Propogation loss with frequency of ultrasound guided waves in a composite metal-honeycomb structure

Non-destructive testing of critical structural components is time consuming, while necessary for maintaining safe operation. Large aerospace structures, such as the vertical stabilizers of aircraft undergo inspection at regular intervals for damage diagnostics. However, conventional techniques for damage detection and identification before repair can be scheduled are conducted off-line and therefore can take weeks. The use of guided ultrasound waves is being investigated to expedite damage detection in composites. We measure the frequency dependent loss of ultrasonic guided waves for a structure comprising a boron-nitride composite skin sandwiching an aluminum honeycomb. A wide range of ultrasound frequencies propagate as measured using PZTs, with the lowest attenuation observed about 200-250 kHz. These measurements are confirmed using optical fiber Bragg grating arrays used as ultrasound transducers.