Experimental validation of analytical models for nonacoustic properties of loose fibers

The characterization of materials is an important part of the process for the development of NVH packages in the automotive industry. In particular, fibrous materials for acoustical applications have been extensively studied over the past years and a considerable number of experimental tests have been carried out as a function of fiber geometrical characteristics (for example, bulk density, fiber diameter and density, open porosity, etc.) in order to determine analytical formulations for the prediction of physical parameters. The type of components under investigation in this study are made from recycled fibers, both natural and manmade. Due to the random nature of the mix of individual fibers, which can include different densities and thicknesses, predictive models normally do not take into account the individual fibers but instead deal with the mixture as a whole. This paper examines an ongoing study into the experimental characterization of individual fibers (in terms of airflow resistivity, open porosity, tortuosity, characteristic lengths and static thermal permeability) and the validation of new analytical models (as a function of open porosity and fiber radius) that will help in the determination of overall acoustic performance.