This paper presents the experimental determination of permeability for unidirectional in-plane flow through a thin layer of nonwoven porous textile subjected to various rates of compression. The experiments were made on an original device that allows the variation of porous layer compression and pressure differential. The permeability was calculated assuming the validity of Darcy law and, in parallel, Darcy-Forchheimer model. The preliminary results obtained with water show that pressure gradient does not influence sensibly the resistance to flow of the material and Darcy’s law is applicable. For permeability-porosity correlation the experimental results were fitted using the well-known Kozeny-Carman equation. Also good correlation was found with other two models derived from Kozeny-Carman.

Based on the analysis of existing collective shockwave protection methods worldwide, this paper addresses the mitigation of shock waves by means of passive methods, namely the use of perforated plates. Employing specialized software for numerical analysis, such as ANSYS-AUTODYN 2022R1^®, the interaction of shock waves with a protection structure has been studied. By using this cost-free approach, several configurations with different opening ratios were investigated, pointing out the peculiarities of the real phenomenon. The FEM-based numerical model was calibrated by employing live explosive tests. The experimental assessments were performed for two configurations, with and without a perforated plate. The numerical results were expressed in terms of force acting on an armor plate placed behind a perforated plate at a relevant distance for ballistic protection in engineering applications. By investigating the force/impulse acting on a witness plate instead of the pressure measured at a single point, a realistic scenario can be considered. For the total impulse attenuation factor, the numerical results suggest a power law dependence, with the opening ratio as a variable.

Soft, porous structures imbibed with liquids have good impact attenuation properties. Literature survey reveals a continuous need for new impact tests to assess impact response for the newly developed soft, porous materials. This paper presents a versatile drop tower tester which is based on an impactor that slides inside a transparent tube. The test rig is equipped with high-speed transducers (force and acceleration) and a laser system used to measure the deformation of the experimental cell. A high-speed camera records subtle details of the impact that are not are visible with the naked eye. Preliminary experiments made on dry and imbibed soft fibrous tridimensional textile have shown good repeatability during impact. The experiments presented validate the experimental procedure, based on the analysis of the contact force-displacement curve, acceleration, and impact force-transmitted force. The obtained results demonstrate that true impact response is described with high resolution.

The paper presents experimental and theoretical results for the planar squeeze flow of a finite volume of viscoplastic material through a highly deformable porous layer. The central zone of an annular disc made of a reticulated polyurethane foam with high porosity (ε > 0.97) was fully filled with tooth paste. The porous disc placed between two flat, impermeable, parallel, and rigid discs was subjected to compression and the normal force was recorded. After compression, the radial extension of the squeezed fluid was measured. The visualisation of the compressed disc managed to provide evidence of a tortuous flow inside the porous structure. An original analytical model is proposed for the prediction of the front of the flow inside the porous layer and corresponding resistant normal force. The model combines the Covey and Stanmore (1981) model for squeeze flow of a Bingham fluid inside the central zone, with an original approach for flow through the reticulated foams, based on the concept of “equivalent flow tubes” with variable tortuosity. This explorative investigation is of interest for innovative shock absorbers. The model validity covers both low and high plasticity numbers and was experimentally validated for low speed.

The primary objective of this work is to provide new solutions to increase impact protection, using a three-dimensional textile imbibed with a shear-thinning fluid. An extensive analysis showed a scarcity of research papers related to the damping capacity of deformable porous materials imbibed with non-Newtonian fluid. No studies were found for shear-thinning fluid flow inside highly compressible foams or other soft, porous materials. The damping capacity of the imbibed material was evaluated using impact with a dropping weight. Polyvinyl alcohol solution mixed with water was used for imbibition of a three-dimensional textile. Hydrophilized carbon nanofibers were also added to the solution to augment the shear-thinning behavior. The measured impact force for imbibed samples showed an important reduction compared to the impact force for the dry material. This research does not focus on flow phenomena at the microstructural level but instead aims to highlight the macroscopic attenuation effect that occurs during the compression of the imbibed material.