Guided Wave Techniques for Damage Detection in Composite Aerospace Structures

Composite materials make up an increasing portion of today’s aerospace structures (see, e.g. Boeing 787 and Airbus 380). These aircrafts’ fuselage, for example, is composed of a laminated composite skin connected to composite stringers and C-frames. Of primary importance is the detection of damage in these built-up structures, whether caused by the manufacturing process or in service (e.g. impacts). A related issue is the characterization of the composite (visco)elastic mechanical properties, that can also be related to the quantification of potential damage. Guided elastic waves propagating in the ~100s kHz regime lend themselves to provide the necessary sensitivity to these two conditions (damage and mechanical properties). This presentation will discuss the use of these waves to provide information on both damage and mechanical properties of composite structures that are typically used in modern commercial aircraft fuselages. In particular, a scanning system using air-coupled ultrasonic transducers and statistical processing will be presented for the detection and the quantification of impact-induced damage in laboratory test panels representative of fuselage construction. A Semi-Analytical Finite Element (SAFE) technique will be presented to identify the layer-by-layer properties of the composite skin laminate by observation of the guided wave dispersive behaviour. Finally, a technique to use SAFE analysis in structures of non-uniform cross-section (able, for example, to model the guided wave propagation from the composite skin into the skin-to-stringer assembly) will be proposed by utilizing concepts of Global-Local modelling that use normal-mode expansion and boundary continuity.