valuable tool for determining alloy segregation, elemental diffusion and dealloying of zinc in brass.

Terminology

The following terms relate to Fractography:

Diffusion
The process of intermingling atoms or other particles within a solution. In solids, it is a slow movement of atoms from areas of high concentration toward areas of low concentration The process may be (a) migration of interstitial atoms such as carbon, (b) movement of vacancies, or (c) direct exchange of atoms to neighboring sites.
Fracture Surface
A ruptured surface of a metal which contains the character or fracture mode causing the fracture. Fracture surfaces are often examined using the macroscope, optical microscope, and the scanning electron microscope to determine the actual cause of failure. Fatigue fractures, however, often display a smooth, clam-shell appearance.
Fracture Test
Nicking and breaking a bar by means of sudden impact, to enable macroscopic study of the fractured surface.
Macroscopic
Structural details observed with the naked eye and/or aided with low-power optics at magnifications up to 50x.
Macrostructure
The structure of metals as revealed by macroscopic examination.
  
  

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