Fractography

Fractography is the study of fracture surfaces of materials to determine the cause of failure. The method is used to study fracture surfaces in any material, such as metals, ceramics, glasses and polymers.

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The focus of fractographic examination is to determine the cause of failure by studying the characteristics of a fracture surface. Different modes of crack growth (e.g. fatigue, stress corrosion cracking, hydrogen embrittlement) produce characteristic features on the surface, which can be used to help identify the mode of failure.

Another important factor of fractography is to establish and examine the origin of cracking, as examination at the origin may reveal the cause of crack initiation. Common features that may be a cause for crack initiation are inclusions, voids or foreign materials, points of stress concentrations etc.

Methods

Initial fractographic examination is commonly carried out on a macro scale utilising low power optical microscopy and oblique lighting techniques to identify the extent of cracking, possible modes and likely origins. Some modes of crack growth can leave characteristic marks on the surface that identify the mode of crack growth and origin on a macro scale e.g beachmarks on fatigue cracks.

In most cases, fractography requires examination on a micro scale, which is most commonly carried out in a Scanning electron microscope.

Fractography is a widely used technique in forensic engineering and fracture mechanics to understand the causes of failures and also to verify the theoretical failure predictions with real life failures.

External links

• National Institute of Standards and Technology - Ceramics
• Southampton Fractography Online Resource
• Plymouth Fractography Resource
• Open University failed products museum