24. Damage Detection and Visco-Elastic Property Characterization of Composite Aerospace Panels Using Ultrasonic Guided Waves

Composite materials are widely used in commercial and military aircraft. A major concern is the detection and quantification of damage in these panels caused, for example, by foreign object impacts. A related issue is the characterization of the composite visco-elastic properties, whether the ply-by-ply properties or the laminate’s engineering properties. Both of the aforementioned tasks can be accomplished by careful use of ultrasonic guided waves that are multimode and dispersive waves propagating in the composite waveguide. The test piece for these studies is a carbon-reinforced plastic (CFRP) panel with co-cured stiffeners representative of modern commercial aircraft construction (e.g. B787). The wave dispersive properties of this panel were first determined from broadband ultrasonic tests and 2D Fourier Transform techniques. A Semi-Analytical Finite Element (SAFE) analysis was then performed to calculate dispersion curves and cross-sectional mode shapes of relevant guided modes propagating in the panel. The SAFE analysis allowed to iteratively change the elastic properties of each layer in the panel so as to identify the layer-by-layer properties from the experimental extraction of the dispersive guided waves propagating in the test panel. A scanning inspection system using air-coupled ultrasonic transducers operating at specific frequencies was also developed to detect and quantify impact-induced damage in the skin or the stringer of the panel.