Augmented Acoustic Black Holes : conception of light, stiff and non-resonant pannels – eTNAA
The design of lightweight, stiff and highly damped panels is an important issue in mechanical engineering (for aeronautical and aerospace applications for example). Composite and architected materials are some answers to this problem. The insertion of acoustic black holes (ABH), which are vibration wave traps based on local heterogeneity of stiffness and damping, is an innovative method that induces passive absorption of vibrations without adding mass. The objective of the project is to push the current limits of this strategy by developing Acoustic Black Holes, whose damping properties are enhanced in an active way. The Enhanced ABH are using active piezoelectric and thermal systems and are organized in a periodic lattice. The periodically organised panel, called meta-plate combines 4 complementary effects: damping by geometrical ABH, active control of the local stiffness, thermal control of the damping, effect of band gap induced by the periodicity of the medium.
An Acoustic Black Hole embedded in a thin walled structure consists in a tapered indentation of power-law profile, covered by a thin visco-elastic layer. Such local variations of the bending stiffness and surface density leads to a gradually decreasing phase velocity and a gradually increasing local loss factor towards the ABH center, which leads to to an efficient damping mechanism. This type of passive control of vibration is characterized by a low reflection coefficient above a cut-off frequency and by trapped modes below this cut-off frequency. The performances are limited in three ways: 1 / by the difficulties of controlling the local damping at the TNA end, 2 / by the residual thickness at the end which makes the flexural rigidity and the phase velocity non-zero; / by the existence of a cut-off frequency below which the TNA effect is ineffective.
We propose to use a shape memory polymer as absorbing layer. The elastic Young's modulus and the loss factor of this material are highly dependent on the temperature, which allows us to control them using an imposed thermal condition in order to push limit 1/. Local active control of vibration (based on the insertion of a piezoelectric patch, shunted by a negative capacity) is a way to decrease the local bending stiffness. It is precisely the targeted effect at the center of the ABH and the eigenfrequencies of the first trapped mode can thus be controlled (see limit 2 /). Considering the thermal and piezoelectric controls, the ABH is an Enhanced ABH, which can used in a cell in a plate and organized periodically to take advantage of the Bragg band gaps and the resonance band gaps which can occur. The opening of a complete band gap in a low frequency range results from a precise tuning between the ABH trapped mode eigenfrequency and the Bragg frequency of the lattice. A band gap can then occur at low frequency, below the TNA cut-off frequency, which makes it possible to push the limit 3 /.
Generally speaking, lightening a structure leads to an increase of the vibration. The ABH strategy is a way to design light and non resonant panels. The aim of the project is to design, to model, to optimize and to characterize experimentally a meta-plate of a new type, mixing 4 physical effects, in order to make the structure non-resonant, while retaining high Static stiffness and light weight.
Monsieur Francois Gautier (Laboratoire d'acoustique de l'université du Maine)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
FEMTO-ST Franche-Comté Electronique Mécanique Thermique et Optique- Sciences et Technologies
LTDS - CNRS Laboratoire de tribologie et dynamique des systèmes
LAUM Laboratoire d'acoustique de l'université du Maine
Help of the ANR 384,588 euros
Beginning and duration of the scientific project: - 48 Months