PSI - Issue 72

Božica Bojović et al. / Procedia Structural Integrity 72 (2025) 491–498

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3. Results and Discussions 3.1. Flexural testing results

To ensure consistency and comparability, each average stress – strain curve represents the mean of the five specimens within a group, limited to the strain interval prior to the first specimen failure. Data beyond this point were excluded due to incomplete data availability for the entire specimen set. This approach is consistent with the methodology developed in our previous work [13]. Fig. 3 illustrates the different mechanical response of PLA specimens produced by FDM and DLP-LCD, which can be attributed to the differences in polymer chemistry. The PLA filament used in FDM printing has higher elasticity, while the photo-cured PLA-like resin in the DLP-LCD process has greater flexibility. These inherent material differences result in different bending behavior, with the specimens printed with FDM having a higher bending strength than those produced with DLP-LCD. The effect of aging over a period of two months is shown in Fig. 2, with FDM specimens in Fig. 2a and DLP-LCD specimens in Fig. 2b. For the FDM group, the average stress – strain curves show a strong overlap in the elastic range up to the yield point, independent of the aging period. After the yield point, all FDM specimens show comparable behavior after the yield point, although a decrease in ductility can be observed with increasing aging time. It is noteworthy that the flexural strength values remain relatively constant across all FDM aging groups. In contrast, the DLP-LCD specimens show progressive changes in mechanical behavior with increasing aging. The average curves show a clear variation in elastic slope and flexural strength between the aging intervals. A reduction in flexural modulus and flexural strength can be seen after only one month, with a more pronounced deterioration observed after two months. Interestingly, despite the mechanical deterioration, the DLP-LCD specimens exhibited prolonged deformation after stretching, indicating enhanced apparent ductility with aging.

a) b) Fig.2. Stress-strain curves for aging specimens made by a) FDM and b) DLP-LCD technology.

In this research, a comparative analysis of the three most important bending parameters was carried out: Flexural modulus, flexural strength and flexural strain at break. The mean values and the corresponding ranges for each parameter in all test groups are summarized and plotted in Fig. 3. In the test specimens produced from PLA filaments using FDM, the flexural modulus showed negligible variation over the observation period, indicating that elastic stiffness was maintained. The flexural strength decreased only slightly, while the flexural strain at break increased slightly. These results indicate that the PLA specimens printed with FDM maintained their flexural elasticity, with a marginal tendency towards increased ductility.