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Guided Wave Scattering for In Situ Health Monitoring of Slotted Fuel Flow Vents in Integral Stiffeners



Fuel weep holes in aircraft wing risers are common fatigue critical locations for crack initiation. Whilst cracks that grow from the surface of the weep holes toward the wing skin can be easily inspected outside the aircraft by traditional ultrasonic and current state-of-the-art stress wave based SHM methodologies, cracks that grow away from 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 fuel flow vent holes, can be located entirely within the shadow region with respect to the straight non-diffracting rays from surface-mounted actuators. This paper investigates the diffraction and subsequent scattering of the fundamental symmetric Lamb, shear horizontal and edge-guided Rayleigh-type wave modes from representative subsurface and hard-to-inspect damage on slotted fuel flow vent holes. It is shown with 3D laser vibrometry and 3D finite element simulations that the edge-guided Rayleightype wave propagating along the free surface of the slot can play a key role in the detection and health monitoring of damage located entirely within the shadow zone.

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