: A Study on the Influence of FDM Parameters on the Tensile Behavior of Samples made … A Study on the Influence of FDM Parameters on the Tensile Behavior of Samples made of PET-G

This experimental study investigated the influence of FDM 3D printing parameters on the tensile behavior of PET-G-made parts. In this context, 27 test specimens were produced using FDM on the Anycubic 4 Max Pro 2.0 printer with layer heights applied in one pass L h = 0.10/0.15/0.20 mm and filling percentages I d = 50/75/100 %. All these samples were tensile tested on the Barrus White 20 kN universal testing machine. The experimental results determined maximum tensile strength, elongation percentage at break, and Young's modulus. The two parameters considered, I d and L h , influence the maximum tensile strength, the elongation percentage at break, and Young's modulus. The findings demonstrated that the filling percentage has a strong influence on the maximum tensile strength and the elongation percentage at break of the PET-G samples, and L h has a decisive influence on Young's modulus.


INTRODUCTION
Additive manufacturing technologies have revolutionized a part of the manufacturing processes, introducing a new concept of adding material in overlapping layers.The former have been adopted worldwide by key industries, such as aerospace, energy, medical, automotive, and manufacturing [1][2][3].Additive manufacturing technologies emerge over conventional manufacturing technologies (subtractive and formative technologies) with the following main advantages: the ability to change the shape of the finished product without constraints, ease of use, energy efficiency, and environmental impact [2,[4][5][6][7][8][9][10].However, additive manufacturing technologies have certain limitations, namely printing speed, part surface quality, and mechanical characteristics that are inferior to parts made with conventional technologies [11][12][13].
The mechanical features of the parts are of great importance and it is necessary to optimize the printing parameters to obtain their maximum values.The main FDM parameters that contribute to the mechanical characteristics of parts are the height of the layer applied in one pass (L h ), the filling percentage (I d ), the printing speed (P s ), the filling pattern (I p ), the part orientation, the extruder temperature (E t ), and the table temperature (B t ) [14][15][16][17][18][19][20][21][22][23][24][25][26].
In [14], the influence of the FDM parameters (height of the layer applied in one pass and filling percentage) on the tensile strength and hardness of PLA parts was studied.The outcomes showed that better results were obtained with an increase in the filling percentage.In [15], the influence of the height of the layer applied in one pass and the color of the filament on the dimensional accuracy and tensile strength of FDM PLA parts was studied.According to the findings, the tensile strength decreases with increasing L h and the color of the filament has an impact on tensile strength, as the FDM-made specimens from gray and red colored filaments had better mechanical characteristics compared to those made with black and natural colored filaments.In [16], a study on the optimization of FDM printing parameters to improve the tensile properties of parts produced from ABS and nylon was presented, varying three parameters: I p (tri-hexagonal, triangular, octet), I d (10/50/100%) and P s (60/65/70 mm/s).The results exhibited that among the three parameters studied, I d had a strong influence on tensile strength since it increased with a higher I d .In [27], the mechanical and durability performance of concrete with different doses of bacteria were investigated.The results disclosed that bacteria can improve the physical properties of cement concrete.In [28], the effect of different gradations of coarse aggregates on the mechanical properties of No-Fines Concrete (NFC) was studied, showing that the aggregate gradation significantly affects the compressive, splitting tensile, and flexural strength of NFC.In [29], an experimental study was carried out on NFC with a fixed proportion of cement-toaggregate (c-a) of 1:6 with a 0.40 water/cement (w/c) ratio.It was discovered that the aggregate classification, the c-a ratio, and the w/c ratio have a significant impact on compressive strength.In [30], the influence of FDM process parameters (air gap, extruder temperature, layer thickness, infill density, and raster angle) on the tensile strength of parts printed with PLA material was investigated.The findings demonstrated that layer thickness and infill density have a direct impact on tensile strength and percentual elongation, and the best result for tensile strength was for the sample with the highest infill density.
This study aims to determine the influence of FDM on the tensile behavior of samples made of PET-G and to present the optimal combination of parameters for the best tensile strength results.Statistical analysis was performed on the findings using Minitab for a better understanding of the effects of FDM parameters on the tensile behavior of PET-G-made samples.The samples were produced and tested in laboratories of the Faculty of Mechanical and Electrical Engineering of the Petroleum-Gas University of Ploiești.II.EXPERIMENTAL METHOD Figure 1 illustrates the steps of the method used to investigate the influence of FDM parameters on the tensile behavior of PET-G parts.Solidworks 2023 [31] was used to create the 2D and then the 3D model of the tensile specimen, shown in Figure 2. The 3D model of the specimen was converted from SLD to STL format.The STL file, which corresponds to the specimen depicted in Figure 2, was processed in Cura Slicer software [32] by choosing the PET-G material and entering the FDM printing parameters from Table I, followed by the generation of the G-Code file.By utilizing Minitab software [34] and the FDM parameters in Table I, L h = 0.10/0.15/0.20 mm and I d = 50/75/100%, the contour plot of the tensile strength of PET-G tensile specimens, pinpointed in Figure 10, was plotted [5].Analysing the contour plot in Figure 10 led to an observation of how the L h and I d parameters of the FDM affect the specimen tensile strength.By increasing the filling percentage (I d ) it can be observed that this augmentation has a significant impact on the increase in tensile strength of PET-G tensile specimens.Fig. 6.
PET-G specimens after tensile testing.

