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Description
Fibre Metal Laminates (FML) constitute an advanced composite material class that combine the strength and ductility of metals with the lightweight and high-stiffness properties of fibre reinforced polymers, and thus become a promising material system for applications in aerospace, automotive engineering, and other engineering fields. Structural Health Monitoring (SHM) using Guided Ultrasonic Waves (GUW) represents a state-of-the-art approach for the non-destructive testing of such engineering structures.
When applied to FML, SHM is of key importance in assessing structural integrity over time and detecting potential damage such as delamination, fibre breakage, or other structural inhomogeneities. In SHM involving GUW, actuators emit a wave-field that interacts with structural inhomogeneities due to a change in the acoustic impedance. These interactions can lead to reflections, scattering, and mode conversion of the wave-field, which can be measured by sensors, enabling damage detection.
In this study, a central aspect involves the embedding of sensors within the laminate structure to facilitate damage monitoring in the middle layers of FML and thus enabling more advanced and precise monitoring capabilities compared to conventional measurement techniques, e.g. laser vibrometry (LSV). The embedded sensors are, unlike LSV, not limited to the measurements of deflections on the external surface of the structure. Depending on the damage type, wave modes can occur that do not cause deflection on the external surface and therefore cannot be measured with LSV. However, embedded sensors can be considered as inhomogeneity and lead to interactions with the wave-field. Analogous to damage, disturbances caused by embedded sensors will be measured by other sensors and thus can be misinterpreted as damage.
In previous research, the incorporation of an artificial interphase to match acoustic \linebreak impedances between sensor and FML showed a reduction of wave-field disturbances for anti-symmetric modes. In FML, GUW form so-called Lamb waves, which occur with different wave modes. Based on the previous work, the current study extends the concept not only for the anti-symmetric A0-mode, but also for the symmetric S0-mode.
This contribution presents a comprehensive numerical study of a two-dimensional FML model with embedded sensors. The implemented interphase is enhancing signal transmission while minimising unwanted reflections. The study explores various interphase configurations across a broad frequency range, demonstrating improved sensor integration for more accurate and reliable SHM systems. These findings offer a valuable basis for future experimental validation and the development of advanced FML structures with embedded sensors.
