Sound Absorbent Material Made of Natural Hollow Milkweed Fibers
Simon Campeau, Raymond Panneton, Saïd Elkoun
|Inverse Poroelastic Characterization of Open-cell Porous Materials Using an Impedance Tube
Kevin Verdiere, Raymond Panneton, Noureddine Atalla, Saïd Elkoun
June 12-15, 2017
Conference and Exhibition on Noise and Vibration
A poroelastic characterization of open-cell porous materials using an impedance tube is proposed in this paper. Commonly, porous materials are modeled using Biot’s theory. However, this theory requires several parameters which can be difficult to obtain by different methods (direct, indirect or inverse measurements). The proposed method retrieves all the Biot’s parameters with one absorption measurement in an impedance tube for isotropic poroelastic materials following the Johnson-Champoux-Allard’s model (for the fluid phase).
The sample is a cylinder bonded to the rigid termination of the tube with a diameter smaller than the tube’s one. In that case, a lateral air gap is voluntary induced to prevent lateral clamping. Using this setup, the absorption curve exhibits a characteristic elastic resonance (quarter wavelength resonance) and the repeatability is ensured by controlling boundary and mounting conditions. The inversion algorithm contains a global optimization process using an axisymmetric finite element code implemented in the FOAM-X characterization software. To apply the inversion, the user must provide tube diameter, together with sample diameter, thickness, density, and absorption curve. Also, when available, some other parameters can be provided, such as open porosity, airflow resistivity, tortuosity, or Poisson’s ratio. Providing these additional parameters improves the algorithm convergence. The algorithm is tested on different porous materials and compared to direct measurements. For some materials, the main experimental challenge is to make sure to excite the elastic resonance during impedance tube measurements. Once the resonance is excited, the proposed inversion algorithm finds Biot’s parameters that are generally comparable with direct measurements. The validity and main limitations of the method are finally discussed.
Acoustics of porous materials: Experimental techniques
Open-cell porous materials are used for soundproofing and noise control. Engineers simulate their performance in different applications using state-of-the-art prediction software. To define these materials, up to ten (10) material properties are required following the Biot-Allard poroelasticity model. There are 6 non-acoustical parameters (open porosity, static airflow resistivity, tortuosity, viscous and thermal characteristic lengths, static thermal permeability), 1 physical property (in-vacuum bulk density) and 3 viscoelastic properties (Young’s modulus, Poisson’s ratio, damping loss factor). This workshop is on the experimental techniques and good practices to accurately characterize the porous material properties
Noise control materials: Characterization and modeling
Noureddine Atalla, Raymond Panneton
Part I of this workshop addresses the analytical and numerical modeling of multilayered panels made up from different materials, notably open-cell porous materials. Also, many acoustic treatments are modeled, and their predictions compared to experimental measurements under normal incidence and diffuse field measurements.
Part II addresses the characterization of noise control treatments, and most particularly the porous materials. Direct and inverse measurement methods are presented, and the main challenges of the characterization of real material samples discussed. Also, the material parameters of a numbers of materials are characterized, and their accuracy validated.