Composite Material Defects Characterization Using Leaky Lamb Wave Dispersion Data

Leaky Lamb waves (LLW) propagation in composite materials has been studied extensively since it was first observed in 1982. The wave is induced using a pitch-catch arrangement and the plate wave modes are detected by identifying minima in the reflected spectra to obtain the dispersion data. The wave behavior in multi-orientation laminates was well documented and corroborated experimentally with a very high accuracy. The sensitivity of the wave to the elastic constants of the material and to its boundary condition led to several studies where the elastic properties were inverted and the characteristics of bonded joint were evaluated. Recently, the authors modified their experimental setup to allow measuring dispersion curves at a significantly higher speed than ever recorded. A set of 20 angles of incidence along a single polar angle of a composite laminate are acquired in about 45 seconds. The reflection spectra are acquired in real time while filtering the high frequency noise providing reliable data at amplitude levels that are significantly lower that were acquired in prior studies. This new method makes the LLW a practical 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 and the effect of flaws is analyzed and compared to the experimental data using a C-scan mounted LLW scanner.