Borescope and Eddy Current Dual Probe for In Situ Detecting Cracks in an Aeroengine Labyrinth Disc

Cracks often arise in an aeroengine labyrinth disc, which endanger flight security. Non-destructive testing (NDT) must been carried out in the labyrinth disc during the aeroengine working time. In situ detecting cracks in the labyrinth disc, the probe need pass through three layers narrow holes of aircraft skin, engine shell and outlet duct. Ultrasonic, radiography and liquid penetrant inspection cannot be employed. A probe containing several NDT devices will be a feasible means. Borescope is a most widely used method for detecting and examining surface cracks inside narrow tubes or difficult-to-reach chambers. But borescope cannot detect subsurface defects and cannot estimate the depth of cracks. Eddy current testing is sensitive to surface and subsurface defects of metal material. But when the interface between the eddy current probe and the object cannot come into view, it is hardly to operate correctly. These two techniques are complementary, and no detrimental interference is observed. A dual probe containing an eddy current probe and a borescope was designed for aeroengine labyrinth disc in this paper. An aeroengine labyrinth disc containing manufactured and real defects was detected using the dual probe. The results of testing show that borescope and eddy current dual probe can completely achieve in situ detecting cracks in an aeroengine labyrinth disc.