PSI - Issue 72

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

493

mechanical and structural changes of PLA specimens produced with FDM and DLP-LCD technologies over an aging period of two months. Standardized three-point bending tests and microscopic analyzes will be used to find out how 3D-printed PLA components degrade over time and which factors influence their durability. By examining the aging process in more detail, this research should provide valuable insights into the long-term performance of components and refine material selection and printing techniques to create stronger, more resilient parts. 2. Methodology Three point bending test specimens made from PLA filament and PLA-like resin were fabricated in accordance with ISO 178:2019 standard (see Fig. 1). For each additive manufacturing (AM) technique fifteen specimens in three batches (five specimens per batch) were produced to ensure consistent and reliable results. First batch were dedicated for immediately testing, second batch for testing after period of one month and third batch for period of two months. The FDM specimens were printed using a Creality CR-10 Smart Pro (Shenzhen, China), while the resin specimens were manufactured using two different systems: a desktop digital light processing (DLP-LCD) printer (Creality LD 002R, Shenzhen, China).

Fig. 1. Specimen geometry according to the ISO 178:2019 standard for three point bending test (dimensions in mm).

To maintain comparability across the different methods, all specimens were printed with identical settings: 100% infill density, grid-style infill pattern, and raster orientation fixed at 90°. Three point bending tests were conducted under controlled laboratory conditions, specifically at a room temperature of approximately 23°C and relative humidity maintained at 55%. The mechanical tests were carried out using a Shimadzu AGS-X universal testing machine (Shimadzu Corporation, Kyoto, Japan) equipped with a 100 kN load cell. The test procedure complied with the ISO 178:2019 standard, with the crosshead displacement rate set at 2 mm/min. A three-point bending configuration was applied to a total of thirty specimens, equally divided into two fabrication groups: fifteen specimens were fabricated by FDM and fifteen DLP LCD. Within each fabrication group, specimens were divided into three aging intervals (n = 5 per group):  0m group: tested immediately after fabrication,  1m group: tested after one month of ambient aging,  2m group: tested after two months of environmental aging. All mechanical tests were carried out under identical environmental and load conditions. The raw force displacement data collected from the testing machine was processed using MATLAB R2022b software (MathWorks, Natick, MA, USA) to derive average engineering stress – strain curves for each of the six batches of specimens. Over a period of two months, the specimens were left to age naturally under everyday indoor conditions. They were washed daily, not as part of a formal protocol, but to simulate how materials might behave if used in real-life scenarios where they’re exposed to routine hygiene and environmental factors while not actively in use. As part of the routine, each specimen was washed once a day with warm water (about 37°C) using Frosch gel.