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Effects of fused deposition modeling process parameters on tensile, dynamic mechanical properties of 3D printed polylactic acid materials
Polymer Testing 86 (2020) 106483
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Polymer Testing journal homepage: http://www.elsevier.com/locate/polytest
Effects of fused deposition modeling process parameters on tensile, dynamic mechanical properties of 3D printed polylactic acid materials Shuheng Wang a, b, Yongbin Ma a, b, Zichen Deng a, b, *, Sen Zhang a, b, Jiaxin Cai a, b a b
School of Mechanics, Civil Engineering and Architecture, Northwestern Polytechnical University, Xi’an, 710072, PR China MIIT Key Laboratory of Dynamics and Control of Complex Systems, Northwestern Polytechnical University, Xi’an, 710072, PR China
A R T I C L E I N F O
A B S T R A C T
Keywords: Fused deposition modeling Process parameters Tensile properties Dynamic mechanical properties
Fused deposition modeling (FDM) is an important process among the available additive manufacturing tech nologies in various industries. Although there exists many works investigating the effects of FDM process pa rameters on the mechanical properties of printed materials, there are still several points need to be studied. One is the effects of process parameters on the dynamic mechanical properties of FDM-printed materials, especially in environments where the temperature often changes. The other is the mechanism by which process parameters affect the mechanical properties of printed materials. Aiming at these two points, uniaxial tensile tests and dynamic mechanical analysis are carried out respectively to characterize the tensile properties and dynamic mechanical properties of FDM-printed PLA materials under different FDM process parameters, namely printing angle, layer thickness, fill rate and nozzle temperature. Based on the experimental results explanations are given for the influence of the FDM process parameters on the mechanical properties of the printed materials.
1. Introduction Compared with conventional processing methods, additive manufacturing (AM) is based on an incremental layer by layer manufacturing, which not only can quickly manufacture lightweight and complex structures [1–3] but also enables printing of multi-materials [4,5]. Therefore, applications of AM technology are emerging in several fields, such as aerospace [6], medicine [7], civil construction [8] and food production [9]. Fused Deposition Modeling (FDM) is an AM process based on extrusion, the material being “selectively dispensed through a nozzle or orifice” [10]. In recent years, FDM has become one of the most popular AM technologies due to its easy of use, low cost, and that it is able to process thermoplastic polymers such as ABS, PLA, PC, PS, Nylon and PET [11,12]. However, since the FDM-printed materials are deposited layer by layer, the interlayer bonding is weak, resulting in poor me chanical properties compared with injection molded [13]. There are many process parameters that can be set in the FDM process, which will affect the mechanical properties of the final product. Therefore, it is necessary to have a deeper understanding of the FDM process in order to improve the mechanical properties of the printed material by setting reasonable process parameters.
A relatively large amount of work has been done to investigate the effects of process parameters on the mechanical properties of the FDMprinted materials under static loading [14–19]. Popescu et al. [14] reviewed the effects of different FDM process parameters on different mechanical properties such as tensile, compressive and flexural strength of materials and concluded that the key parameter influencing FDM parts’ mechanical properties are: raster-to-raster air gap, raster angle, layer thickness, infill density and build orientation. In the meantime, Popescu et al. [14] also emphasized that some process such as nozzle and bed temperature were insufficiently studied and the variability in the mechanical properties noted by many authors should be analyzed more deeply and explained in further research work. Jha and Nar asimhulu [15] mentioned that other mechanical properties such as creep and vibration need to be studied. The transversely isotropic elastic model and the Hill anisotropic yield model were used by Yao et al. [16] and Xia et al. [17] to describe the tensile mechanical properties of FDM materials, mainly considering the influence of printing angle. In the work of Gordelier et al. [18], tensile strength can be maximized by improving various process parameters, but the research on printing temperature is insufficient. Researchers’ interests are focused on opti mizing process parameters and establishing theoretical models, and very little work has been done to understand the mechanics of the effects of
* Corresponding author. School of Mechanics, Civil Engineering and Architecture, Northwestern Polytechnical University, Xi’an, 710072, PR China. E-mail address: [email protected] (Z. Deng). https://doi.org/10.1016/j.polymertesting.2020.106483 Received 21 January 2020; Received in revised form 7 March 2020; Accepted 7 March 2020 Available online 10 March 2020 0142-9418/© 2020 Elsevier Ltd. All rights reserved.
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process parameters on mechanical properties. In addition, most litera tures only study the effect of FDM process parameters on the mechanical properties of materials under static loading and ignore the fact that FDM-printed materials may exhibit viscoelastic properties when the materials undergo cyclic deformation under dynamic loading condi tions. In applications such as the automotive industry, most FDM-printed materials are subject to dynamic stress, deformation, and vibration, which can make parts prone to failure, especially at higher temperatures [20]. Therefore, it is necessary to analyze the dynamic mechanical properties of FDM-printed materials. At present, related research focuses on the effects of FDM processes and reinforcing filler on the dynamic properties of FDM-printed mate rials. Based on I-optimal response surface methodology and Q-optimal design, Mohamed et al. [20,21] optimized the dynamic mechanical properties of FDM-printed PC-ABS materials under different FDM pro cesses (layer thickness, air gap, raster angle, build orientation, road width and number of contours). Mansour et al. [22] and Coppola et al. [23] respectively used graphene and clay as reinforcing filler to study their effects on the dynamic mechanical properties of FDM-printed PLA materials. Coppola et al. also studied the effect of nozzle temperature (185-200-215 � C for PLA 4032D and 165-180-195 � C for PLA 2003D) on the dynamic mechanical properties of FDM-printed PLA materials. Taguchi approach was used by Miquel et al. [24] to investigate the in fluence of nozzle diameter on the dynamic mechanical properties of FDM-printed PC materials under different temperatures and frequencies. However, in the above studies, attention was not focused on the mechanism by which the FDM process affects the printed material’s dynamic mechanical properties and process parameters such as tem perature and nozzle diameter often change only two to three times, which sometimes misses some important phenomena. Therefore, it is important to understand how the process parameters affect the static and dynamic mechanical properties of materials. In this paper, four FDM process parameters, namely printing angle, layer thickness, fill rate and nozzle temperature, are selected and reasonably set to better understand the effects of FDM process param eters on the mechanical properties of FDM-printed PLA materials. Considering that PLA exhibits viscoelastic properties and may undergo cyclic deformation under dynamic loading conditions in practical ap plications, dynamic mechanical analysis (DMA) and uniaxial tensile tests are carried out to characterize the tensile properties and dynamic mechanical properties of the FDM-printed PLA materials. Due to the obvious viscosity characteristics of PLA materials at higher tempera tures, the dynamic mechanical properties of FDM-printed PLA materials at different temperatures are also analyzed.