C. Influence of FDM Parameters on Young Modulus Values
Obtained in the Tensile Test of PET-G Specimens

Fig. 1 .
Fig. 1.The steps of the method used to investigate the influence of FDM parameters on the tensile behavior of PET-G parts.

Fig. 7 .
Fig. 7.Mean values of the tensile strength of PET-G specimens.

Fig. 8 .
Fig. 8. Pareto chart of the influence of the parameters A = Lh and B = Id on the tensile strength of PET-G tensile specimens.

Figure 10
Figure 10 presents the average values of the elongation percentage at break acquired from the tensile testing of the

Fig. 10 .
Fig. 10.Mean values of elongation percentage at break of PET-G specimens.The Pareto chart shown in Figure 11 was plotted using Minitab and demonstrates that the filling percentage (B = I d ) strongly influences the elongation percentage at break of PET-G-made specimens.

Fig. 11 .
Fig. 11.Pareto chart showing the influence of the parameters A = Lh and B = Id on the percentage elongation at break of PETG tensile specimens.

Figure 12
Figure 12 exhibits a contour plot of the elongation percentage of the specimens.It can be observed how the L h and I d of the FDM influence the elongation percentage at specimen break.Increasing I d has the main influence on increasing the elongation percentage at break of PET-G tensile specimens.

Fig. 12 .
Fig. 12. Contour plot of percentage elongations at break of PET-G tensile specimens.

Figure 13
Figure 13 displays the average Young modulus values obtained from tensile testing of the specimens.The FDM parameters affect the Young modulus values.The best result, 0.62 GPa, was acquired for specimens with I d = 100% and the height of the layer applied at one pass L h = 0.10 mm.By increasing I d from 50 to 75%, the Young modulus values increased by 11.93-21.08%, and by increasing I d from 75 to 100%, the Young modulus values increased by 5.31-7.67%.When decreasing the L d applied from 0.20 to 0.15 mm, the Young modulus values increased by 4.33-24.04%,and when decreasing from 0.15 to 0.10 mm, the Young modulus values increased by 0.56-13.65%.

Fig. 13 .
Fig. 13.Average values of Young modulus obtained in tensile test of PET-G specimens.

Figure 14
Figure 14 depicts a Pareto chart, indicating that the height of the layer applied at one pass (A=L h ) has the greatest influence on the Young modulus values obtained in the tensile test of PET-G specimens.Figure 15 portrays a contour plot of the Young modulus values acquired in the tensile test of PET-G specimens.It can be observed how increasing I d and decreasing L h determine an increase in the Young modulus values obtained in the tensile test of PET-G specimens.

Fig. 14 .
Figure 14 depicts a Pareto chart, indicating that the height of the layer applied at one pass (A=L h ) has the greatest influence on the Young modulus values obtained in the tensile test of PET-G specimens.Figure 15 portrays a contour plot of the Young modulus values acquired in the tensile test of PET-G specimens.It can be observed how increasing I d and decreasing L h determine an increase in the Young modulus values obtained in the tensile test of PET-G specimens.

Fig. 15 .
Fig. 15.Contour plot of Young modulus obtained in tensile test of PET-G specimens.IV.CONCLUSIONS The study investigated the influence of 3D FDM printing parameters on the tensile behavior of parts made of Everfill brand PET-G.In this context, 27 FDM-made specimens on the Anycubic 4 Max Pro 2.0 with layer heights applied at a pass L h = 0.10/0.15/0.20 mm and filling percentage I d = 50/75/100% were tensile tested on a Barrus White 20 kN universal testing machine.The parameters I d and L h influence the tensile behavior (tensile strength, percentage elongation at break, and Young modulus) of 3D-printed PET-G specimens.Increasing the filling percentage (I d ), increases the break strength of the specimens.This agrees with the results of [14, 16, 30].By comparing the outcomes of this study to [14], the tensile strength of PET-G for I d = 50/75/100% is less than the tensile strength of PLA with the same fill density with 31.10-56.22/16.50-44.05/18/60-58.14%.The minimum value of the tensile strength of the PET-G FDM specimens, 15.48 MPa, was recorded when using L h = 0.20 mm and I d = 50%, and the maximum value of the tensile strength, 28.25 MPa, was recorded for L h = 0.10 mm and I d = 100%.Increasing the filling percentage (I d ) increased the elongation percentage of the specimens made by PET-G FDM.