Characterization of Defects in Composite Materials using Rapidly Acquired Leaky Lamb Wave Dispersion Data

The phenomenon of Leaky Lamb waves (LLW) in composite materials was first observed in 1982 using a Schlieren system. It has been studied extensively by numerous investigators and successfully shown to be an effective quantitative NDE tool. In spite of the success, the method has not become a standard inspection technique due to shortcoming that will be addressed in this manuscript. The LLW phenomenon is associated with an ultrasonic pitch-catch setup and involves the measurements of the guided wave dispersion curves by identifying the minima in the reflected spectra. The sensitivity of the wave to the elastic constants of the material and the boundary conditions led to the development of methods of inverting the elastic properties and the characterization of bonded joint. Recently, the authors modified their experimental setup to rapidly measure dispersion curves allowing data acquisition speed that is faster than ever before. The reflection spectra are acquired in real time while filtering the high frequency noise providing reliable data at amplitude levels that are significantly lower than were acquired in prior studies. This new method makes the LLW more practical as a quantitative tool for both inversion of the elastic properties and characterization of flaws. The emphasis of the current study is on the detection and characterization of flaws. The composite is modeled as transversely isotropic and dissipative medium. Further, the effect of flaws is analyzed and compared to the experimental data using a C-scan mounted LLW scanner. 1