PolyPlus PLA filament with a diameter of 1.75 mm is supplied by Polymaker Industry (China, Shanghai). PolyPlus PLA has good color performance, does not block the nozzle, and provides very stable performance. 2.2. Uniaxial tensile tests The uniaxial tensile tests are carried out in the AGS-X computercontrolled electronic universal testing machine. According to ISO 527-22012 (International standard, plastics determination of tensile proper ties Part 2: Test conditions for moulding and extrusion plastics), the tensile specimens used in the study are designed and fabricated (Fig. 2). The uniaxial tensile experiment setup is shown in Fig. 3 (a). The tensile speed is 2 mm/min and the temperature keep 23 � C during the whole tensile course. So, the test condition can be confirmed to be quasi-static loading and in normal temperature. The extensometer with gauge length of 50 mm is used here to measure the elastic modulus and elongation at break more conveniently. 2.3. Dynamic mechanical analysis Dynamic mechanical analysis is an indispensable and effective tool for determining the dynamic parameters of polymers and composites under cyclic external forces [25]. Dynamic parameters such as storage modulus E’ , loss modulus E’’ , and loss factor tan δ are temperature dependent and have following relationship: tan δ ¼
3. Results and discussions According to Table 2, for each number, five specimens were prepared for uniaxial tensile tests and three specimens were prepared for DMA tests. There are respectively 94 and 63 sets of experimental data are valid, and the average of the experimental results are listed in Table 2 (Because the dynamic mechanical properties of materials change with temperature, only the maximum values are listed). In order to reflect the effects of process parameters on the tensile properties and the dynamic mechanical properties of the FDM-printed PLA materials more clearly, the data in Table 2 is plotted in Fig. 4 and Fig. 8.
2.1. 3D printing machine and printing materials Raise3D Pro2 Plus 3D printer is used to fabricate the specimens. The specimens are designed with SolidWorks 2014® (Dassault Systems SolidWorks Corp, USA) and exported as stl format into the 3D printer software (ideaMaker v.3.4.2, Raise 3D, China). The nozzle diameter of 0.4 mm is selected, and the main structure and the support structure are printed by the same nozzle. This paper mainly studies the effects of four FDM process parameters, namely printing angle, layer thickness, fill rate and nozzle temperature, on the tensile properties and dynamic me chanical properties of FDM materials. The default FDM process param eters are listed in Table 1. The four parameters studied are set as listed in Table 2. The printing angle is illustrated in Fig. 1.
3.1. Effects of process parameters on tensile properties 3.1.1. Effects of printing angle Printing angle influences the anisotropy of the FDM parts. As show in Fig. 4, printing angle has a great influence on the tensile properties of FDM-printed PLA materials, especially the tensile strength and elonga tion at break. The elastic modulus, tensile strength and elongation at break of the FDM-printed PLA materials increase with the increase of the printing angle. This is because the printing angle directly affects the fracture mode of the FDM-printed PLA materials, that is, the interlayer fracture or the intra-layer fracture. The fracture characteristics of the specimens printed in different angles after the uniaxial tensile tests are shown in Fig. 5 (a). When the printing angle is less than 45� , the failure mode of the specimens is interlayer fracture, and when the printing angle is greater than 45� , the failure mode of the specimens is intra-layer fracture. It is noticeable that when the printing angle is 45� , inter-layer
Table 1 Default FDM process parameters. Bed temperature (� C)
Fill Type
Support fill rate (%)
60
60
Grid
30
(1)
Dynamic mechanical properties of FDM-printed PLA materials are measured in tensile mode using a DMA þ450 (01 dB-Metravib, France). Temp Ramp/Freq Sweep test in Multifrequency Strain method is used for dynamic mechanical tests. Tests are carried out under the tempera ture range from 30 � C to 90 � C with a heating rate of 3 � C/min and amplitude of 20 μm at a fixed frequency of 1 Hz in nitrogen atmosphere. DMA experiment set up is shown in Fig. 3 (b). Storage modulus, loss modulus and loss factor are recorded as a function of temperature.
2. Materials and methods
Printing speed (mm/s)
E’’ E’
2
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Table 2 FDM process parameters settings and experimental results. Number
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
FDM process parameter
Average of effective experimental results
Printing angle (� )
Layer thickness (mm)
Fill rate (%)
Nozzle temperature (� C)
Elastic modulus (MPa)
Tensile strength (MPa)
Elongation at break (%)
Storage modulus (MPa)
Loss modulus (MPa)
Loss factor
0 15 30 45 60 75 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90
0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.05 0.15 0.20 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10
100 100 100 100 100 100 100 100 100 100 20 40 60 80 100 100 100 100 100 100 100
210 210 210 210 210 210 210 210 210 210 210 210 210 210 195 200 205 215 220 225 230
2257.98 2287.97 2304.84 2377.18 2389.54 2407.83 2422.63 2460.85 2402.13 2367.90 1459.06 1507.83 1692.26 2005.71 2248.00 2332.67 2359.56 2464.26 2443.75 2431.77 2424.96
27.48 30.69 32.35 37.42 43.93 49.85 53.66 53.70 51.75 50.52 20.04 21.08 23.81 28.50 46.97 47.30 49.18 54.39 54.17 54.27 53.03
1.35 1.47 1.57 2.27 4.39 4.91 5.36 6.28 5.20 4.81 3.50 3.84 4.56 4.66 3.96 4.40 5.02 5.30 4.76 3.10 2.64
2913.51 3132.21 3174.30 3183.19 3216.27 3268.91 3344.07 3377.32 3202.52 3042.90 2408.89 2811.45 2852.44 3000.11 3275.12 3325.09 3314.92 3445.20 3254.61 3259.21 3250.33
501.20 531.12 525.31 549.22 525.89 517.06 525.01 537.34 518.23 512.09 402.11 450.78 465.31 511.18 512.43 521.68 517.24 569.34 554.15 551.09 530.03
2.96 2.98 3.01 3.06 3.01 2.93 2.94 3.02 2.90 2.86 2.78 2.85 2.90 2.92 2.80 2.88 2.88 3.24 3.08 3.02 2.98
The greater the layer thickness, the greater the distance between the nozzle and the deposited material during extrusion, resulting in less pressure between them. Therefore, an increase in the layer thickness causes a decrease in the mass of the deposited material of the same height and an increase in the interlayer air gaps, thereby reducing the interlayer bonding strength of the FDM-printed PLA materials [26]. Similarly, the bonding strength between the extruded filaments is also reduced. In addition, when the printing speed is constant, the increase of the layer thickness will reduce the cooling time of the material and affect the adhesion between the layers, which will further reduce the tensile properties of the printed materials. Since the layer thickness mainly affects the interlayer bonding strength of the printed material, it can be inferred that the smaller the printing angle, the greater the printed material’s tensile strength is affected by the layer thickness. In order to prove this, the tensile strength of standard test specimens with different printing angles at a layer thickness of 0.2 mm was additionally tested. The fracture characteristics of the specimens are shown in Fig. 5 (b), and the comparison of the tensile strength of printed PLA materials with different printing directions at a layer thickness of 0.1 mm and 0.2 mm is shown in Fig. 6. Different from Fig. 5 (a), obviously inter-layer fracture can be observed in Fig. 5 (b) when the printing angle is 45� , which may indicate that inter-layer failure is more likely to occur under tensile load when the layer thickness increases.
