Vibration damping of fiberglass honeycomb sandwich panels based on the acoustic black hole effect

Abstract

An Acoustic Black Hole (ABH) is a scatterer, embedded in a panel, allowing passive vibration control without adding mass. In practice, it is achieved by means of a local reduction in thickness (axisymmetric pit with a parabolic profile) and the addition of a thin viscoelastic coating in a central region of uniform thickness (plateau). The vibration absorption induced by the ABH, enables the design of stiff, light and non-resonant panels. In this paper, a study of the ABH effect for a sandwich panel made of a honeycomb core and fiberglass skins, which gives rise to both bending and shear effects is conducted. In particular, it is shown that the equations of motion of the thick, symmetrical sandwich panel with variable characteristics is obtained within the framework of the Nilsson’s theory. These equations lead to a sixth-order analytical model that is used to determine the dispersion curves of the sandwich and also to establish an analytical model of the ABH inserted in a sandwich panel. Experimental tests postproceed by two complementary inverse methods are used to characterize the sandwich’s mechanical properties. In particular, the model powered by experimentally determined parameters is used to analyze the effect of shear on the ABH effect, and to demonstrate that shear-induced softening is beneficial to ABH-induced absorption.