PSI - Issue 49

Federico Fazzini et al. / Procedia Structural Integrity 49 (2023) 59–66 / Structural Integrity Procedia 00 (2023) 000 – 000

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The other main printing parameters were held constant throughout the experiments. The layer thickness was maintained at 0.20 mm, the nozzle diameter was 0.4 mm, and the infill density was fixed at 100%. The bed temperature was kept at 110°C, and an adhesive was applied to enhance the adhesion of the first layer and minimise warping. The build orientation of the specimens was horizontal with respect to the build platform. To configure the orientation of the test samples, adjust additional process parameters, and generate the slicing instructions, the free software Ideamaker was chosen after conducting preliminary trials with two other slicing software packages. To analyse the mechanical and dimensional properties for each of the 12 parameter combinations, three tensile specimens, three compression specimens, and two cubes of different sizes were printed per combination, resulting in a total of 96 produced specimens. The analysed outputs for each sample type were the ultimate tensile strength, Young's modulus, yield stress, elongation at break respectively under tension and compression plus porosity and microstructure. 2.3. Specimen geometries and dimensions There is a notable lack of material testing standards specifically tailored for metal FFF components, as well as a scarcity of guidance on preparing appropriate test specimens with mesostructures that accurately represent the final part under analysis, Phillips et al. (2022). The geometry and dimensions of the tensile specimens were selected following the ASTM E8 standard (2022) for Powder Metallurgy (P/M) Products, with a thickness of 4 mm. On the other hand, the compression specimen does not comply with any specific standard. They show a quare cross section prism shape with dimensions of 8x8x15 mm. Two cube samples per manufacturing conditions were also produced for metallographic and porosity investigation. The two cubes sample have side lengths of 10 mm and 5 mm, respectively. Figure 1(a) depicts the tensile specimen B, while figure 1(b) illustrates two compression specimens A. 2.4. Experimental campaign Each of the 96 specimens underwent size measurement using a Neoteck digital micrometre with a sensitivity of ±0.01 mm and an accuracy of ±0.1 mm. Additionally, a Mitutoyo digital calliper with a sensitivity of ±0.01 mm and an accuracy of ±0.1 mm was employed for the measurements. Any measurement was repeated three times for statistical basis. The tensile and compression tests were conducted using an Instron 8516 universal testing machine equipped with a 100 kN load cell. A dynamic extensometer, specifically the Instron 260-601 model, was used during the tensile tests. The testing speed was set at 1 mm/min. Compression tests did not employ the extensometer and were performed at a crosshead speed of 1 mm/min. Prior to conducting the tests, the identifying letters corresponding to each combination were smoothed by filing them off from both the tensile and compression specimens. For the compression specimens, the faces that would come into contact with the machine platens were grinded to made them parallel. The tests were repeated three times per conditions. 3. Results and discussion A total of 36 traction tests were performed till separation failure to gather data on displacement from the extensometer and load measurements from the load cell. These data, combined with the knowledge of the specimen geometry, allowed for the determination of various mechanical properties, including engineering ultimate tensile stress (UTS), engineering yield stress (Rp0.2), Young's modulus (E), and elongation at fracture for each specimen. While a b Fig. 1. (a) tensile specimen 112-B; (b) compression specimens 111-A.