Fig. 1. Schematic diagram of printing angle.
fracture and intra-layer fracture occur simultaneously. The interlayer fracture strength depends mainly on the interlayer bonding strength, and the intra-layer fracture depends mainly on the strength of the extruded material. It is apparent that the interlayer bonding strength of the FDM-printed PLA materials is lower than the PLA’s strength. 3.1.2. Effects of layer thickness Layer thickness is a feature parameter in FDM process, which not only has a great influence on the printing time, but also greatly in fluences the precision and mechanical properties of the FDM-printed materials. As shown in Fig. 4, the elastic modulus, tensile strength and elongation at break decrease with the increase of the layer thickness.
3.1.3. Effects of fill rate Fill rate determines the effective cross-sectional area in the tensile direction and interlayer bonding strength of the FDM-printed materials, thus influencing the mechanical properties of the printed materials. As the fill rate increases, the air gaps in the material decrease and the
Fig. 2. The dimension of FDM-printed specimens for uniaxial tensile test. 3
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Fig. 3. (a) Uniaxial tensile experiment set up, (b) DMA experiment set up.
effective cross-sectional area increases [27]. Therefore, it can be seen from Fig. 4 that the elastic modulus, tensile strength, and elongation at break greatly increase as the fill rate increases.
the relaxation of polymer chains, because in polymers, the tendency of energy storage decreases with increasing temperature, and the tendency of loss of energy increases with increasing temperature [30]. For the loss modulus, when temperature rises from 30 � C to 55 � C, it first decreases slowly and then slowly rises. The loss modulus increases quickly when temperature exceeds 55 � C and reaches the maximum at around 59.7 � C after nearly two order of increase. Then the loss modulus decreases quickly by nearly three orders of magnitude. After the tem perature exceeds 67 � C, the loss modulus decreases slower and slower. The tendency of the loss factor to change with temperature is very similar to the loss modulus, only the values are different. When tem perature rises from 30 � C to 57 � C, the loss factor first decreases slowly and then slowly rises. The loss modulus increases quickly when tem perature exceeds 57 � C and reaches the maximum at around 64 � C after two order of increase. When the temperature rises to 80 � C, the loss factor decreases by an order of magnitude and then the decrease speed becomes slower and slower.
3.1.4. Effects of nozzle temperature Nozzle temperature mainly affects the fluidity of extruded material. When the nozzle temperature is too low, due to the poor fluidity of the extruded material, it cannot adhere well to the deposited material, which often leads to unsuccessful printing. When the nozzle temperature is too high, the extruded PLA material is almost liquid or even partially thermally degraded [28,29]. Since the printing speed is unchanged, the previous layer of material has not completely solidified, and the next layer of material starts to print, which will affect the printing accuracy and affect the mechanical properties of the material [26]. As shown in Fig. 4, when the nozzle temperature is raised from 195 � C to 210 � C, the elastic modulus, tensile strength and elongation at break of the printed material increase as the fluidity and bonding strength of the extruded material increase. When the nozzle temperature is raised from 210 � C to 230 � C, the elastic modulus and tensile strength of the material decrease slightly, and the elongation at break decreases rapidly. This may be because the fluidity of the extruded material is too large to guarantee the surface quality of the material and thereby reduce the elongation at break of the material. At the same time, thermal degradation of the PLA material due to higher nozzle temperatures also reduces the mechanical properties of the material. Therefore, by setting the nozzle temperature to 210 � C–215 � C, the mechanical properties of the FDM-printed mate rial will be better.
3.2.1. Effects of printing angle It can be seen from Fig. 8 that the printing angle has a relatively large influence on the dynamic properties of the FDM-printed PLA materials. In general, the storage modulus trends to increase as the printing angle increases. The maximum and minimum values of the storage modulus correspond to printing in the horizontal direction and printing in the vertical direction, respectively. However, the loss modulus and the loss factor first increase and then decrease as the printing angle increases, and reach a maximum in the 45� direction. Similar phenomenon can be seen from previous work [20,31]. Therefore, when subjected to dynamic loading, PLA materials printed in 90� may have more store load po tential, and PLA material printed in 45� may have more potential to dissipate energy rather than storing it.
3.2. Effects of process parameters on dynamic mechanical properties Taking the number 7 experimental data as an example, the measured storage modulus, loss modulus and loss factor are plotted as a function of temperature is shown in Fig. 7. Based on the experimental data, the dynamic mechanical properties of the FDM-printed PLA materials have following characteristics when the temperature rises from 30 � C to 90 � C. The storage modulus decreases with increasing temperature. When temperature rises from 30 � C to 55 � C, the storage modulus decreases slowly (approximately by 7%). However, when the temperature exceeds 55 � C, the storage modulus begins to decrease dramatically. Up to 63 � C, the storage modulus decreased by three orders of magnitude, with the fastest decrease speed at around 59.7 � C. After the temperature exceeds 63 � C, the storage modulus decreases slower and slower. This is due to
3.2.2. Effects of layer thickness Layer thickness also has significant influence on the dynamic me chanical properties of the FDM-printed PLA materials. It can be seen from Fig. 8 that the storage modulus, loss modulus, and loss factor of the FDM-printed PLA materials decrease with increasing layer thickness. This result is consistent with the published study [31]. As mentioned earlier, the smaller the layer thickness, the greater the bonding strength between layers and filaments, resulting in greater stiffness. In the pro cess of dynamic cyclic loading, the smaller layer thickness may have greater constraints on the movement of adjacent polymer chains in PLA, and the loss modulus and loss factor may also be larger. 4
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Fig. 4. Effects of FDM process parameters on (a) elastic modulus, (b) tensile strength, and (c) elongation at break.
