PSI - Issue 56

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Dan Ioan Stoia et al. / Procedia Structural Integrity 56 (2024) 90–96 Author name / Structural Integrity Procedia 00 (2019) 000–000

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2. Material and methods The investigated material is a yellow color polylactic acid (PLA) filament with a diameter of 1.75 mm. The PLA filament is a semi-crystalline and recyclable thermoplastic polyester that is derived from renewable resources such corn starch or sugar cane. The filament is biodegradable with high heat capacity and good mechanical strength. The analysis carried out in the paper is based on tensile tests on the following types of samples: raw filament; air extruded filament, one trace deposited on the platform, two consecutive traces deposited on the platform and fourteen consecutive traces deposited on the platform (figure 2). The printing was done on a Makerbot Sketch 3D printer, keeping the printing parameters constant: build plate temperature + 50°C; extruder temperature + 220 °C; extruder print speed – 35 mm/s. In order for the filament to be easily removed from the platform’s surface, the platform was covered with adhesive tape. The deposition consists only in 1 layer. After printing the samples were subjected to microscopical examination in order to identify defects in adhesion between traces, in the purpose of removing those samples from the mechanical testing. In the figure 3 it can be observed at 5:1 scale, the image of the raw filament and the sample that consist in fourteen deposited traces.

Fig. 2. Air extruded and filament deposition on the platform.

Fig. 3. Microscopic images of (a) raw filament and (b) 14 printing traces, 40X.

The filaments were tested on a Metrotec universal testing machine (figure 4), with a load rate of 2 mm/min. Two load cells of 50 N and 1000 N respectively, same accuracy, were used. The cross-sections of the original and air printed filaments are circular, with diameters of Φ 1 = 1.75 mm and Φ 2 = 0.5 mm, respectively. The cross-sections of the deposited traces were microscopically measured and approximated to an elliptical shape for one deposition trace,