PSI - Issue 56

Zorana Golubovic et al. / Procedia Structural Integrity 56 (2024) 153–159 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 2. Upper - Images of ISO 527-2 fractured specimens: a) FDM; b) SLA; c) DLP; Middle - 2D micrographs: d) FDM; e) SLA; f) DLP; Bottom - 3D micrograph: g) FDM; h) SLA; i) DLP (Golubović et al., 2023) .

Unlike FDM, the fracture surfaces in SLA and DLP specimens are principally flat. In Fig. 2 (Middle level), the second 2D image is dedicated to SLA: here, the fracture surface is flat except for the left side where the polymer material was pulled upward for 200 μm. A bett er visualization of the stated can be seen on the 3D image of the SLA fracture surface, placed one image below (see Fig. 2, Lower level). Due to different refraction from the fracture surface in the 2D image, one can assume that the ductile fracture is present on most of the specimen, except for the pulled small portion of the material, where it experienced a brittle fracture. Images dedicated to DLP specimens are placed on the right-hand side in Fig. 2. The brittle fracture is present on the whole fracture surface, see 2D image (Fig. 2, Middle level). Apart from the nature of the fracture, one can also see the bubbles scattered all over the fracture surface. The irregularities in shape and size of the bubbles are better visualized in the 3D image (Fig. 2, Lower level). From the 2D image, it is also noticeable that the outer surface has a different appearance from the interior: namely, due to the post-curing of the specimens via LED lamps it is apparent that the outer surface is better polymerized that the sp ecimen’s inside. The size of the bubbles is in order of 240 microns (see 3D image). The origin of bubbles is from the shaking of the resin in the bottle, right before pouring the liquid into the vat. Due to the lower energy of the UV light source in DLP, not all the bubbles disappeared during the AM process, i.e., some got trapped inside the cured resin. Fig. 3 represents the engineering stress-strain interpretation of all the tensile results. In order to show the repeatability of the results, the three diagrams are meant to show all the curves from tested batches. Here, one can see