3.2.3. Effects of fill rate It is shown in Fig. 8 that as the fill rate increases, the storage modulus and loss modulus of FDM-printed PLA materials increase rapidly, and the loss factor increases relatively slowly. This observation is consistent with the pervious study [20,21,23]. The possible explanation is that with the increase of the fill rate, the air gaps in the material decrease rapidly, which makes the material layers and the filaments more tightly bonded, and the PLA molecular segment movement resistance increases. This not only increases the storage modulus of the printed material, but also increases its loss modulus and loss factor.
especially the loss factor of the material. The storage modulus, loss modulus and loss factor of the material first increase and then decrease with the increase of the nozzle temperature, and reach the maximum at about 215 � C. Compared with the effect of nozzle temperature on the elastic modulus and tensile strength, the dynamic mechanical properties of the FDM-printed PLA materials decrease significantly when the temperature exceeds 215 � C. In previous study [23], the nozzle tem perature was set relatively low (185-200-215 � C for PLA 4032D and 165-180-195 � C for PLA 2003D), so it was only concluded that the dy namic mechanical properties of the FDM-printed material increased as the nozzle temperature increased. Therefore, it can be speculated that when the nozzle temperature is high, the thermal degradation of the PLA material may have a greater influence on the dynamic mechanical properties.
3.2.4. Effects of nozzle temperature Similar to the effect on tensile properties, the nozzle temperature has a greater impact on the dynamic mechanical properties of the material, 5
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Fig. 5. Fracture characteristics of the specimens.
4. Conclusions In this paper, it is found through experiments that the FDM process parameters will affect the mass of the printed material, the interlayer bonding strength, air gaps, etc., and these are the main reasons leading to the different mechanical properties of the printed material. Printing angle mainly affects the fracture mode of the FDM-printed PLA mate rials. When the printing angle is less than 45� , the failure mode of the specimen trends to be interlayer fracture, and conversely, the speci men’s failure mode trends to be intra-layer fracture. Layer thickness mainly affects the interlayer bonding strength of the printed materials. Smaller layer thickness not only strengthen the PLA materials’ interlayer bonding strength, but also may have greater restrictions on the move ment of adjacent polymer chains in PLA materials. The fill rate mainly affects the air gap inside the printed material. With the increase of the fill rate, the air gaps in the material decrease rapidly, which makes the material layers and the filaments more tightly bonded, and increases the resistance of the molecular chain of PLA materials. Nozzle temperature mainly affects the fluidity of extruded material. When the nozzle tem perature is too low, the fluidity of the extruded material is poor, which results in weak interlayer bonding strength. When the nozzle tempera ture is too high, the extruded PLA material is almost liquid, and even partial thermal degradation will occur, which is not conducive to printing.
Fig. 6. Tensile strength of printed PLA materials with different printing di rections at a layer thickness of 0.1 mm and 0.2 mm.
Data availability statement All the raw data required to reproduce these findings have already shown in this paper. Meanwhile, authors declare that their research content and experimental data are true and reliable. Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. CRediT authorship contribution statement Shuheng Wang: Methodology, Validation, Investigation, Writing original draft. Yongbin Ma: Conceptualization, Investigation, Writing -
Fig. 7. Dynamic mechanical properties as functions of temperature. 6
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Fig. 8. Effects of FDM process parameters on (a) storage modulus, (b) loss modulus, and (c) loss factor.
review & editing. Zichen Deng: Conceptualization, Investigation, Writing - review & editing, Funding acquisition. Sen Zhang: Data curation, Investigation. Jiaxin Cai: Data curation, Investigation.
References [1] B.G. Compton, J.A. Lewis, 3D-Printing of lightweight cellular composites, Adv. Mater. 26 (34) (2014) 5930–5935, https://doi.org/10.1002/adma.201401804. [2] J. Souza, A. Großmann, C. Mittelstedt, Micromechanical analysis of the effective properties of lattice structures in additive manufacturing, Addit. Manuf. 23 (2018) 53–69, https://doi.org/10.1016/j.addma.2018.07.007. [3] S.H. Wang, Y.B. Ma, Z.C. Deng, K. Zhang, S. Dai, Implementation of an elastoplastic constitutive model for 3D-printed materials fabricated by stereolithography, Addit. Manuf. (2020), https://doi.org/10.1016/j.addma.2020.101104. [4] M.A. Skylar-Scott, J. Mueller, C.W. Visser, J.A. Lewis, Voxelated soft matter via multimaterial multinozzle 3D printing, Nature 575 (2019) 330–348, https://doi. org/10.1038/s41586-019-1736-8. [5] W.F. Hao, Y. Liu, H. Zhou, H.S. Chen, D.N. Fang, Preparation and characterization of 3D printed continuous carbon fiber reinforced thermosetting composites, Polym. Test. 65 (2018) 29–34, https://doi.org/10.1016/j.polymertesting.2017.11.004.
Acknowledgements This work was supported by the National Key R&D Program of China (2017YFB1102801), the National Natural Science Foundation of China (grant numbers: 11602021), the Natural Science Basic Research Plan in Shaanxi Province of China (grant number: 2019JM-220), and Innova tion Foundation for Doctor Dissertation of Northwestern Polytechnical University.
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S. Wang et al.
