PSI - Issue 72

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

492

Keywords: additive manufacturing; 3D printing; fused deposition modeling (FDM); digital light processing (DLP); PLA filament; PLA-like resin; three points bending; microscopy; aging

1. Introduction With advances in additive manufacturing (AM), it is no longer limited to prototyping, but has become an essential tool for the production of functional components in critical industries, Ngo et al. (2018), Gross et al. (2014). Imp rovements in material selection, precision and surface quality have accelerated the adoption of this technology. However, the long-term stability of printed materials under different environmental conditions is still an area under investigation, Gebisa and Lemu (2018), Rankouhi et al. (2014).

Nomenclature AM additive manufacturing FDM fused deposition modelling DLP digital light processing LCD liquid-crystal display PLA polylactic acid

While AM offers significant advantages, particularly with thermoplastic materials, such as polylactic acid (PLA), ensuring durability, reliability and structural integrity over time is a key scientific challenge, Tymrak et al. (2015), Chacón et al. (2017). Fused deposition modeling (FDM) and digital light processing (DLP-LCD) have emerged as two of the most widely used manufacturing methods, especially for cost-sensitive and custom applications. Both processes offer significant advantages in terms of mechanical properties, surface finish and suitability for different environments Travieso-Rdoriguez et al. (2019), Rajan et al. (2022), Swetha et al. (2024). FDM is based on the application of thermoplastic filaments, while DLP selectively cures liquid resin by LCD projection. Comparing their resistance to environmental stresses is crucial for optimizing material selection. Evaluating mechanical performance is key to understanding the reliability of 3D printed components. The three point bending test is commonly used to evaluate flexural strength and stiffness and is therefore particularly important for investigating the durability of PLA-based FDM prints and resin-based DLP prints, Tóth  2024). These materials react differently to mechanical stress and environmental aging, which has a direct impact on their suitability for long term applications. Aging effects in polymer-based 3D printed materials raise concerns about longevity, especially in applications that require longer performance stability. Over time, the mechanical properties of PLA degrade due to environmental influences, reducing tensile strength, elasticity and structural integrity Domerg et al. (2024). To address these concerns, a deeper understanding of PLA’s aging behavior is needed to improve material formula tions and printing techniques. Several strategies can improve the durability of PLA in real-world applications. Design modifications, such as reinforcing stress-prone areas with thicker sections and ensuring uniform stress distribution, improve longevity without significantly increasing costs, Hedayati et al. (2024). Studies indicate that PLA is significantly altered by environmental influences, Golubovi ć et al. (2024). Interestingly, aged PLA specimens exhibited 8.8% higher maximum force capacity compared to fresh specimens, but strain analysis showed reduced flexibility over time, indicating a trade-off between strength retention and brittleness of the material, Mitrovi ć et al. (2024) . This discussion is particularly important as 3D printing is increasingly moving into areas that require long-term performance, such as personalized medical devices, structural components in agriculture and filtration systems in environmental engineering, where both dimensional stability and mechanical stability are critical, Alzoubi et al. (2023), Saheb (2024). With the increasing use of 3D-printed PLA components in various applications, it is important to understand how aging affects their mechanical and structural integrity. This knowledge is crucial for predicting their lifespan and ensuring the safety and efficacy of PLA-based products. Therefore, the aim of this study is to investigate the