Guided Waves in a Disbonded Honeycomb Composite Structure

Damage identification using ultrasonic nondestructive evaluation (NDE) requires a good understanding of the properties of the various types of waves that can be transmitted in the structure in presence or absence of damage. For successful application of these techniques to locate and estimate the severity of the damage, it is extremely important to understand the propagation characteristics of ultrasonic waves in these structures. Wave propagation in composites is extremely complex due to material inhomogeneity and anisotropy, where characteristics of the waves depend on the laminate layup, direction of wave propagation, frequency, and interface conditions. When elastic waves are generated by surface sources in a plate, they experience repeated reflections at the top and bottom surfaces alternately. The mutual interference of the reflected waves results in propagation guided by the plate surfaces. In this paper a specific structure will be analyzed with different levels of complexities as far as the wave propagation characteristics are concerned. The structure is a sandwich plate composed of two carbon-epoxy face sheets with an aluminum honeycomb core with hexagonal cells. The work is carried out using theoretical analysis, numerical models and experimental verifications. Numerical (Finite Element) models are used for more practical cases, for which the geometric and material complexities of actual structures present practical difficulties in direct analysis of wave propagation data using theoretical constructs only.