PSI - Issue 53

Alessandro Greco et al. / Procedia Structural Integrity 53 (2024) 178–184 Author name / Structural Integrity Procedia 00 (2019) 000–000

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1. Introduction PEEK (PolyEther Ether Ketone) is a semi-crystalline thermoplastic polymer belonging to the PAEK (Poly Aryl Ether Ketone) class. Among the other polymers of the same class, PEEK is the most used material in 3D printing because of its easy of machining and excellent mechanical properties, thermal stability, chemical and high-temperature resistance. PEEK parts can be produced by various technologies such as injection molding, machining or extrusions. Moreover, being biocompatible and recyclable, this makes PEEK widely used in several industries, including aerospace, automotive, biomedical, as reported in Citarella et al. (2021), Grassia et al.(2018, 2019). Additive Manufacturing (AM) processes represent cost-effective solutions, considering the possibility of higher customization and shape complexity. Specifically, the most interesting AM technology for producing PEEK is Fused Filament Fabrication (FFF), consisting in layer-by-layer building by continuously extruding the filament at its melting temperature. Additively manufactured PEEK, both natural and carbon fiber-reinforced, presents several challenges being highly sensitive to processing conditions alterations, which can cause high geometrical distortions, weak inter layer adhesion, porosity, etc. Thorough mechanical characterization of AM PEEK is essential for ensuring reliable performance in these applications (Stepashkin et al., 2018). This makes PEEK a material that needs extensive studies to make it suitable for structural applications. State of the art can count on several contributions on this topic: annealing, i.e., has been found to enhance the PEEK crystallinity, increase the mechanical strength and the elongation at break (He et al., 2023). Myllari et al. (2015) investigated on the effects of thermal degradation of PEEK. Short-term annealing was found to lead to increased mechanical performances because of the formation of secondary crystals. In Wu et al. (2015), authors investigated on the influence of layer thickness and raster angle on mechanical properties of PEEK. The optimal mechanical properties were found at a layer thickness of 300 μ m and a raster angle of 0°. Pulipaka et al. (2023) investigated on the processing parameters influencing the printed part. Among nozzle temperature, platform temperature, infill percentage, layer height, and print speed, nozzle temperature and layer height were found to influence for the most roughness and elastic modulus. No parameters were found to affect hardness and creep. In terms of effects on Young’s modulus, yield stress, ultimate tensile stress and resilience modulus, infill, platform temperature, nozzle temperature and layer height show the most influence. The outcomes of this study provide guidance for optimizing printing parameters and annealing post-processing treatment, facilitating the production of high-performance AM PEEK parts with enhanced mechanical properties.

Fig. 1. Schematization of considered layer height values and infill patterns.