Polymer Testing 86 (2020) 106483 [19] L. Wang, D.J. Gardner, Effect of fused layer modeling (FLM) processing parameters on impact strength of cellular polypropylene, Polymer 113 (2017) 74–80, https:// doi.org/10.1016/j.polymer.2017.02.055. [20] O.A. Mohamed, S.H. Masood, J.L. Bhowmik, Characterization and dynamic mechanical analysis of PC-ABS material processed by fused deposition modelling: an investigation through I-optimal response surface methodology, Measurement 107 (2017) 128–141, https://doi.org/10.1016/j.measurement.2017.05.019. [21] O.A. Mohamed, S.H. Masood, J.L. Bhowmik, Mathematical modeling and FDM process parameters optimization using response surface methodology based on Qoptimal design, Appl. Math. Model. 40 (2016) 10052–10073, https://doi.org/ 10.1016/j.apm.2016.06.055. [22] M. Mansour, K. Tsongas, D. Tzetzis, Measurement of the mechanical and dynamic properties of 3D printed polylactic acid reinforced with graphene, Polym. Plast. Technol. Eng. (2018) 1–11, https://doi.org/10.1080/03602559.2018.1542730. [23] B. Coppola, N. Cappetti, L.D. Maio, P. Scarfato, L. Incarnato, 3D printing of PLA/ clay nanocomposites: influence of printing temperature on printed samples properties, Materials 11 (10) (2018), https://doi.org/10.3390/ma11101947, 1947. [24] M. Domingo-Espin, S. Borros, N. Agullo, A.A. Garcia-Granada, G. Reyes, Influence of building parameters on the dynamic mechanical properties of polycarbonate fused deposition modeling parts, 3D Print. Addit. Manuf. 1 (2) (2014) 70–77, https://doi.org/10.1089/3dp.2013.0007. [25] N. Saba, M. Jawaid, O.Y. Alothman, M.T. Paridah, A review on dynamic mechanical properties of natural fibre reinforced polymer composites, Construct. Build. Mater. 106 (2016) 149–159, https://doi.org/10.1016/j. conbuildmat.2015.12.075. [26] X.Y. Tian, T.F. Liu, C.C. Yang, Q.R. Wang, D.C. Li, Interface and performance of 3D printed continuous carbon fiber reinforced PLA composites, Compos. Appl. Sci. Manuf. 88 (2016) 198–205, https://doi.org/10.1016/j.compositesa.2016.05.032. [27] K.L. Alvarez, R.F. Lagos, M. Aizpun, Investigating the influence of infill percentage on the mechanical properties of fused deposition modelled ABS parts, Ing. Invest. 36 (3) (2016) 110–116. [28] G.L. Re, S. Benali, Y. Habibi, J.M. Raquez, P. Dubois, Stereocomplexed PLA nanocomposites: from in situ polymerization to materials properties, Eur. Polym. J. 54 (2014) 138–150, https://doi.org/10.1016/j.eurpolymj.2014.03.004. [29] L.T. Sin, A.R. Rahmat, W.A.W.A. Rahman, Thermal Properties of Poly (Lactic Acid). Polylactic Acid: PLA Biopolymer Technology and Applications. Book Series: PDL Handbook Series, 2013, pp. 109–141. [30] M. Rubinstein, R.H. Colby, Polymer Physics, Oxford University Press, 2003. [31] O.A. Mohamed, S.H. Masood, J.L. Bhowmik, Analytical modelling and optimization of the temperature-dependent dynamic mechanical properties of fused deposition fabricated parts made of PC-ABS, Materials 9 (11) (2016) 895, https://doi.org/10.3390/ma11101947.
[6] L.E. Murr, Frontiers of 3D printing/additive manufacturing: from human organs to aircraft fabrication, J. Mater. Sci. Technol. 32 (10) (2016) 987–995, https://doi. org/10.1016/j.jmst.2016.08.011. [7] P. Mirja, H. Jenny, S. Jaakko, Y. Jouko, S. Niklas, 3D printed drug delivery devices: perspectives and technical challenges, Expet Rev. Med. Dev. 14 (9) (2017) 685–696, https://doi.org/10.1080/17434440.2017.1363647. [8] N. Labonnote, A. Rønnquist, B. Manum, P. Rüther, Additive construction: state-ofthe-art, challenges and opportunities, Autom. ConStruct. 72 (2016) 347–366, https://doi.org/10.1016/j.autcon.2016.08.026. [9] M. Lille, A. Nurmela, E. Nordlund, M.K. Sini, S. Nesli, Applicability of protein and fiber-rich food materials in extrusion-based 3D printing, J. Food Eng. (2017) 1–8, https://doi.org/10.1016/j.jfoodeng.2017.04.034. [10] ISO/ASTM 52900, Additive Manufacturing, Terminology, 2015. [11] N. Mohan, P. Senthil, S. Vinodh, N. Jayanth, A review on composite materials and process parameters optimisation for the fused deposition modelling process, Virtual Phys. Prototyp. 12 (1) (2017) 47–59, https://doi.org/10.1080/ 17452759.2016.1274490. [12] L. Pyl, K.A. Kalteremidou, D.V. Hemelrijck, Exploration of specimen geometry and tab configuration for tensile testing exploiting the potential of 3D printing freeform shape continuous carbon fibre-reinforced nylon matrix composites, Polym. Test. 71 (2018) 318–328, https://doi.org/10.1016/j.polymertesting.2018.09.022. [13] M. Dawoud, I. Taha, S.J. Ebeid, Mechanical behaviour of ABS: an experimental study using FDM and injection moulding techniques, J. Manuf. Process. 21 (2016) 39–45, https://doi.org/10.1016/j.jmapro.2015.11.002. [14] D. Popescu, A. Zapciu, C. Amza, F. Baciu, R. Marinescu, FDM process parameters influence over the mechanical properties of polymer specimens: a review, Polym. Test. 69 (2018) 157–166, https://doi.org/10.1016/j.polymertesting.2018.05.020. [15] J.K. Jha, A. Narasimhulu, A critical review of process parameters of fused deposition modeling, J. Material Sci. Mech. Eng. 5 (3) (2018) 138–141. http://www.krishisanskriti.org/Publication.html. [16] T.Y. Yao, Z.C. Deng, K. Zhang, S.M. Li, A method to predict the ultimate tensile strength of 3D printing polylactic acid (PLA) materials with different printing orientations, Compos. B Eng. 169 (2019) 393–402, https://doi.org/10.1016/j. compositesb.2019.01.025. [17] Y. Xia, K. Xu, G.J. Zheng, R. Zou, B.J. Li, P. Hu, Investigation on the elasto-plastic constitutive equation of parts fabricated by fused deposition modeling, Rapid Prototyp. J. 25 (3) (2019) 592–601, https://doi.org/10.1108/RPJ-06-2018-0147. [18] T.J. Gordelier, P.R. Thies, L. Turner, L. Johanning, Optimising the FDM additive manufacturing process to achieve maximum tensile strength: a state-of-the-art review, Rapid Prototyp. J. 25 (6) (2019) 953–971, https://doi.org/10.1108/RPJ07-2018-0183.
