Damping of flexural vibrations in composite plates and panels containing one- and two-dimensional acoustic black holes

In this paper, the results of the experimental investigations into the addition of one-dimensional and twodimensional acoustic black holes into composite plates and their subsequent inclusion into composite panels are reported. The composite plates in question are sheets of composite with one-dimensional or two-dimensional indentations of power-law profile materialising acoustic black holes for flexural waves. A panel is a sheet of composite with the indentations encased within the sample. This makes a panel similar in surface texture to an un-machined composite sheet (reference plate). In the case of quadratic or higher-order profiles, the abovementioned indentations act as one- or two-dimensional acoustic black holes for flexural waves that can absorb a large proportion of the incident wave energy. For all the composite samples tested in this investigation, the addition of one- or two-dimensional acoustic black holes resulted in further increase in damping of resonant vibrations, in addition to the already substantial inherent damping due to large values of the loss factor for composites (0.1 - 0.2). Note in this connection that due to large values of the loss factor for composite materials used, no increase in damping was seen with the addition of a small amount of absorbing material to the indentations, as expected.