Tuning membrane content of sound absorbing cellular foams: Fabrication, experimental evidence and multiscale numerical simulations

This work is focused on tailoring cellular foam membranes for sound absorption. Several foam configurations with a constant porosity and varying membrane content were first fabricated by using milli-fluidic techniques. This approach allows transport and sound absorbing properties to be continuously tuned on purpose, from open-cell to closed-cell foams. The morphology of these foams was then investigated using optical micrography. Microstructural descriptors such as the proportions of closed and open windows and aperture size were specifically analyzed. The associated transport and sound absorbing properties were subsequently characterized using airflow resistivity and three-microphone standing wave tube measurements. The numerical reconstruction of foam samples was next addressed by considering a Periodic Unit Cell (PUC) approach on Kelvin cells. The transport properties of these virtual samples were determined by numerical homogenization, performing sequential evaluations of the parameters that govern visco-thermal losses. To overcome the limitation induced by the size of the numerical model at the pore scale, an averaging procedure was proposed. The results show that the PUC model can be used to accurately predict the transport and sound absorbing behavior of interest. The relevance of the multiscale estimations for acoustic properties is demonstrated over the entire range of membrane content.