Investigation of mechanical properties of honeycomb hybrid materials

Lightweight polymer foams and aluminium honeycomb materials with high strength and energy absorption capacity are significant two members of cellular materials. The importance of using these materials as a hybrid is increasing in various critical industries such as aviation, defense, biomedical, and transportation. In this thesis, in-situ EVA foam-filled aluminum honeycomb hybrid materials with different cell sizes, foil thicknesses, and heights were produced. The effects of EVA foam on mechanical properties were investigated by comparing it with unfilled honeycomb specimens with the same geometrical parameters. According to the results, EVA filling which is foamed at certain parameters such as temperature, and time showed a strong interaction between aluminum cell walls. In-situ EVA foamed aluminum honeycombs showed spring-back characteristics thanks to their thermoplastic nature. EVA foamed sample with 14.17 mm cell size, 50 µm foil thickness, and 6 mm height showed 70% temporary recovery after compression force was removed. In addition, it is obtained that bigger cell size of honeycomb lead to higher spring back ratio. In this study, the effects of geometrical parameters of honeycombs on characteristics obtained from compression test such as peak strength, critical strain, plateau strength, and densification strain were investigated. Peak strength and plateau strength decreased as cell sizes increased. Peak strength also increased as the foil thickness of aluminum was increased. The maximum load-carrying capacity and plateau strength of the structure also increased thanks to EVA foam filling. The most efficient parameter was obtained as the t/l ratio which is the ratio of foil thickness and free wall length for mechanical properties of both filled and unfilled structures. It is determined that plateau strength, peak strength, and absorbed energy per unit volume increased when t/l ratio increased. Moreover, the impact behavior of unfilled and EVA foam-filled samples with the highest t/l ratio was investigated under dynamic conditions via the drop weight test. Thermogravimetric analysis (TGA) and differential scanning calorimeter (DSC) were used for the optimization of EVA foam production. Micro observations of damaged specimens after compression tests were done via scanning electron microscope.