Comparison of methods for characterizing sound absorbing materials
Keywords:Elastic moduli, Porosity, Vacuum, Archimedes principle, Metal foam, Static resistivity, Thermal characteristic dimension (TCD), Viscous characteristic dimension (VCD)
AbstractA study was conducted to characterize three samples of metal foam, using direct, indirect, and inverse methods to highlight that the methods may yield large variability in the found parameters. Direct measurement of the open porosity was performed, using the Archimedes principle. It provided a direct measured value of open porosity through measurement of sample weight in vacuum, in air, and predicted the measurement error. Analytical solutions were used to determine the static airflow resistivity, tortuosity, viscous characteristic dimension (VCD), and thermal characteristic dimension (TCD) of the material, assuming that dynamic density, dynamic bulk modulus, and open porosity were known. The inverse method was applied the tortuosity and the two characteristic lengths, assuming porosity and static resistivity to be known from direct measurements. The results show that the parameter values are in better agreement from one sample to another and the deviation from mean values are acceptable.
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