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Improving the strength of additively manufactured objects via modified interior structure

AL, Can Mert
Yaman, Ulaş
This thesis study provides an approach to improve the durability of additively manufactured parts via modified interior structures by considering the stress field results from tensile loading conditions. In other words, the study provides an automated method, i.e., implicit slicing method, which improves the strength of the parts with infill structures modified according to the quasi-static Finite Element Analysis (FEA) results under tensile loadings, automatically. The parts which are used throughout the work are designed by using Rhinoceros3D® which is Computer Aided Design (CAD) software by considering the ASTM D638 standard. In scope of this study, the interior structures of the designed parts are modified by using the developed algorithm in Grasshopper3D® , which provides the strength improvements by the help of heterogeneous infill structures. The quasi-static FEA is performed in Karamba3D® which works as a plug-in on Grasshopper3D® . Interior structures are constructed by using the stress field results and the first principal stress vector directions under the tensile loading conditions. The G-Code file which is required to manufacture the parts via 3D printing is also obtained inside the constructed Grasshopper3D® schema by using a Python scripting to be used for a DeltaWASP 3D printer. For the geometries, different methods were employed to construct the interior structures. Then, the method which gives the most durable parts was applied for different parts to prove the applicability of the approach. The tensile tests were performed by using the ASTM-D638 tensile testing standard. The first version of the developed method was a kind of manual method. By using the proposed manual algorithm, the durability of the standard part was increased by about 42%. Regarding the further steps of this thesis study, the method used to construct the infill structure was tried to be automated. In this automated method, the only input is the designed geometry. The method itself obtains the boundaries of the colored meshes, fills the interior of the regions according to their colors by using the lines which connect the first principal stress vectors and generates the G-code file to be submitted to an open source Fused Deposition Modeling (FDM) 3D printed for fabrication. By using this automated algorithm, the ultimate tensile strength of the parts was increased by about 50%. The maximum load per weight ratios of the more complex geometries are improved by about 85%.