Inspection of aircraft structural components using lock-in thermography

Lockin thermography with its capability to monitor modulated heat flow in larger areas (several m 2 ) within a few minutes is applied to the inspection of aircraft. Using up to 6 lamps each with a power of 1 kW, we could inspect subsurface structures (e.g. stringers) and subsurface defects (e.g. impact, delaminations) from a distance of several meters. The method is well suited to monitor the structural integrity of aging aircraft in the near-surface area. By using ultrasonic excitation instead of radiation one can display selectively hidden defects that are characterised by a local enhancement of mechanical loss angle (e.g. cracks).