PSI - Issue 37

S. Valvez et al. / Procedia Structural Integrity 37 (2022) 738–745 S. Valvez et al. / Structural Integrity Procedia 00 (2019) 000 – 000

744

7

In terms of flexural strength (Table 6), it is possible to observe different effects of the annealing treatment on this mechanical property. For PETG, for example, increasing the temperature increases the bending strength, but for all temperatures, when they remain constant and the exposure time increases, the bending strength decreases. In this case,

Table 7. The effect of the annealing treatment on the bending modulus.

PETG SD [MPa]

CFPETG

KFPETG

Samples Group

Average [MPa]

Variation [%]

Average [MPa]

SD [MPa]

Variation [%]

Average [MPa]

SD [MPa]

Variation [%]

Control

1.7 2.0 1.9 1.9 1.8 1.8 1.8 2.0 1.9 1.8

0.02 0.06 0.04 0.08 0.07 0.03 0.05 0.08 0.07 0.1

3.6 4.4 4.7 4.6 4.5 4.4 5.1 4.9 5.4 5.8

0.2 0.2 0.2 0.5 0.1 0.2 0.1

1.5 1.8 2.5 2.1 1.9 2.1 2.1 1.8 2.2 2.2

0.03 0.09 0.09 0.05 0.18 0.06 0.07 0.09 0.03 0.03

1 2 3 4 5 6 7 8 9

17.6 11.8 11.8

23.0 32.0 29.0 25.3 22.6 43.9 39.0 51.1 61.1

20.2 62.6 36.3 25.7 38.9 34.1 20.1 46.7 46.7

5.9 5.9 5.9

17.6 11.8

0.07

0.2 0.2

5.9

the increase in exposure time is negative for this mechanical property and the ideal values are up to 30 minutes of exposure. Regardless of temperature, an annealing treatment of 30 min only produces improvements around 10% higher than those seen in control samples. However, the benefits achieved are strongly counterbalanced by the geometric and dimensional changes, which were conveniently reported earlier. A similar analysis can be obtained from Table 7 for the PETG flexural modulus. Regarding the CFPETG composite, increasing both the temperature and exposure time promotes improvements in terms of bending strength and modulus. In this case, it is possible to achieve improvements around 31.8% higher than the value observed for control specimens, at level of bending strength, and 61.1%, at level of bending modulus, for an annealing treatment at 130 °C during 480 min of exposure. For the KFPETG composite, the same comments describe the trend observed in Tables 6 and 7, but with different values (11.1% and 46.7%, respectively). However, as mentioned above, this annealing treatment has a very destabilizing effect on the dimensional and geometric stability for both materials. 4. Conclusions Fused filament fabrication (FFF) proves to be one of the most attractive 3D printing technologies due to its low cost, simplicity, and high-speed processing. However, some disadvantages still affect the implementation of this technique in the most diverse sectors. The mechanical performance of these materials can, for example, be compromised due to a poor interfacial adhesion between the printed layers and, consequently, restrict the use of this technology for secondary structures. According to the literature, the use of annealing treatments can be a solution to get around this problem. In this context, the present study showed that annealing heat treatment can be a solution to improve the mechanical properties of PETG and PETG-based composites. It was noted that both the increase in temperature and exposure time promote a significant increase in flexural strength and modulus, reaching, respectively, values higher than those of control specimens around 31.8% and 61.1% for CFPETG composites and around 11.1% and 46.7% for KFPETG composites. However, the annealing treatment promotes geometric distortions and significantly affects the dimensional stability of the parts. Therefore, for design considerations that require dimensional and geometric stability, annealing treatments should be limited to a predetermined temperature and exposure time that are heavily dependent on the material used. On the other hand, this study showed benefits for 4D applications.