Characterizing the Poroelastic Time Scale of a Poroviscoelastic Medium using Indentation Tests

The mechanical response of a poroviscoelastic material results from the solid matrix’s viscoelasticity and poroelasticity of the fluid-filled material. Disentangling these coupled phenomena experimentally is a significant challenge. This study presents a method to quantify the associated time scales separately using indentation tests on artificial poroviscoelastic materials. Our approach involves a two-stage experiment on a custom-made porous polydimethylsiloxane (PDMS) sample. First, indentation is performed on the dry sample, and the resulting force-relaxation curve is fitted to a Generalized Maxwell model to map its intrinsic viscoelastic time scales. Second, the test is repeated with the sample saturated with a fluid. Analysis of this new relaxation curve reveals the additional poroelastic time scale. This poroelastic time scale is validated through independent measurements of the material's longitudinal modulus and its permeability via separate uniaxial compression and pressure-driven flow tests. The experimentally determined poroelastic time scale agrees within 10% with the value predicted by linear poroelastic theory using independent measured parameters. This method has been successfully applied to several different artificial poroviscoelastic samples. The framework provided by this study can be expanded to the application to fluid-saturated materials without the need for a dry reference sample.