An experimental and computational study of Lamb wave scattering by edge delaminations around circular holes

This paper presents a study on the scattering of the fundamental flexural Lamb wave mode (A0) by an edge delamination around the circumference of a circular through hole in a plate. Although edge delaminations are recognized as an important form of structural damage in fiber-composite laminates, there is little previous work on Lamb wave scattering by this form of damage This study uses a 3D laser vibrometer to obtain a detailed experimental characterization of the angular dependence of the scattered field from an edge delamination, for an incident probing wave at various angles of incidence. These experimental observations are correlated with computational results obtained by using the commercial Finite Element package ABAQUS, showing excellent correlation. To assist with a detailed quantitative analysis of this complicated scattering process, Aluminium is used instead of a composite laminate, as this removes further complications that arise due to the anisotropic and multilayer nature of the material in composites. A simulated semi-circular delamination is introduced at the boundary of a circular hole of 20mm diameter, in the mid plane location of the plate using cutting tool. The probing signal is a narrowband 5.5-cycle tone burst with a center frequency of 200 kHz, for which the corresponding A0 wavelength is λ = 10 mm. The relatively small damage size studied corresponds to early damage detection which is the main area of interest for SHM applications The Scattered Amplitude Pattern is used to study the relationship between the scattered field and damage orientation relative to the incident wave. Results obtained indicate a strong dependence between the scattering amplitude pattern and angle of incidence. The results show that the scatter field amplitude and directivity information can be used to detect and quantify the damage in any orientation around the through hole, which confirms and extends the correlations obtained in our previous work for delaminations at a straight edge. This forward scattering problem provides a necessary pre-requisite for addressing the more challenging inverse problem of characterizing the damage from observations of the scattered field, particularly for complex geometries involving detection on the blind side of through holes.