Vibrothermography is an active IR thermography technique where, under the effect of mechanical vibrations induced externally to the structure at a few fixed frequencies (based on the availability of commercial equipment), heat is released by friction precisely at defect locations (such as cracks and delaminations). In such experiments, direct conversion from mechanical to thermal energy occurs and flaws are excited at specific mechanical resonances: local subplates formed from delamination presence resonate independently of the rest of the structure at particular frequencies).Consequently, by changing (increasing or decreasing) the mechanical excitation frequency, local thermal gradients may appear or disappear. However, in current practice, fixed frequency excitation is commonly used, largely as a matter of convenience and commercial availability.

Vibrothermography most significant advantages are:

• detection of flaws hardly visible by other IR thermography schemes (such as for instance closed cracks in gears);
• inspection of large structural areas in situ.

On the other hand, the required mechanical loading may be difficult to achieve.