PSI - Issue 79

Charoula Kousiatza et al. / Procedia Structural Integrity 79 (2026) 146–154

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residual strains detected in the bottom layers of the FDM-fabricated composites. Finally, it is important to note that the ultimate strength and Young’s modulus values, calculated in the current study for the FDM-built CF-PA composites, are in good agreement with values reported in literature for FDM-printed composites with the same or similar fiber reinforcement content. More specifically, Muhamedagic et al. reported tensile modulus and ultimate strength values of 7.625 GPa and 110 MPa, respectively, for FDM-built composites made from the same short CF PA filament used in the current research work (Muhamedagic et al. 2022). Additionally, Li et al. studied the mechanical properties of FDM-manufactured short CF-PA composites with respect to their fiber content. The composite specimens containing 14.6 wt% CF, designated as PA6-15CF, which is close to the fiber content of the composite samples investigated in this work, exhibited a Young’s modulus of about 5.8 GPa (Li et al. 2022). 4.4. SEM analysis The SEM image of a dogbone specimen after fracture with the integrated FBG is indicatively presented in Fig. 5. It is observed that the optical fiber exhibited sufficient interfacial bonding with the host composite material over the majority of its perimeter with only minor peripheral gaps detected around the FBG sensor. It is noted that the evaluation of the FBG sensors’ embedment quality through the structures’ thickness was not feasible, as significant deformation of the optical fibers was observed on most of the test coupons’ fractured surfaces.

Fig. 5. Quality of the FBG sensors’ embedment within the 3D printed host composite material based on SEM analysis.

5. Conclusions The FDM method is one of the most popular and promising AM techniques. Furthermore, FBG sensors present many advantages due to their small size, light weight and high sensitivity. In the current study, the suitability of FBG sensors for the mechanical characterization through the thickness of FDM-built composites was examined. More specifically, optical sensors were embedded through the thickness of 3D printed specimens made from chopped carbon fiber-reinforced polyamide (CF-PA) composite during the printing process. All the specimens, after their fabrication, were subjected to tensile loading. The stress-strain curves and the Young’s modulus, as calculated from the optical sensors’ recordings, were compared to those derived from the extensometer recordings. The experimental results are in good agreement, showing that the FBG sensors can be used for the calculation of the Young’s modulus of FDM fabricated composites and, in general, for FDM structures’ mechanical characterization. Acknowledgements This work has been supported by the National Program “Research-Create-Innovate B Round”, Operational Program Competitiveness, Entrepreneurship and Innovation 2014-2020 (EPAnEK), General Secretariat of Research and Innovation, Hellenic Republic and within the context of the “OrThOP3Dics/TAEDK-06191” research project.