Identification of impact events in sandwich structures is extremely challenging,because wave propagation in them can be highly complicated due to the interplaybetween facesheet and core materials. This becomes more evident when sandwichstructures are exposed to harsh mechanical and/or thermal environments, whichprevent the installation of sensing suites on their external surfaces. Therefore,conventional structural health monitoring techniques based on guided Lamb wavesand their triangulations can often yield inaccurate and unreliable diagnostic outcome.To overcome this challenge, a novel diagnostic approach is proposed based on highlynonlinear solitary waves. Solitary waves are compactly-supported energy packets,which are generated by a balance of nonlinear and dispersive effects in nonlinearmedia, such as granular crystals. In this study, we fabricate a sandwich structure with athick core that embeds arrays of granular crystals. Upon the external impact on thefacesheet, granular crystals transfer energy and momentum of Lamb waves to highlynonlinear solitary waves. The solitary waves are recorded in real-time using embeddedpiezoelectric discs positioned at the tip of granular crystals. Based on the measuredtime-of-flights and disintegrated mode shapes of the solitary waves, we identify thelocation of impact on sandwich structures. The proposed granular crystal-basedsensing system has a potential as an effective impact monitoring tool for inspectingstructural damages in critical areas of sandwich structures under harsh environments.
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