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NDE of bridging delamination using guided waves: Simulated and experimental results

Bridging delamination detection in rotor blade edges is difficult with NDE methods such as radiography and thermography. By bridging delamination we mean that the delaminated surfaces are in full or partial contact with each other along a curved geometry. An array of ultrasound sensors along a line can track guided Lamb wave propagation for NDE of composites, and are particularly useful for larger structures. Guided ultrasound waves, such as Lamb waves, when scattered from such defects, are shown to be detected along a line of Bragg grating fiber optic transducers. Simulation results from ANSYS models of curved composite samples with bridging defects that correlate well with our Lamb wave measurements have also been obtained. The models confirm what is observed in our experimental studies on laboratory specimens, that reflections of guided waves occur from delamination/bridging defects in the bends of rotor blades and aircraft leading edge type curved composite structures, and can be used to locate and identify these defects. Potential applications of these NDE techniques, and industrial components to which they are relevant, are discussed. A description of the sensor design and detection system is also outlined.