Introduction: Additive manufacturing, also known as 3D printing, has become a versatile technology that allows the production of three-dimensional objects by adding material layer by layer. One of the most commonly used 3D printing technology is fused deposition modelling - FDM. The printing process and the quality and properties of the printed object depend on a large number of parameters. For the mechanical properties of the 3D printed object, the most important parameters are related to the structure of the product. The main parameters are the infill percentage and pattern. In addition to the printing parameters, the choice of a suitable material is also important. Nowadays, many different materials are available for FDM technology, such as acrylonitrile butadiene styrene (ABS), polylactic acid (PLA) and thermoplastic polyurethane (TPU). Purpose: To investigate and analyze the connection between two factors, infill percentage and pattern, and the mechanical properties of a 3D printed object and to identify the optimal combination of infill proportion and pattern type that can achieve the best mechanical properties of 3D printed thermoplastic polyurethane. Methods: Test specimens were printed with varioShore TPU filament on a BlackBelt 3D printer. Infill percentages from 10% to 100% and two infill patterns, Gyroid and Zig Zag were compared. In total, fifty-two test specimens were printed. Tensile, compressive and Shore A hardness tests were carried out according to selected standards. Compressive and tensile strength, Young's modulus and elongation at break and at 20 % strain in the case of the compressive test were determined. The repeatability of the measurements was also evaluated. Results: The tensile strength of both infill patterns increased with increasing infill percentage up to 70% infill, the strength remained constant with a further increase in infill percentage. The same increasing trend was observed for Young's modulus and relative elongation. The measured hardness increased only up to about 50% of the infill, with only a slight change in hardness with further increases in the infill percentage. The maximum measured hardness was 70 Shore A at 100% for both Zig Zag and Gyroid. Higher compressive strength values were also observed at higher infill percentages. In the compressive test, the values increased with the proportion of filler up to 90% fill. For most specimens, higher values of the investigated mechanical properties were measured when using the Zig Zag infill pattern. Discussion and conclusion: We found that both infill percentage and pattern have a significant effect on the mechanical properties of 3D printed objects. Higher infill percentages generally led to higher tensile and compressive strength and hardness due to a denser internal structure. The infill pattern did not have a significant effect on hardness. The specimens with Zig Zag infill pattern showed higher tensile and compressive strength than those using the Gyroid pattern.
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