In this study, fully recyclable and elastic–plastic deformable sandwich panels were developed by considering the mass production requirements, as well as the lightweighting needs of the automotive industry. Expanded polypropylene (EPP) foam core and self-reinforced polypropylene (PP) thermoplastic composite face sheets were selected to produce sandwich panels. Three-point bending experiments were performed to obtain the flexural behavior of the sandwich panels. Finite-element analysis (FEA) of the sandwich beams was carried out and confirmed by experimental results. Three different EPP foam cores with densities of 65.7, 36.5 and 27.0 kg/m3 were used. The FEA models were built in the Abaqus commercial software in three-dimensional (3D) space, and analyses were performed using 3D elements. The crushable foam material model was selected for FEA from the Abaqus material model database to obtain the best correlation with the foam compression test results. The force–displacement results of the three-point bending FEA results excellently correlated with the experiments. In three-point bending experiments of the sandwich panels, elastic–plastic deformation of the core with indentation failure was observed. The lowest-density foam core sandwich beam showed the highest deformation and energy absorption performance. Also, deflection recovery was observed after load removal for all sandwiches.

Auxiliary metamaterials designed according to the Negative Poisson’s Ratio (NPR) property are exciting structures due to their high impact strength, impact energy absorption abilities, and different damage mechanisms. These good mechanical features are suitable for aviation, automotive, and protective construction applications. These structures, whose most significant disadvantages are production difficulties, have become easier to produce with the development of 3D production technology and have been the subject of many studies in recent years. In this presented study, two conventional core geometries and three different auxetic geometries, commonly used in sandwich structures, were designed and produced with 3D printer technology. The strength and energy absorption capabilities of prototype sandwich structures investigated experimentally under bending loads with static and dynamic compression. Except for the re-entrant (RE) type core, the auxetic core foam sandwich structures demonstrate higher rigidity and load-carrying capacity than classical sinusoidal corrugated (SC) core and honeycomb (HC) core sandwich structures under both quasi-static and impact-loaded compression and three-point bending experiments. Double arrowhead (DAH) and tetrachiral (TC) auxetic cores outperformed honeycomb core in terms of specific quasi-static and impact load-bearing performance under compression by 1.5 ± 0.25 times. In three-point bending experiments under both quasi-static and impact loading conditions, the load-carrying capacity of the double arrowhead and tetrachiral auxetic cores was found to be more than 1,86 ± 0.38 times that of the honeycomb core sandwich panels.

In this study, the impact behavior of sandwich panels of natural rubber-based syntactic foam cores with aluminum face sheets was investigated experimentally and with the help of finite element analysis (FEA). Syntactic foam cores were produced byadding glass bubbles (GB) to the natural rubber (NR). Natural rubber was dissolved at room temperature with chemical solvents mixed with glass bubbles at 10, 20, and 30 weight percentages. Very low density (~0.8 g × cm-3) and high compressible foams were obtained depending on the GB weight percentages. Aluminum face sheets and the NR/GB syntactic foam core developed were joined by adhesive bonding to produce sandwich beam specimens. The sandwich beams manufactured in this way were subjected to impact loading under three-point bending boundary conditions experimentally. The experimental results were compared with finite element simulation results under the same loading and boundary conditions. The damage mechanism of the sandwich panels devised were analyzed. According to the results, natural rubber containing an additive of 20 wt.-% GBs showed better impact resistance than the others.

In this study, two different foam core aluminum face sheets sandwich panels were developed. The core materials were selected as expanded polypropylene (EPP) and extruded polystyrene (XPS) foams. Two aluminum face sheets and foam cores were combined with flexible epoxy-based adhesives, under 20 N static compression load. The average density of the produced sandwich panels was 0.39 g/cm 3 for EPP foam core sandwich and 0.33 g/cm 3 for XPS foam core sandwich panel. Produced specimens were subjected 3-point bending experiments under impact loading. Damage behavior of the sandwiches was observed using post-mortem pictures. The results show that the produced sandwiches damaged perfectly plastic deformations with face sheets and core. There was not any adhesive and cohesive failure in the core and face sheets interfaces.

Due to the developing electric vehicle industry in the last decade, weight reduction studies on vehicle bodies have gained great importance. Foam core sandwich structures stand out as the most ideal materials in terms of providing both weight reduction and strength conditions in the bodies of electric individual and public transportation vehicles. In this study, EPP foams with two different densities were placed between aluminum plates and sandwich structures were obtained by combining the two structures with an EVA-based adhesive. Compression and bending behaviors of the produced sandwich structures were investigated under quasi-static and dynamic loading conditions. With the tests carried out, the strength of the sandwich structures and the amount of energy they absorb were calculated and compared experimentally. According to the results obtained, it was observed that the denser D2 foam exhibited approximately 1.4 to 2.05 times more strength than the lower density D1 foam in all tests. In terms of the energy they absorb, the D2 foam absorbs 1.25 to 2.5 times more energy than the other foam. Contrary to this situation, only the dynamic compression test occurred in the tests performed. When the post-damage behavior of the sandwich structures was examined, it was also observed that the D2 foam returned to a very similar dimensions to its original size, giving more of the deformation after the damage at the end of 72 hours.