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Effects of fused deposition modeling process parameters on tensile, dynamic mechanical properties of 3D printed polylactic acid materials Shuheng Wang a, b, Yongbin Ma a, b, Zichen Deng a, b, *, Sen Zhang a, b, Jiaxin Cai a, b a b
School of Mechanics, Civil Engineering and Architecture, Northwestern Polytechnical University, Xi’an, 710072, PR China MIIT Key Laboratory of Dynamics and Control of Complex Systems, Northwestern Polytechnical University, Xi’an, 710072, PR China
A R T I C L E I N F O
A B S T R A C T
Keywords: Fused deposition modeling Process parameters Tensile properties Dynamic mechanical properties
Fused deposition modeling (FDM) is an important process among the available additive manufacturing tech nologies in various industries. Although there exists many works investigating the effects of FDM process pa rameters on the mechanical properties of printed materials, there are still several points need to be studied. One is the effects of process parameters on the dynamic mechanical properties of FDM-printed materials, especially in environments where the temperature often changes. The other is the mechanism by which process parameters affect the mechanical properties of printed materials. Aiming at these two points, uniaxial tensile tests and dynamic mechanical analysis are carried out respectively to characterize the tensile properties and dynamic mechanical properties of FDM-printed PLA materials under different FDM process parameters, namely printing angle, layer thickness, fill rate and nozzle temperature. Based on the experimental results explanations are given for the influence of the FDM process parameters on the mechanical properties of the printed materials.
1. Introduction Compared with conventional processing methods, additive manufacturing (AM) is based on an incremental layer by layer manufacturing, which not only can quickly manufacture lightweight and complex structures [1–3] but also enables printing of multi-materials [4,5]. Therefore, applications of AM technology are emerging in several fields, such as aerospace [6], medicine [7], civil construction [8] and food production [9]. Fused Deposition Modeling (FDM) is an AM process based on extrusion, the material being “selectively dispensed through a nozzle or orifice” [10]. In recent years, FDM has become one of the most popular AM technologies due to its easy of use, low cost, and that it is able to process thermoplastic polymers such as ABS, PLA, PC, PS, Nylon and PET [11,12]. However, since the FDM-printed materials are deposited layer by layer, the interlayer bonding is weak, resulting in poor me chanical properties compared with injection molded [13]. There are many process parameters that can be set in the FDM process, which will affect the mechanical properties of the final product. Therefore, it is necessary to have a deeper understanding of the FDM process in order to improve the mechanical properties of the printed material by setting reasonable process parameters.
A relatively large amount of work has been done to investigate the effects of process parameters on the mechanical properties of the FDMprinted materials under static loading [14–19]. Popescu et al. [14] reviewed the effects of different FDM process parameters on different mechanical properties such as tensile, compressive and flexural strength of materials and concluded that the key parameter influencing FDM parts’ mechanical properties are: raster-to-raster air gap, raster angle, layer thickness, infill density and build orientation. In the meantime, Popescu et al. [14] also emphasized that some process such as nozzle and bed temperature were insufficiently studied and the variability in the mechanical properties noted by many authors should be analyzed more deeply and explained in further research work. Jha and Nar asimhulu [15] mentioned that other mechanical properties such as creep and vibration need to be studied. The transversely isotropic elastic model and the Hill anisotropic yield model were used by Yao et al. [16] and Xia et al. [17] to describe the tensile mechanical properties of FDM materials, mainly considering the influence of printing angle. In the work of Gordelier et al. [18], tensile strength can be maximized by improving various process parameters, but the research on printing temperature is insufficient. Researchers’ interests are focused on opti mizing process parameters and establishing theoretical models, and very little work has been done to understand the mechanics of the effects of
* Corresponding author. School of Mechanics, Civil Engineering and Architecture, Northwestern Polytechnical University, Xi’an, 710072, PR China. E-mail address: [email protected] (Z. Deng). https://doi.org/10.1016/j.polymertesting.2020.106483 Received 21 January 2020; Received in revised form 7 March 2020; Accepted 7 March 2020 Available online 10 March 2020 0142-9418/© 2020 Elsevier Ltd. All rights reserved.
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process parameters on mechanical properties. In addition, most litera tures only study the effect of FDM process parameters on the mechanical properties of materials under static loading and ignore the fact that FDM-printed materials may exhibit viscoelastic properties when the materials undergo cyclic deformation under dynamic loading condi tions. In applications such as the automotive industry, most FDM-printed materials are subject to dynamic stress, deformation, and vibration, which can make parts prone to failure, especially at higher temperatures [20]. Therefore, it is necessary to analyze the dynamic mechanical properties of FDM-printed materials. At present, related research focuses on the effects of FDM processes and reinforcing filler on the dynamic properties of FDM-printed mate rials. Based on I-optimal response surface methodology and Q-optimal design, Mohamed et al. [20,21] optimized the dynamic mechanical properties of FDM-printed PC-ABS materials under different FDM pro cesses (layer thickness, air gap, raster angle, build orientation, road width and number of contours). Mansour et al. [22] and Coppola et al. [23] respectively used graphene and clay as reinforcing filler to study their effects on the dynamic mechanical properties of FDM-printed PLA materials. Coppola et al. also studied the effect of nozzle temperature (185-200-215 � C for PLA 4032D and 165-180-195 � C for PLA 2003D) on the dynamic mechanical properties of FDM-printed PLA materials. Taguchi approach was used by Miquel et al. [24] to investigate the in fluence of nozzle diameter on the dynamic mechanical properties of FDM-printed PC materials under different temperatures and frequencies. However, in the above studies, attention was not focused on the mechanism by which the FDM process affects the printed material’s dynamic mechanical properties and process parameters such as tem perature and nozzle diameter often change only two to three times, which sometimes misses some important phenomena. Therefore, it is important to understand how the process parameters affect the static and dynamic mechanical properties of materials. In this paper, four FDM process parameters, namely printing angle, layer thickness, fill rate and nozzle temperature, are selected and reasonably set to better understand the effects of FDM process param eters on the mechanical properties of FDM-printed PLA materials. Considering that PLA exhibits viscoelastic properties and may undergo cyclic deformation under dynamic loading conditions in practical ap plications, dynamic mechanical analysis (DMA) and uniaxial tensile tests are carried out to characterize the tensile properties and dynamic mechanical properties of the FDM-printed PLA materials. Due to the obvious viscosity characteristics of PLA materials at higher tempera tures, the dynamic mechanical properties of FDM-printed PLA materials at different temperatures are also analyzed.
