PSI - Issue 56

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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and rectangular shape for two traces and fourteen traces. The dimensions considered for determining the sections are presented in the figure 5. The resulted sections were used in computing the tensile stresses. Differential Scanning Calorimetry analysis were performed using DSC 204 F1 Phoenix equipment (Netzsch) on two types of samples: raw filament and extruded filament. Curves were recorded under nitrogen to prevent moisture and oxidative degradation and under dynamic conditions from room temperature to 300°C with 10 K/min heating rate. The samples (around 5 mg) were placed in closed aluminum crucibles (average mass 39±0.2 mg). Data were analyzed using Proteus Analysis 6.1.0 software.

Fig. 4. Filament test stand and machine.

Fig. 5. Characteristic dimensions of the considered cross sections

3. Results and discussions The analysis of the tensile tests results followed a chain approach. In the figure 6 are presented all stress-strain curves according to the sample types. All curve follows the same trend until a maximum stress is recorded, followed by a drop in the curve to a stabilization level, where the stress remains constant and the material elongates until breaking. The behavior of the for raw filament and air extruded filament are similar in terms of tensile strength and elongation at break, meaning that the internal structure of the polymer remains similar after thermal reprocessing. The fine details in property difference will be further explained by DSC analysis. In the case of fourteen traces samples, only the elongation at breaks shows a reduction compared to the air-printed filament. This can be put on slower cooling rate to solidification due to the heated platform. The cooling rate is directly influencing the crystallinity of the polymer, slow cooling leading to high crystallinity and therefore smaller elongation at break. In addition, the adhesion between the filaments helps in maintaining a high tensile strength.