Dynamic compression of soft porous media: From finite to infinite domain

In recent studies about lift generation in porous media, dynamic compression experiments have been performed using a porous-walled cylinder-piston apparatus, where the air trapped inside a porous layer underneath the loaded piston was forced out through the porous wall to the ambient, namely, "finite domain," oversimplifying real applications where transiently trapped fluid is squeezed out to the surrounding porous structures, that is, "infinite domain." In the current paper we treat this shortcoming experimentally. A soft, polyester, fibrous, porous material was chosen for the study. Its microstructure was characterized using a scanning electronic microscope. Its porosity was measured using a water-displacement method, and its permeability was determined using a permeameter. The cylinder-piston apparatus was first used in a quasi-static experiment to examine the material's stiffness and was then used in the dynamic compaction experiments in the infinite domain. Detailed pressure distribution was examined. The results indicate that the air lifting force is enhanced by 25 to 30% for the infinite domain over the finite domain due to the existence of the surrounding porous material. The pore pressure, however, relaxes rapidly in the undeformed surroundings. These observations improve our understanding of the dynamic response of soft porous media under rapid compression.