Effects of shear thickening fluid filling in additively manufactured sandwich panels during intermediate and high strain rate penetration

Abstract

Along with metal foams and lattices based on various unit-cell architectures, sandwich panels have become a prospective solution to problems involving deformation energy mitigation. The combination of a face sheet and a porous core in the sandwich panel exhibits synergistic effects in its effective properties, which has attracted attention in the field of dynamic impact and blast perforation. Further advances can be inspired by the performance of interpenetrating phase composites (IPPCs). These novel meta-materials consist of two or more topologically continuous and three-dimensionally interconnected phases, where the matrix is reinforced by the microstructure of a foam or lattice. Using a combination of IPPC with a sandwich panel architecture based on a suitable filling material, it is possible to further enhance the specific deformation mitigation characteristics of the panel with respect to the strain rate dependence. Here, shear thickening non-Newtonian fluids (STFs) are a type of filling with the potential to greatly enhance the performance of sandwich panels in comparison to Newtonian fluid filling materials. In this paper, we investigate STF (polyethylene glycol with hydrophilic fumed silica) filled sandwich panels with an additively manufactured periodic core subjected to dynamic penetration at an intermediate and a high strain rate. Intermediate strain rate loading (maximum impact velocity of 2 m s${}^{-1}$) is induced by a loading apparatus based on linear motors. The high strain rate loading is carried out using a direct impact Hopkinson bar (DIHB) apparatus at impact velocities of 10 m s${}^{-1}$ and 20 m s${}^{-1}$. Both types of experiments were amply instrumented by high-speed cameras and in-situ X-ray radiographical imaging was used to reveal deformation processes within the microstructure of the panels including flash X-ray radiography of the DIHB experiments. The DIHB apparatus was equipped with a novel wireless instrumented striker recording its velocity using contactless linear encoders. To explore the potential and characteristics of such a bar velocity measurement, finite element simulations of void tests (i.e., impact experiments without a specimen) were performed in LS-DYNA and evaluated using the same methods and algorithms used to process the experimental data. A strong strain rate dependence was revealed in the impact behavior of the sandwich panels, while the contribution of the STF filling was clearly identified in both the mechanical and image data acquired during the experiments.