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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From the results in Fig. 5, it can be observed that the tensile performance of specimens characterized by rectilinear infill pattern approaches that of molded PEEK. In particular, for series 2 and 4, the average values of Young’s moduli were 3.68 GPa and 3.65 GPa respectively. Young’s modulus is even slightly better than molded PEEK reference value (  3.60 GPa). The result for UTS is also satisfactory. Indeed, for series 2 and 4, average values of UTS were equal to 89.33 MPa and 87.64 MPa respectively, hence a little more than 10% lower than the molded PEEK reference value (  100 MPa). In contrast, elongation at fracture shows far lower performances than molded PEEK (  35 %), with average values equal to 7.65 % and 7.10 % for series 2 and 4 respectively. Concerning series 1 and 3, characterized by triangular infill pattern, the tensile performance are far from that of molded PEEK. Average values of Young’s moduli were equal to 3.41 GPa and 3.45 GPa respectively, whereas UTS average values were equal to 78 MPa and 75.35 MPa. Two samples belonging to series 3 were subjected to annealing post processing treatment, according to the temperature curve reported in Fig. 3. The following Fig. 6 shows the results of the tensile tests and a comparison of the performance with the series 3, having the same parameters configuration but not subjected to annealing. The annealed series exhibited a more fragile behavior than the non-post-treated series. In addition, by looking at Young's modulus and UTS, it appeared that, with this configuration of parameters, the treatment worsens the tensile performance of the material. Young’s modulus average value decreased of about 7.5 % (3.19 GPa), whereas UTS decreased of about 17 % (62.57 MPa). This result is not consistent with what reported in the literature (Zhen et al., 2023), (He et al., 2023) and (Wu et al., 2015), where it was found that annealing improved mechanical performance. However, comparing the tensile results with a similar parameter configuration (except for the chamber temperature), the mechanical performances achieved in this research with the specimens without annealing were superior and, in some cases, close to those of molded PEEK. The deterioration in performance after annealing could be due to a worsening effect on the crystallinity of the material or to the specific infill pattern (triangular in the case shown). In any case, further investigations are needed, perhaps by considering additional infill patterns and including fatigue tests (D’Amore et al., 2019).

Fig. 6. Comparison of tensile properties between series 3 (not annealed) and series 7 (annealed): (a) stress-strain curves; (b) Young’s modulus (E); (c) Ultimate Tensile Stress (UTS).