PSI - Issue 42

Valerii Matveenko et al. / Procedia Structural Integrity 42 (2022) 307–314 V.Matveenko, N.Kosheleva, G.Serovaev/ Structural Integrity Procedia 00 (2022) 000 – 000

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industries, such as energy (Mofidian and Bardaweel, 2019), medicine (Suresh Kumar and Krishnamoorthi, 2021), automotive (Lee, An and Chua, 2017) and aerospace (Liu et al. , 2017). One of the most popular methods is the material extrusion method, also known as the fused deposition modeling (FDM) (Kousiatza and Karalekas, 2016), in which material is sequentially extruded through a heated nozzle onto a platform forming layers until the required part is obtained. Filaments made from thermoplastics which gradually soften and melt under the influence of temperature are used in FDM printing. On the platform, the melted material quickly cools and hardens. One of the disadvantages of FDM method is the accumulation of internal residual stresses and strains during layer printing process. Rapid transitions from one physical state to another (repeated melting and rapid cooling cycles) lead to generation of non-uniform stress and strain distributions in the sample. The latter can affect the size accuracy of the sample and lead to delamination and cracking of the material. Information about the temperature distribution inside the 3D printed sample plays an important role in determining the quality of the interlayer bonds and the final mechanical properties of the structure. The application of fiber-optic sensors (FOS) is one of the promising solutions for structural health monitoring of 3D printed products. FOSs can be embedded in such products during their fabrication and can provide data on the mechanical conditions of the structure throughout its entire service life. In (Kousiatza and Karalekas, 2016) it is shown that embedded FOSs based on fiber Bragg gratings (FBG) can be used for continuous real time monitoring of strain fields. Also a methodology that allows simultaneous monitoring of strain and temperature distribution by the optical spectrum of an embedded FOS during the entire FDM process is presented. It is shown that the strain levels are strongly influenced by the resulting temperature gradients. The data demonstrates that the embedded FOS system has proven to be a reliable choice for real-time monitoring of the FDM process and the quality of the printed samples. In (Chen et al. , 2021) the residual stresses of printed lamellae produced by the FDM method are investigated. It has been shown that during lamella fabrication, a high temperature gradient can lead to dangerous residual stresses, which in turn leads to material delamination. To improve the quality of manufactured 3D parts, a theoretical model was developed that, together with the experimental data obtained from the FBG-based FOS, allows to determine the residual stresses in the printed lamellae. It is shown how the printing parameters (layer thickness, printing direction, etc.) influence the residual stresses. Paper (Reggiani Manzo et al. , 2019) is devoted to the numerical and experimental study of monitoring the mechanical state of 3D-printed cases using embedded FBG based sensors. The authors made recommendations according to the positioning of the optical fiber and the adhesion between the case and the printer bed surface. It is worth noting that the combined use of FOS and additive technologies solves the problems associated with the protection of fiber-optic sensors (Matveenko, Kosheleva and Serovaev, 2022). In (Hong et al. , 2019) it is shown that special encapsulation of the FBG sensor in polylactide (PLA) can effectively eliminate the disadvantages associated with optical signal loss and the complicated process of subsequent sensor embedding. In (Yang et al. , 2019) the circumferential strain gauge based on FBG fabricated using the FDM method was shown. Test results show that the new FBG-based circumferential strain gauge can effectively control circumferential displacement and vertical cylinder pressure. Paper (Yan et al. , 2020) is also devoted to the technology of FBG-based FOS packaging using additive technologies. The paper analyzes the effect of the characteristics of the packaging material on the FBG, especially the temperature. The stability of a FBG sensor encapsulated in PLA was experimentally investigated. It is shown that such a 3D-printed packaging structure can not only effectively protect the FBG, but also sensor with high stability can be obtained. In this paper the most common variant of additive technology - FDM was considered. Any common thermoplastic material used in the manufacture of objects by this technology can be applied, as their melting temperature does not exceed the temperature limits for optical fibers. Such materials include polylactide (PLA), polyethylene terephthalate-glycol (PET-G), acrylonitrile butadiene styrene (ABS), high impact polystyrene (HIPS) and others, as well as composites with carbon, fiberglass, aramid and other fillers based on these plastics. This paper presents the results of measuring the technological strains and temperatures occurring in the material during the 3D printing process using embedded point FOSs based on FBG and distributed FOS (DFOS) based on Rayleigh scattering.