4. Classification of Techniques and Technologies

The wide variety of materials used in industrial equipment has led research organizations and companies specializing in preventive maintenance to deepen their understanding of the physical mechanisms of degradation in order to develop increasingly effective diagnostic techniques. Today, there are dozens of technologies, many of which are specifically designed to detect a particular phenomenon.

There are generally two main categories of techniques.

• First category: physical signatures of material changes. These methods utilize information generated by external excitations, with signals covering an extremely broad spectrum, ranging from a few fractions of a hertz (infrasound) to 10 ²⁵ hertz (X-rays). These techniques fall under the category of non-destructive testing (NDT) or non-destructive...