PolyPlus PLA filament with a diameter of 1.75 mm is supplied by Polymaker Industry (China, Shanghai). PolyPlus PLA has good color performance, does not block the nozzle, and provides very stable performance. 2.2. Uniaxial tensile tests The uniaxial tensile tests are carried out in the AGS-X computercontrolled electronic universal testing machine. According to ISO 527-22012 (International standard, plastics determination of tensile proper ties Part 2: Test conditions for moulding and extrusion plastics), the tensile specimens used in the study are designed and fabricated (Fig. 2). The uniaxial tensile experiment setup is shown in Fig. 3 (a). The tensile speed is 2 mm/min and the temperature keep 23 � C during the whole tensile course. So, the test condition can be confirmed to be quasi-static loading and in normal temperature. The extensometer with gauge length of 50 mm is used here to measure the elastic modulus and elongation at break more conveniently. 2.3. Dynamic mechanical analysis Dynamic mechanical analysis is an indispensable and effective tool for determining the dynamic parameters of polymers and composites under cyclic external forces [25]. Dynamic parameters such as storage modulus E’ , loss modulus E’’ , and loss factor tan δ are temperature dependent and have following relationship: tan δ ¼
3. Results and discussions According to Table 2, for each number, five specimens were prepared for uniaxial tensile tests and three specimens were prepared for DMA tests. There are respectively 94 and 63 sets of experimental data are valid, and the average of the experimental results are listed in Table 2 (Because the dynamic mechanical properties of materials change with temperature, only the maximum values are listed). In order to reflect the effects of process parameters on the tensile properties and the dynamic mechanical properties of the FDM-printed PLA materials more clearly, the data in Table 2 is plotted in Fig. 4 and Fig. 8.
2.1. 3D printing machine and printing materials Raise3D Pro2 Plus 3D printer is used to fabricate the specimens. The specimens are designed with SolidWorks 2014® (Dassault Systems SolidWorks Corp, USA) and exported as stl format into the 3D printer software (ideaMaker v.3.4.2, Raise 3D, China). The nozzle diameter of 0.4 mm is selected, and the main structure and the support structure are printed by the same nozzle. This paper mainly studies the effects of four FDM process parameters, namely printing angle, layer thickness, fill rate and nozzle temperature, on the tensile properties and dynamic me chanical properties of FDM materials. The default FDM process param eters are listed in Table 1. The four parameters studied are set as listed in Table 2. The printing angle is illustrated in Fig. 1.
3.1. Effects of process parameters on tensile properties 3.1.1. Effects of printing angle Printing angle influences the anisotropy of the FDM parts. As show in Fig. 4, printing angle has a great influence on the tensile properties of FDM-printed PLA materials, especially the tensile strength and elonga tion at break. The elastic modulus, tensile strength and elongation at break of the FDM-printed PLA materials increase with the increase of the printing angle. This is because the printing angle directly affects the fracture mode of the FDM-printed PLA materials, that is, the interlayer fracture or the intra-layer fracture. The fracture characteristics of the specimens printed in different angles after the uniaxial tensile tests are shown in Fig. 5 (a). When the printing angle is less than 45� , the failure mode of the specimens is interlayer fracture, and when the printing angle is greater than 45� , the failure mode of the specimens is intra-layer fracture. It is noticeable that when the printing angle is 45� , inter-layer
Table 1 Default FDM process parameters. Bed temperature (� C)
Fill Type
Support fill rate (%)
60
60
Grid
30
(1)
Dynamic mechanical properties of FDM-printed PLA materials are measured in tensile mode using a DMA þ450 (01 dB-Metravib, France). Temp Ramp/Freq Sweep test in Multifrequency Strain method is used for dynamic mechanical tests. Tests are carried out under the tempera ture range from 30 � C to 90 � C with a heating rate of 3 � C/min and amplitude of 20 μm at a fixed frequency of 1 Hz in nitrogen atmosphere. DMA experiment set up is shown in Fig. 3 (b). Storage modulus, loss modulus and loss factor are recorded as a function of temperature.
2. Materials and methods
Printing speed (mm/s)
E’’ E’
2
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Table 2 FDM process parameters settings and experimental results. Number
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
FDM process parameter
Average of effective experimental results
Printing angle (� )
Layer thickness (mm)
Fill rate (%)
Nozzle temperature (� C)
Elastic modulus (MPa)
Tensile strength (MPa)
Elongation at break (%)
Storage modulus (MPa)
Loss modulus (MPa)
Loss factor
0 15 30 45 60 75 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90
0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.05 0.15 0.20 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10
100 100 100 100 100 100 100 100 100 100 20 40 60 80 100 100 100 100 100 100 100
210 210 210 210 210 210 210 210 210 210 210 210 210 210 195 200 205 215 220 225 230
2257.98 2287.97 2304.84 2377.18 2389.54 2407.83 2422.63 2460.85 2402.13 2367.90 1459.06 1507.83 1692.26 2005.71 2248.00 2332.67 2359.56 2464.26 2443.75 2431.77 2424.96
27.48 30.69 32.35 37.42 43.93 49.85 53.66 53.70 51.75 50.52 20.04 21.08 23.81 28.50 46.97 47.30 49.18 54.39 54.17 54.27 53.03
1.35 1.47 1.57 2.27 4.39 4.91 5.36 6.28 5.20 4.81 3.50 3.84 4.56 4.66 3.96 4.40 5.02 5.30 4.76 3.10 2.64
2913.51 3132.21 3174.30 3183.19 3216.27 3268.91 3344.07 3377.32 3202.52 3042.90 2408.89 2811.45 2852.44 3000.11 3275.12 3325.09 3314.92 3445.20 3254.61 3259.21 3250.33
501.20 531.12 525.31 549.22 525.89 517.06 525.01 537.34 518.23 512.09 402.11 450.78 465.31 511.18 512.43 521.68 517.24 569.34 554.15 551.09 530.03
2.96 2.98 3.01 3.06 3.01 2.93 2.94 3.02 2.90 2.86 2.78 2.85 2.90 2.92 2.80 2.88 2.88 3.24 3.08 3.02 2.98
The greater the layer thickness, the greater the distance between the nozzle and the deposited material during extrusion, resulting in less pressure between them. Therefore, an increase in the layer thickness causes a decrease in the mass of the deposited material of the same height and an increase in the interlayer air gaps, thereby reducing the interlayer bonding strength of the FDM-printed PLA materials [26]. Similarly, the bonding strength between the extruded filaments is also reduced. In addition, when the printing speed is constant, the increase of the layer thickness will reduce the cooling time of the material and affect the adhesion between the layers, which will further reduce the tensile properties of the printed materials. Since the layer thickness mainly affects the interlayer bonding strength of the printed material, it can be inferred that the smaller the printing angle, the greater the printed material’s tensile strength is affected by the layer thickness. In order to prove this, the tensile strength of standard test specimens with different printing angles at a layer thickness of 0.2 mm was additionally tested. The fracture characteristics of the specimens are shown in Fig. 5 (b), and the comparison of the tensile strength of printed PLA materials with different printing directions at a layer thickness of 0.1 mm and 0.2 mm is shown in Fig. 6. Different from Fig. 5 (a), obviously inter-layer fracture can be observed in Fig. 5 (b) when the printing angle is 45� , which may indicate that inter-layer failure is more likely to occur under tensile load when the layer thickness increases.
