Enhancing the flow resistance and sound absorption of open-cell metallic foams by creating partially-open windows

Metallic foams with high flow resistivity are of high interest as practical sound absorption materials. Herein, we report the novel open-cell metallic foams associated with a partially-open window morphology between interconnected pores for improved flow resistivity and sound absorption coefficient. Such a microstructure was produced through exploiting the shear thinning behavior of the metal slurry during the template replication fabrication process. A new microstructural model for permeability simulation is also developed for the new foam to account for the increased specific surface area from the windows. Input parameters to the model include cell geometries that are accessible via morphological characterization. Results showed that metallic foams with the window morphology have significantly increased flow resistivity (1.5 times) with little loss in porosity (< 2.3%). Impedance tube acoustic measurements confirmed such increments to improve the sound absorption coefficient (averaged as 0.2) throughout the entire frequency range. The concept explored in this study demonstrates a generic approach for the design of microstructure-specific foams with simultaneously increased flow resistance and a fully open-celled microstructure associated with high porosity (between 93%~97%). The proposed fluid model also has excellent potential to be adopted in a diverse range of applications for design and characterization.