Weep Hole Inspection for Radial Fatigue Cracks by Circumferential Creeping Waves

Abstract

Weep holes are drilled through risers in wet-wing structures in order to permit remanent fuel to be evenly distributed during flight. Unfortunately, they can become the sites from which fatigue cracks tend to originate. Figure 1 shows the schematic diagram of weep holes cut into the vertical risers of an airplane wing used as a fuel tank. The cracks have been found to grow in either the upward or downward or both directions. These fatigue cracks initially grow in a radial direction perpendicular to the wing skin surface. Downward growing cracks can be easily detected using a 45-degree shear wave transducer. The main objective of this study was the development of an ultrasonic detection technique for the less accessible upward growing cracks. The blowup in Figure 1 shows the geometrical configuration of such an upward growing fatigue crack.