Measuring the dynamic shear modulus of poroelastic foams in the audible frequency range

Laurens Boeckx (1) , Philippe Leclaire (1) , Christ Glorieux (1) , Walter Lauriks (1) , Jean-François Allard (2)

1 LATF - Laboratorium voor Akoestiek en Thermische Fysica
2 LAUM - Laboratoire d'Acoustique de l'Université du Mans

The prediction of acoustical properties of multilayered systems including poroelastic layers using the full Biot theory is in principle possible but in practice limited by the absence of material data. One of the parameters that is difficult to measure is the dynamic rigidity of the porous frame. Current experimental methods are limited to the lower part of the audible frequency range 1 (typically below 400 Hz) and require special shapes of the sample (cube, cylindrical rod or very thin samples). Since most sound absorbing plastic foams are viscoelastic, the elastic moduli may vary strongly with frequency, a measuring technique in the full audible frequency range is needed. Recently, a new method for the measurement of the dynamic shear modulus of the frame of poroelastic foams in the medium and high audible frequency range (1 to 4 kHz) has been presented This method is based on the measurement of the velocity and the damping of a Rayleigh-type surface wave on sample with thickness larger than the Rayleigh wave penetration depth. The Rayleigh wave was excited through direct mechanical excitation of the frame or the porous material and detected using a laser-doppler vibrometer. The velocity of this wave is closely related to the shear velocity, which is directly linked to the shear modulus. The damping of the Rayleigh wave can be used to determine the imaginary part of the shear modulus. In this work a first attempt is made to measure the dynamic shear modulus on a layer of finite thickness. In this way there is no requirement whatsoever concerning the shape of the sample under investigation.

Domaines: Acoustique [physics.class-ph]

Laurens Boeckx, Philippe Leclaire, Christ Glorieux, Walter Lauriks, Jean-François Allard. Measuring the dynamic shear modulus of poroelastic foams in the audible frequency range. 18th International Congress on Acoustics (ICA2004), Acoustical Society of Japan, Apr 2004, Kyoto, Japan. ⟨hal-01329877⟩