| Περίληψη: | Cellular structures, such as lattices and honeycombs, have proved to be satisfactory for their applicability due to their outstanding properties, such as high strength, absorbed energy, lightweight design, and reduced vibration, which have been extensively studied and concerned. Because of their excellent properties, cellular structures have been widely used in aviation, aerospace, bioengineering, automation, sport, and other industrial fields. Nowadays, with the development of Additive Manufacturing (AM) technology this concept can easily be exploited and change the conventional material world, as it offers a design freedom so that complex geometries with the desired mechanical properties can be manufactured. Honeycombs are well-known for their out-of-plane energy absorption capacity, but in some applications, crushing occurs along any direction of the honeycomb. Therefore, it is important to enhance their in-plane behavior and techniques like foam filling and variation of the density through the structure are lately investigated. After a comprehensive literature review, we concluded that the performance of Nylon12 honeycombs have not been broadly explored, although it is a very promising lightweight material which can be used to 3D printing the structure. Thus, in this thesis we aim to investigate the performance of a Nylon 12 hexagonal honeycomb. A verification of the finite element (FE) model is conducted by comparing the results with published experimental work. The influence of the honeycomb’s size on its performance was, also, studied. In consequence, to enhance the energy absorption (EA) of the Nylon12 hexagonal honeycomb the density of the structure is distributed, by changing the thickness of each cell wall, while the overall density remained equal to the initial uniform structure. Specific gradients led to the higher densification strain, increased specific energy absorption (SEA) and lower initial loads, while others to the opposite. Moreover, the honeycomb was filled with Rohacell foam of different densities, and it was found that the SEA increase up to 150%, while the density only a small portion 41%, but the initial loads increased, too. Finally, a structure which combine the aforementioned techniques is modeled and the results showed the highest increase of the SEA compared to the other two methods and lower initial loads. The FE models of all the three techniques were parameterized with a MATLAB code and the results were processed saved for future use.
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