Prediction of the sound absorption behavior of nonwoven fabrics: Computational study and experimental validation

Abstract

Prediction of acoustic characteristics of porous media from the microstructure is the first step in designing novel materials with enhanced acoustic properties. This paper aims to provide insights into the microstructure of nonwoven fabrics and demonstrate how it collectively dictates their acoustical macro-behavior. To this end, fibers of different fineness were spun on an industrial-scale compact melt spinning line. Fibers were then fed into a laboratory needle punching line to produce nonwoven fabrics. Microstructural properties of fabrics were obtained using morphological analysis of their 3D realistic images obtained using X-ray micro-computed tomography (µCT). The sound absorption coefficient (SAC) of samples was measured using a two-microphone impedance tube. Moreover, to investigate the effect of fabric microstructure on sound absorption behavior, virtual fibrous structures with different thicknesses, porosities, fiber diameters, and through-plane fiber orientations were simulated. Fluid resistivity was calculated by simulation of airflow through the microstructure of generated virtual structures and solving the Stokes equations. Finally, the sound absorption spectrum of nonwoven fabrics was predicted using the empirical model of Delany-Bazley-Miki, and the results were compared with experimental data. Very good agreement was observed between the results of the proposed model and the experimental data. The results indicated that for samples with the same porosity of 91% and fiber diameter of 16 µm, an increase in fabric thickness up to 2 cm leads to an increase in SAC, while further increase in thickness does not improve SAC at high-frequency bands. Moreover, with increasing fabric thickness, the SAC peak shifts from the high-frequency range to the low-frequency range. It was found that for samples with a thickness of 3 cm, decreasing fiber diameter from 32 µm to 16 µm enhances SAC at low- and medium-frequency ranges, while a further decrease in fiber diameter adversely affects the SAC. It was also found that there is an optimal porosity for a nonwoven fabric in view of maximizing its sound absorption performance. The results indicated that SAC decreases with decreasing the angle between the dominant fiber orientation and sound incidence direction. It was concluded that 3D uniform isotropic samples exhibit the highest SAC.