PSI - Issue 53
P.N.B. Reis et al. / Procedia Structural Integrity 53 (2024) 309–314 P.N.B. Reis / Structural Integrity Procedia 00 (2019) 000–000
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its enormous advantages over conventional manufacturing processes. It makes it possible to produce components with high complexity in terms of shape and internal geometric details, freedom of design, use of various materials, less waste, low costs, and reduced manufacturing times. The procedure followed to obtain parts produced by FFF consists of creating a 3D model of the desired part in CAD software, then dividing the part into several planes where each one will have a path to follow, and finally, a numerical command that will be read by the printer and from which the component is printed (Ziemian et al., 2012). In general, the mechanical properties of polymer components manufactured using this technique are lower than those obtained using traditional processes (Gao et al., 2019), but optimizing the manufacturing parameters makes it possible to obtain similar or even superior properties (Behalek et al., 2018). In fact, the mechanical performance of these components depends mainly on intra-filament strength, i.e., the mechanical properties of the extruded material (the main factor when the direction of the load is the same as the direction of the filaments), but also on inter-filament strength, which depends on the adhesion between layers and the shear strength at the bonding interface (Spoerk et al., 2017). In engineering and structural applications, strength, stiffness, and dimensional stability are usually the main attributes that must be taken into account. The study of the materials manufactured by this technique is very important because they have enormous viscoelasticity, which must be analysed, especially to understand their response in long term applications. In this context, elastic properties, Young's modulus, and stiffness variation must receive special attention when improving a composite material (Vilaseca et al., 2018). On the other hand, a good knowledge of the modulus of elasticity and the evolution of stiffness is decisive for analysing the mechanical behaviour of the composite (Reis et al., 2011). Therefore, this study aims to analyse the mechanical response of composites reinforced by short carbon fibres and graphene subjected to defined load histories in order to understand the mechanical behaviour of the material. 2. Material and Experimental Procedure The material used to manufacture the specimens is known commercially as G6-Impact™, produced by Graphene 3D Labs. It is a HIPS (high-impact resistant polystyrene) polymer matrix composite reinforced with graphene and short carbon fibres and was supplied in form of a 1.75 mm diameter filament. HIPS is the result of adding rubber to the polystyrene polymer, which, as the name suggests, makes it much more resistant to impact. The supplier does not correctly explain the relative amount of carbon fibres and graphene in the matrix, stating only that the percentage of both is 20 wt.%. The specimens used in this study were produced on a CreatBot F430 3D Printer, with the geometry shown in Figure 1. The lay-up used was concentric, in which the deposition of the filament inside the specimen is always parallel to the contour. This ensures that in the central area of the specimen, all the filaments are deposited in the same loading direction and that the discontinuities inherent to the manufacturing process are found in the center of the specimen and not and not in the contour transition zone. The printing parameters used in this study were: nozzle temperature of 235 ºC; bed temperature of 85 ºC; printing speed of 10 mm/s; layer height of 0.25 mm; and infill 100%.
Fig. 1. Geometry and size of the specimens used in this study (L = 160 mm and L o =80 mm).
Finally, tensile tests were performed using specimens and testing conditions according to ASTM D638-14 on a Shimadzu testing machine model Autograph AGS-X. For each condition, three specimens were tested at constant head
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