Interfacial delamination-induced unidirectional propagation of guided waves in multilayered media

Unidirectional nonreciprocal wave propagation is an unprecedented phenomenon, which has attracted much research interest. Connecting a phononic crystal with an asymmetric structure to break the spatial inversion symmetry is a popular manner to realize this phenomenon using the wave mode transformation. In this paper, a new model is proposed based on a single periodic structure. The arrays of asymmetric and symmetric interfacial delaminations are intentionally introduced into the top and the bottom part of a stack of periodic elastic layers, respectively. So, the structural spatial inversion symmetry can be broken and the guided waves can pass through the whole structure only from the top side with the changed mode generated by the array of asymmetric interfacial delaminations. Thus, it is indispensable for the part of phononic crystal that the partial band-gaps of symmetric and antisymmetric guided waves have to be separated, which is the reason why we introduce the array of symmetric central or side interfacial delaminations into the stack of periodic elastic layers. The transmission spectra of the guided waves and the dispersion curves for the unit cell imposed by the Bloch–Floquet boundary condition are both calculated by the spectral element method. Then, the interfacial delamination-induced unidirectional propagation of guided waves in the finite stack of periodic elastic layers is numerically confirmed. This paper provides a new concept to control the waves propagating in phononic crystals via the insertion of some interfacial delaminations or cracks.