Eddy Current Techniques for Detecting Hidden Subsurface Defects in Multilayer Aircraft Structures

Abstract In-service non-destructive inspection (NDI) is a very important part of the aircraft maintenance program that minimizes breakdowns due to fracture critical components. The eddy current (EC) NDI method one most applicable methods for this purpose, its high sensitivity fatigue cracks and corrosion damage in main structural materials. In paper, selective double differential type EC probes characterized by enhanced possibility detecting subsurface initiated or stress phenomena are presented. For different applications, family was developed with sizes (from 5 33 mm) spatial resolutions. These types operational frequencies wide frequency range 0.2 kHz 1.0 MHz), penetration depth unique defects (like elongated local corrosive pitting), level specific noise suppression concerned scanning procedures. proposed were investigated as effective tools characteristic applications defect detection multilayer structures, such second layer riveted two-layer structure on side surface reinforcing hoop influence; arc welding rough surface; through repair patches fabricated from aluminum alloy carbon fiber reinforced plastic, etc. techniques create remarkable possibilities well-timed dangerous without disassembling removing protective coating.