PSI - Issue 37

Mohammad Reza Khosravani et al. / Procedia Structural Integrity 37 (2022) 97–104 Mohammad Reza Khosravani et al. / Structural Integrity Procedia 00 (2021) 000 – 000

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series of experimental practices were carried out to determine load-carrying capacity of the 3D-printed components. As manufacturing defects (e.g., voids, gaps) can significantly reduce the strength of 3D-printed polymer parts further investigation is required to determine influence of the defects on the structural integrity of the 3D-printed parts.

3. Experimental procedure 3.1. Fabrication of 3D-printed specimens

In the current study, dog-bone shaped specimens were fabricated via FDM 3D printer according to type I ASTM D638 with a thickness of 6 mm ASTM D638 (2014). It should be noted that both groups of intact and defects specimens were printed under the same printing conditions. In this respect, all the specimens were designed in a CAD platform and then saved in “.stl” format. The then files were imported to Cura TM slicing engine which is an open source program for slicing and setting printing parameters. Finally, the files were used to extrude and deposit material which is built up in layers from a horizontal base. Here, we used Timberfill Champagne filament with 1.75 mm diameter, produced by Filamentum. The nozzle diameter of the printer was 0.8 mm and printer velocity was set to 30 mm/s for fabrication of all specimens. Each layer set was set at 0.2 mm and specimens were printed with three different raster directions: 0 ° , 45 ° and 90 ° . Fig. 1 show schematics of intact and defected specimens with different raster angles. Based on the raster orientation, 0 ° and 90 ° , orientation denoted that the rasters are along and transverse to the loading direction, respectively. Since in the fabrication of 3D-printed parts, manufacturing defects can occur, here we have considered gaps (missing extrudates) as a manufacturing defect. Therefore, in the defected specimens a certain gaps were intentionally placed into the test coupons. The effects of this gap on the structural integrity of the parts were determined by comparing behavior of intact and defects specimens.

Fig. 1. Schematics of 3D-printed specimens with different raster directions (intact and defected test coupons, dimensions in mm)

Since printing process parameters affect the structural performance of the parts, in this study, printing parameters such as layer thickness, feed rate, and fill density were kept constant in printing of all test coupons. Indeed, among the design and printing parameters, only raster orientation and inclusion of defects were changed in the specimens. In the defected specimens, the missing extrudates were oriented with the raster directions. It is noteworthy that in the fabrication of the specimens with above-mentioned raster angles, different number of extudates were not printed to keep the same defects area percentage in all defected specimens.