Guided wave characteristics in the functionally graded two-dimensional hexagonal quasi-crystal plate

Due to the limit of preparation technology, defects, such as cracks and inclusions, are inevitable in the functionally graded quasi-crystal material. For the purpose of the guided wave non-destructive testing on the functionally graded (FG) two-dimensional(2-D) hexagonal quasi-crystal(QC) plates, Lamb and SH wave characteristics in the context of the Bak's model are investigated by means of the Legendre polynomial method. The convergence of the polynomial method applied on the FG 2-D hexagonal QC plate is analyzed. Some new wave characteristics resulted from the phonon-phason coupling effect are revealed. There are three Lamb-like modes without cut-off frequencies for the x-y and y-z QC plates, but four Lamb-like modes without cut-off frequencies for the x-z QC plate. For phonon modes, phonon displacements and stresses are bigger than phason displacements and stresses. However, they are just opposite for phason modes. It can be utilized to distinguish phonon modes and phason modes.