2. Mechanism: analysis based on visual examination

Visual inspection is a non-destructive testing method which is often simple to implement, but which is also highly instructive, as it helps to explain the inspection mechanism.

This involves observing the surface of an object to detect any anomalies. This observation requires a light source of intensity and wavelength compatible with the natural eye ability of the operator performing the examination.

The process involved (figure 1 ) can be broken down into three essential phases:

• excitation, which consists in producing a beam of white or monochromatic light;

• perturbation, which...