PSI - Issue 72

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

495

Flexural Modulus MPa

Flexural Strength MPa

Flexural Strain at Break %

2m

2m

2m

1m

1m

1m

0m

0m

0m

0 1000 2000 3000 4000

0

50

100

0

10

20

0m 1m 2m DLP 1637,13 1345,06 737,863 FDM 3563,23 3650,62 3603,72

0m 1m 2m DLP 66,288 49,623 28,984 FDM 97,319 93,446 91,398

0m 1m 2m DLP 6,725 9,267 9,701 FDM 9,755 10,192 11,399

a) c) Fig. 3. Flexural properties for aged specimens made by FDM and DLP-LCD technology: a) Flexural modulus, b) Flexural strength and c) Flexural strain at break. In contrast, specimens produced using DLP-LCD from PLA-like resin showed a significant reduction in flexural modulus and flexural strength, as well as a slight increase in flexural strain. These changes indicate a clear shift in the mechanical behavior of the resin-based specimens towards increased flexibility during the observation period. Quantitatively, the effects of two months of aging and immersion (bathing) are as follows. For FDM (PLA) specimens: b)

 Flexural modulus increased by less than 2%,  Flexural strength decreased by up to 9%,  Flexural strain at failure increased by up to 17%. For DLP-LCD (PLA-like resin) specimens:

 Flexural modulus decreased to approximately 45% of its initial value,  Flexural strength decreased to approximately 43% of its initial value,  Flexural strain at failure increased by up to 17%.

In summary, the PLA specimens printed with FDM exhibited stable mechanical properties over a two-month period, characteristic of a stiff and tough material that remained intact under normal flexural deformation. In contrast, DLP-LCD printed specimens showed a marked deterioration in flexural stiffness and strength, combined with an increase in flexibility. This indicates a transition of the material to a more ductile behavior at the expense of structural stiffness. 3.2. Microscopy results Digital optical microscopy was used to further investigate the surface topography and fracture morphology of the tested specimens, using magnifications from 50× to 100×. This analysis provided additional insight into the microstructural features related to material behavior during and after mechanical loading. It is important to note the fundamental difference between the manufacturing technologies and the materials: DLP LCD printing produces a nearly isotropic structure using a photopolymer resin that cures layer by layer through UV exposure, while FDM printing extrudes thermoplastic filaments, resulting in an inherently anisotropic structure with visible interlayer boundaries.