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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machines are desktop versions, unlike the industry-grade SLA machine used here. Another research output here is the comparison of the industrial-grade machine with desktop ones. Printing properties were set to be as similar as possible hence, specimens were fabricated with 100% infill density, with a grid infill pattern, and with a 90° orientation of rasters. All tensile tests had the same conditions, i.e., they were tested at room temperature (around 23 ℃ ) and relative humidity of 55%.

Fig. 1. Specimen geometry according to the ISO 527-2 standard (dimensions in mm)..

Tensile tests were performed on the Shimadzu AGS-X machine (Shimadzu Corp., Kyoto, Japan) equipped with a load cell of 100 kN capacity. The testing speed was set to 1 mm/min. Optical 2D and 3D microscopy were utilized after conducting tensile tests, on laboratory-grade 3D Digital Video Microscope KH-7700 (Hirox, Tokyo, Japan). 3. Results and Discussion ABS material represents the toughened modification of styrene-acrylonitrile (SAN) copolymer, where toughening is achieved by adding the sub-microscopically small rubber particles in the coherent brittle SAN matrix (Grellmann et al., 2001). The amount and manner of dispersion of those particles have a direct influence on the morphology and materials’ mechanical properties. It is already well -known that ABS resins share time-dependent behavior, i.e., their mechanical properties are influenced by the straining rate, as well as by the volume of rubber content (Bernal et al., 1995). All tested specimens, from both of the stated materials, exhibited brittle fracture behavior (see Fig. 2, upper level). Further 2D and 3D optical microscopy analysis was conducted for topography and morphology observation. Taken images showed different textures, depending on applied printing regimes (see Fig.2, Middle and Lower level). One of the purposes of the utilization of optical microscopy is to find any defects, which would be proof of irregularities and abruptions in specimens’ integrity. On the FDM fracture surface, there is a considerable size difference in the present internal gaps, located between printed raster lines. Such a gap size inconsistency refers to uneven intra- and inter-layer bonding in the structure. This anisotropy of FDM specimens is shown in the leftmost 2D image in Fig. 2, Middle level. Naturally, when the surrounding gaps are bigger in size, the raster lines are more visible. The other two 2D images in Fig. 2, Middle level, show expected similarities in fracture surface structure on both Vat photopolymerization AM technologies. As one can see in all 2D images from Fig. 2- Middle level, there is a major difference in resolution and accuracy of both Vat photopolymerization AM technologies in contrast to FDM one. Fig. 2- Lower level is dedicated to 3D images: here, in the leftmost image one can see the two-level fracture surface on FDM sp ecimens. FDM specimen’s 3D image gives a better insight into the fracture morphology where one can clearly see two predominately flat surfaces, separated by a ridge. This particular ridge reveals the location of probable low inter-layer bonding, which caused the separation between layers. From the 3D image, it is visible that the highest deformation is present at the ridge peak. Namely, after the inter-layer separation the closest layers receive higher loads. Hence, the highest level of ductile deformation is cited all along the ridge edge.