An analytical study of the scattering of ultrasonic guided waves at a delamination-like discontinuity in a plate

Abstract

Interface delaminations between individual plies in a composite, or disbonds of face sheets in honeycomb structures often remain undetected. Using guided ultrasonic waves (Rayleigh and Lamb waves) such hidden defects can be detected. In this work, an analytical framework that considers propagating, nonpropagating and evanescent waves to analyze the scattering of an incident ultrasonic wave at a delamination-like discontinuity is presented. Wave conversion at the interface of the damage is quantified in terms of the power flows of the individual waves. The analytical solutions are compared with results from numerical simulations. For an incident Lamb wave, excellent agreement is found. However, it is shown that the analytical solution for an incident Rayleigh wave has significant differences from the numerical results, due to the incomplete nature of the Rayleigh wave-field in the half-space. Even though this study is performed for isotropic waveguides, the method can be extended to transversely isotropic laminates by substituting the corresponding expressions for the dispersion equations, as well as displacement and stress fields.

Core-Skin Disbond Detection in a Composite Sandwich Panel Using Guided Ultrasonic Waves

“…In this case, the segment above the crack acts as a newly formed waveguide for Lamb waves. In this region, "wave trapping" occurs under certain conditions, i.e., only low transmission to other waves occurs at the trailing edge of the crack [6,19]. Depending on the excitation frequency and thickness of the core of the sandwich panel, it is shown that the segment below the defect also acts as a waveguide for either Lamb or Rayleighlike waves.…”

“…Generally, scattering at defects is investigated through a number of different methods. If the discontinuity lies in a cross-sectional plane of the waveguide, e.g., for cracks perpendicular to the axial direction, the modal decomposition method can be applied [6,25,26]. For more complex damage geometries, a combination of finite element (FE) and boundary element techniques is suitable (e.g., see Ref.…”

“…However, these waves are also affected by other geometrical features in the structure, such as stiffeners. For the successful application of wave-based methods in defect detection and characterization, the quantitative features of these interactions need to be wellunderstood [3][4][5][6].…”

Ultrasonic Methods

“…It was also observed by various research groups that Lamb wave scattering at the beginning and tip of defect is determined by its position. Schaal et al estimated frequency-dependent scattering coefficients for fundamental Lamb wave modes at both ends of the defect (Schaal et al 2017). Based on this approach, Hu proposed a technique to locate delamination defects based on reflection and transmission coefficients of A 0 and S 0 modes (Hu et al 2008).…”

Contribution of Lamb wave modes in the formation of higher order modes cluster (HOMC) guided waves

“…Most conventional ultrasonic testing techniques utilized for testing plate-like structures take advantage of Lamb waves in one way or the other. [1][2][3][4] Lamb waves are guided waves that follow the boundaries of plate-like structures and can travel long distances without noticeable damping. 5 Lamb waves are dispersive, which means that their velocity is a function of frequency.…”