Fuel weep holes in aircraft wing risers are common fatigue critical locations forcrack initiation. Whilst cracks that grow from the surface of the weep holes toward thewing skin can be easily inspected outside the aircraft by traditional ultrasonic andcurrent state-of-the-art stress wave based SHM methodologies, cracks that grow awayfrom the wing-skin on the blind side of the hole pose a much greater challenge,particularly if the hole is an elongated slot. The damage from elongated slots, or fuelflow vent holes, can be located entirely within the shadow region with respect to thestraight non-diffracting rays from surface-mounted actuators. This paper investigatesthe diffraction and subsequent scattering of the fundamental symmetric Lamb, shearhorizontal and edge-guided Rayleigh-type wave modes from representative subsurfaceand hard-to-inspect damage on slotted fuel flow vent holes. It is shown with3D laser vibrometry and 3D finite element simulations that the edge-guided Rayleightypewave propagating along the free surface of the slot can play a key role in thedetection and health monitoring of damage located entirely within the shadow zone.
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