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Effects of material and 3D printing technology on the properties of auxetic structures
Kuchtová, Štěpánka ; Žídek, Jan (referee) ; Jančář, Josef (advisor)
This thesis deals with the behaviour of auxetic structures. In particular, the focus is on the effect of the 3D printer, material filament and number of unit cells on the deformation response of auxetics. Specimens were prepared on two printers with a direct and a bowden extruder made of PET-G (polyethylene terephthalate glycol) and TPU (thermoplastic polyether polyurethane) materials. The prepared structures were subjected to a static compression test, during which video recordings were taken. From the video recordings the Poisson's ratio and porosity of the samples were subsequently evaluated. A software application was written in Python programming language to evaluate the Poisson's ratio and porosity. The type of 3D printer had a significant effect on the properties of the prepared auxetic structures. The specimens prepared by the bowden extruder printer exhibited lower stiffness and yield strength and higher Poisson's ratio compared to the samples prepared by the direct extruder printer. Furthermore, the influence of the number of unit cells and influence of the material with low (TPU) and high (PET-G) elastic modulus on the auxetic behaviour was investigated. In the case of the flexible material, specimens with fewer unit cells exhibited tougher response, whereas the opposite was true for PET-G. At the same time, attention was paid to the deformation response of single cells within the sample, where TPU exhibited a different deformation behaviour mechanism than PET-G. This has been reflected in different spatial distribution of auxetic behaviour within the specimens.
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