Chemistry-process morphology control of porous micro-structures: a bottom-up acoustic optimization approach
Résumé
Using numerical homogenization techniques at microstructure scale, one can simulate the acoustic macro-behavior of open-cell or partially closed-cell polymeric foams, typically their absorption coefficient or transmission loss. This link is realized through the scaling of an idealized 3D Periodic Unit Cell (PUC), which represents statistically the pores shape as regular arrays of polyhedra. Based on two non-acoustic standard measurements, namely the porosity and the static viscous permeability, plus a microstructure ligament length measurement as well as solid film thickness, the 3D PUC is scaled including membranes interconnecting the pores in the actual foam morphology. The opening of these membranes, constituting partially closed windows or throats between pores, proves to be an essential microstructure optimization parameter for sound absorption and mechanical behavior. On this 3D PUC, finite element computations are carried out in order to determine the intrinsic Biot-Allard parameters of the foam, by solving asymptotically the viscous Navier-Stokes flow at low frequencies, the inertial Laplace potential flow at high frequencies, the thermal conduction at low frequencies, as well as mechanical virtual pure tensile and pure shear strain tests. This micro-macro procedure proves to give good correlation with complete non-acoustic and acoustic characterization measurements, building a new reliable optimization scheme for poroelastic foams, which will be illustrated on a polyurethane injected soft foam.
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