PSI - Issue 25

S. Valvez et al. / Procedia Structural Integrity 25 (2020) 394–399 S.Valvez et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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Heidari-Rarani et al. (2019) designed and manufactured an extruder for fused deposition modelling 3D printers to produce continuous fibre reinforced thermoplastic composites. In this device, continuous fibres and melted plastic are combined with each other in the extruder and deposed in a simultaneously manner. To assess the quality of the samples, tensile and three-point bending tests were performed using pure poly lactic acid (PLA) samples and specimens of continuous carbon fibre reinforced PLA composites. Both materials (PLA and composite) were printed along the longitudinal direction to reach their highest strength. Comparatively to the PLA samples, tensile modulus and ultimate tensile strength increased around 208% and 36%, respectively, while the failure strain decreased about 62% when the continuous carbon fibres were added. Regarding the bending modulus and maximum bending strength the improvements were about 367% and 109%, respectively. Finally, the damage mechanisms of carbon fibre reinforced PLA composites under bending loads were observed, and the dominant failure modes were delamination and delamination-induced-matrix cracking. The first micro-cracks occurred between layers, which propagate along the specimen length and cause delamination between the two layers. When the interlaminar cracks reach each other, they create vertical cracks in the layer just below the loading nose and, simultaneously, underneath the neutral axis. Finally, both types of the cracks from two sides propagate toward each other and cause final failure. Chaudhry et al. (2019) developed a new solution, in which a 1 mm hole was drilled on the side of one of the faces of the nozzle at 45º. The angle was selected to facilitate the flow of fibre into the melted filament and, during the printing process, does not flow-out by the hole. Furthermore, carbon fibre is also fed in a hot zone for easier printing. Several parameters were analysed, including thread count and interlayer gap, and after optimization tensile strength around 112 MPa and flexural strength around 164 MPa were obtained for continuous carbon fibre reinforced PLA composites. These values are almost 3 times higher compared to neat PLA. Therefore, it was possible to conclude from the results obtained that the adopted solution is efficient. Compared to other studies, the results obtained with this equipment for both materials are promising, regardless of many processing parameters may differ from those used. Considering the industrial competitiveness, better management of available raw materials, environmental concerns and the ability to develop more complex products, additive manufacturing (AM) techniques have proved to be the most promising in recent years. In fact, the attractive combination that AM offers on the composite materials field is a unique opportunity for companies, researchers and consumers to explore. From all additive manufacturing techniques, the most widely used is FDM (Fused Deposition Modelling). On the other hand, because polymers do not have adequate mechanical performance for structural applications, fillers are required to improve their mechanical properties. It is possible to conclude that continuous carbon fibers are a good option for improving the mechanical properties of PLA composites and, in this context, a possible solution for structural applications. However, literature does not present many studies on the subject, but the available ones report some difficulties on the production of such composites due to limitations still observed in the available 3D printers. On the other hand, the mechanical properties are greatly influenced by various parameters like: workpiece depositing parameters, FDM machine setting-up parameters, environmental factors, material properties, etc. Nevertheless, the raster angle, infill speed, nozzle temperature and layer thickness are selected as the major FDM process parameters, which are not yet conveniently optimized to maximize the mechanical properties. Therefore, further studies are needed to develop this technology to be applicable on future industrial applications. 4. Conclusion

Acknowledgements

This work was supported by the project Centro-01-0145-FEDER-000017-EMaDeS-Energy, Materials and Sustainable Development, co-financed by the Portugal 2020 Program (PT 2020), within the Regional Operational program of the Center (CENTRO 2020) and the European Union through the European Regional Development Fund (ERDF) and by the project SAICT nº 31296 “COMP4UAV s ” supported by POCI in its FEDER component and by FCT-IP.