Fractography - Scanning Electron Microscopy

Scanning Electron Microscopy

In many cases, fractography requires examination at a finer scale, which is usually carried out in a Scanning electron microscope or SEM. The resolution is much higher than the optical microscope, although samples are examined in a partial vacuum and colour is absent. Improved SEM's now allow examination at near atmospheric pressures, so allowing examination of sensitive materials such as those of biological origin. The SEM is especially useful when combined with Energy dispersive X-ray spectroscopy or EDX, which can be performed in the microscope, so very small areas of the sample can be analysed for their elemental composition.

The fracture surface photograph shows a brittle fracture in a car brake seal. Crack growth can be seen from the fine lines or striations in the surface, indicative of fatigue. The problem led to an accident when the crack suddenly grew to completion, hydraulic fluid was lost, the driver lost braking power, and the vehicle crashed. The crack grew from cuts at the edge of the seal, probably caused by sharp particles trapped in the brake cylinder.