Elastic wave propagation in composites
Materials science has advanced tremendously in the last 25 years, spurred on in large part by developments in nanotechnology, quantum mechanics and experimental characterisation techniques. For the design of next-generation devices, it is critical to gain in-depth understanding of material properties. Researchers addressed elastic wave propagation in structured media with EU support of the project DYNA META 11 (Controlling elastic waves: structured media and metamaterials in the mechanics of solids and structures). Scientists designed and modelled several but different high-contrast (highly non-homogeneous) semi-discrete structures. High-contrast periodic media can exhibit stop bands, gaps in the frequencies of waves that can propagate. One of the several systems studied was a locally resonant elastic metamaterial that also exhibited negative refraction of the wave trajectory. Application includes filtering (rejecting or passing only certain frequencies), reflecting, and focusing devices. Researchers then went on to develop a model of a flexural wave transmitted through a periodically supported discrete structure that was applicable to real bridges. The team also considered propagation of an edge-crack or fault in a thermoelastic lattice structure, important in safety and reliability assessment in the nuclear industry. DYNA META 11 addressed the creation of invisibility cloaks based on geometrical transforms that accounts for acoustics and out-of-plane elastic waves. Here, scientists developed transformation-based theories to assess the quality of cloaks as well as flexural deformations in thin plates. The latter showed that, in contrast to previous work, it is possible to construct an invisibility cloak for such systems with important simplifications. Finally, the team addressed optimal design of real-life slender engineering structures. In one case, scientists used their mathematical algorithms to facilitate filtering and polarisation, enabling by-pass of undesired elastic waves. The algorithm predicted the velocity of failure propagation in the fire collapse of the San Saba bridge in Texas in May 2013, very simply and with extremely high accuracy. DYNA META 11 has produced important mathematical descriptions of elastic wave propagation in structured media, including metamaterials such as cloaks. Accurate numerical simulations provided insight into real-world problems and advanced understanding of the poorly understood negative refraction in elasticity.
Keywords
Elastic wave, propagation, composite, periodic, high-contrast, metamaterial, bridge, cloak
