PSI - Issue 72

Miloš Vorkapić et al. / Procedia Structural Integrity 72 (2025) 470 – 478

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Potential mechanisms of such fracture behavior at the microstructural level could be explained by stronger interlayer adhesion in the XY plane, which contributes to better stress transfer and crack bridging, improving impact resistance. Less interlayer weakness in XY samples compared to XZ and YZ means that cracks propagate through the material rather than along weaker layer boundaries. Also, the higher temperature promotes energy dissipation as the polymer chains gain mobility, allowing better plastic deformation instead of brittle fracture. The combined effect of enhanced polymer ductility and fiber reinforcement at elevated temperatures explains why the XY-oriented PLA/CF samples performed best under these conditions. These findings align with previous research, highlighting the influence of fiber orientation, interlayer adhesion, and temperature-dependent ductility on impact resistance. The XY orientation demonstrated superior impact resistance due more efficient stress transfer, allowing the composite to absorb and dissipate impact energy effectively. Lower impact toughness of the samples printed in the XZ and YZ orientations, attributed to weaker interlayer bonding and delamination effects, was previously reported by Tymrak et al. (2014). The observed anisotropic mechanical behavior, where XY orientation consistently outperforms other printing directions in terms of impact resistance was also reported by Jamadar et al.(2024). The significant improvement in impact toughness at higher temperatures was explained by Wang et al. (2021), according whom PLA undergoes a transition from brittle to ductile behavior near its glass transition temperature (Tg), typically between 55 – 65°C, meaning it can deform more before breaking, leading to greater energy absorption in the Charpy test. Below T g the PLA behaves as a rigid, brittle polymer, leading to sudden fracture upon impact, Ahmed et al. (2021). The results suggest that PLA/CF composites are highly suitable for applications requiring lightweight materials with high impact resistance, especially when printed in the XY orientation and used at elevated temperatures. This is particularly relevant for structural components in drones, automotive parts, and aerospace applications, where weight reduction and mechanical durability are critical design factors. Future research should focus on optimizing its mechanical properties through modifications in fiber content and processing conditions. 4. Conclusions Additively manufactured PLA/CF composites were prepared and examined in form of specimens for tensile and impact testing, as well as for DSC analysis. It has been confirmed that printing orientation and temperature significantly affect the material’s properties. DSC revealed increased c ritallinity of PLA/CF compared to PLA. The highest tensile strength is observed in the XY orientation at room temperature, reaching ~40 MPa. The highest strain values occur at higher temperatures, indicating increased ductility. Regarding the values of elastic modulus, at - 30°C the material is stiffer (higher modulus), while at +50°C it becomes much more compliant (lower modulus). A dramatic reduction in tensile strength and stiffness is observed at +50°C for all printing orientations. PLA/CF exhibits the highest impact toughness in XY orientation of 3D printing, and the best results were obtained for XY samples at higher temperatures. Additively manufactured PLA/CF composites are a promising material for applications in industries that require high mechanical performance and thermal resistance. Solid parts produced by this technology are necessary nowadays for installation in places under substantial mechanical loads and require good heat resistance. The observed mechanical characteristics of the additively manufactured material provide good starting point for its potential use in the production of spare parts for automotive, nautical, sports industry as well as in lightweight aircrafts constructions and various protective materials. Future work on the studied material would encompass investigation of long-term durability and fatigue resistance, as well as optimization of printing parameters to further improve performance. Acknowledgements This research has been financially supported by the Republic of Serbia, Ministry of Science, Technological Development and Innovation (grants no. 451-03-136/2025-03/200026, 451-03-136/2025-03/ 200105, 451-03 137/2025-03/200325 and 451-03-136/2025-03/ 200012). We especially acknowledge support through the UNDP circular voucher number 00131890/00145003/2023/01-12 and Flexisense d.o.o, Belgrade, Serbia.