Application of Interface Waves for Damage Detection in Laminated Composite Bends

Abstract

This research investigates a novel ultrasonic method using guided interface waves for the inspection of curved hybrid laminate composite structures. Most composite airframe components, such as skin – stringer and web - flange attachment of beams and channels, form structural elements which are known as Noodles. Noodles or radius fillers are used to fill-out the radius bend of curved structures. Noodles are constructed from composites with orientations different from the primary laminated structure. Noodles are vulnerable to many forms of damages and flaws. Noodles are also located in areas that might not be very convenient for inspection by typical nondestructive methods. In this research, the propagation of ultrasonic guided interface waves in a skin – stringer configuration with noddle is studied. The surface acoustic wave on the curved outer surface is modeled. The intention is to identify effective guided waves for the structural curvature radius inspection. The guided wave propagation path along the bondline of skin – stringer and noodle area is simulated numerically by finite element model. Typical damage scenarios in the noodle area are modeled. The ultrasonic interface wave behavior is studied for several cases to characterize noodle damages. The attenuation and scattering of wave-front suggest the interface wave can detect several damages at certain frequency range, when the wavelength is compatible with the bend radius of the structure. Also the location of damage in the noodle area can be found by reflection sources from different defect sizes. This study can be used for a generalized solution of noodle inspection problem and in connection with examination of curved surface as part of the development of a structural health monitoring system.