Experimental assessment of guided waves far-field scattering around damage in metallic and composite structures

Abstract

Experimental damage simulation is useful for designing ultrasonic guided-wave based systems for non-destructive evaluation (NDE) and structural health monitoring (SHM). However, simulating the scattering of guided waves with geometrical (rivets, thickness changes, stiffeners, and extrusions) or damage features (fatigue cracks, fillet cracks, delaminations, and disbonds) remains a challenge. The objective of this work is to assess to which extent the interaction of ultrasonic guided waves with typical damage can be captured with an experimental model for a metallic structure and a composite structure. For the metallic structure, real fatigue cracks around a rivet hole are simulated by machined notches, while, for the composite structure, the impact damage is simulated by a single artificial delamination introduced into the laminate using two circular Teflon tapes during manufacturing. This paper implements an experimental methodology for estimating the far-field scattering for both simulated and real damage. Two co-localized rectangular piezoceramics are used to generate the guided waves and non-contact measurement is performed using a three-dimensional laser Doppler vibrometer (3D-LDV) to extract the required information for evaluation of the reflection, transmission, as well as the scattering behavior of the waves. The corresponding coefficients as a function of frequency, incident angle, and type of damage are extracted.