Fig. 1. Schematic diagram of printing angle.
fracture and intra-layer fracture occur simultaneously. The interlayer fracture strength depends mainly on the interlayer bonding strength, and the intra-layer fracture depends mainly on the strength of the extruded material. It is apparent that the interlayer bonding strength of the FDM-printed PLA materials is lower than the PLA’s strength. 3.1.2. Effects of layer thickness Layer thickness is a feature parameter in FDM process, which not only has a great influence on the printing time, but also greatly in fluences the precision and mechanical properties of the FDM-printed materials. As shown in Fig. 4, the elastic modulus, tensile strength and elongation at break decrease with the increase of the layer thickness.
3.1.3. Effects of fill rate Fill rate determines the effective cross-sectional area in the tensile direction and interlayer bonding strength of the FDM-printed materials, thus influencing the mechanical properties of the printed materials. As the fill rate increases, the air gaps in the material decrease and the
Fig. 2. The dimension of FDM-printed specimens for uniaxial tensile test. 3
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Fig. 3. (a) Uniaxial tensile experiment set up, (b) DMA experiment set up.
effective cross-sectional area increases [27]. Therefore, it can be seen from Fig. 4 that the elastic modulus, tensile strength, and elongation at break greatly increase as the fill rate increases.
the relaxation of polymer chains, because in polymers, the tendency of energy storage decreases with increasing temperature, and the tendency of loss of energy increases with increasing temperature [30]. For the loss modulus, when temperature rises from 30 � C to 55 � C, it first decreases slowly and then slowly rises. The loss modulus increases quickly when temperature exceeds 55 � C and reaches the maximum at around 59.7 � C after nearly two order of increase. Then the loss modulus decreases quickly by nearly three orders of magnitude. After the tem perature exceeds 67 � C, the loss modulus decreases slower and slower. The tendency of the loss factor to change with temperature is very similar to the loss modulus, only the values are different. When tem perature rises from 30 � C to 57 � C, the loss factor first decreases slowly and then slowly rises. The loss modulus increases quickly when tem perature exceeds 57 � C and reaches the maximum at around 64 � C after two order of increase. When the temperature rises to 80 � C, the loss factor decreases by an order of magnitude and then the decrease speed becomes slower and slower.
3.1.4. Effects of nozzle temperature Nozzle temperature mainly affects the fluidity of extruded material. When the nozzle temperature is too low, due to the poor fluidity of the extruded material, it cannot adhere well to the deposited material, which often leads to unsuccessful printing. When the nozzle temperature is too high, the extruded PLA material is almost liquid or even partially thermally degraded [28,29]. Since the printing speed is unchanged, the previous layer of material has not completely solidified, and the next layer of material starts to print, which will affect the printing accuracy and affect the mechanical properties of the material [26]. As shown in Fig. 4, when the nozzle temperature is raised from 195 � C to 210 � C, the elastic modulus, tensile strength and elongation at break of the printed material increase as the fluidity and bonding strength of the extruded material increase. When the nozzle temperature is raised from 210 � C to 230 � C, the elastic modulus and tensile strength of the material decrease slightly, and the elongation at break decreases rapidly. This may be because the fluidity of the extruded material is too large to guarantee the surface quality of the material and thereby reduce the elongation at break of the material. At the same time, thermal degradation of the PLA material due to higher nozzle temperatures also reduces the mechanical properties of the material. Therefore, by setting the nozzle temperature to 210 � C–215 � C, the mechanical properties of the FDM-printed mate rial will be better.
3.2.1. Effects of printing angle It can be seen from Fig. 8 that the printing angle has a relatively large influence on the dynamic properties of the FDM-printed PLA materials. In general, the storage modulus trends to increase as the printing angle increases. The maximum and minimum values of the storage modulus correspond to printing in the horizontal direction and printing in the vertical direction, respectively. However, the loss modulus and the loss factor first increase and then decrease as the printing angle increases, and reach a maximum in the 45� direction. Similar phenomenon can be seen from previous work [20,31]. Therefore, when subjected to dynamic loading, PLA materials printed in 90� may have more store load po tential, and PLA material printed in 45� may have more potential to dissipate energy rather than storing it.
3.2. Effects of process parameters on dynamic mechanical properties Taking the number 7 experimental data as an example, the measured storage modulus, loss modulus and loss factor are plotted as a function of temperature is shown in Fig. 7. Based on the experimental data, the dynamic mechanical properties of the FDM-printed PLA materials have following characteristics when the temperature rises from 30 � C to 90 � C. The storage modulus decreases with increasing temperature. When temperature rises from 30 � C to 55 � C, the storage modulus decreases slowly (approximately by 7%). However, when the temperature exceeds 55 � C, the storage modulus begins to decrease dramatically. Up to 63 � C, the storage modulus decreased by three orders of magnitude, with the fastest decrease speed at around 59.7 � C. After the temperature exceeds 63 � C, the storage modulus decreases slower and slower. This is due to
3.2.2. Effects of layer thickness Layer thickness also has significant influence on the dynamic me chanical properties of the FDM-printed PLA materials. It can be seen from Fig. 8 that the storage modulus, loss modulus, and loss factor of the FDM-printed PLA materials decrease with increasing layer thickness. This result is consistent with the published study [31]. As mentioned earlier, the smaller the layer thickness, the greater the bonding strength between layers and filaments, resulting in greater stiffness. In the pro cess of dynamic cyclic loading, the smaller layer thickness may have greater constraints on the movement of adjacent polymer chains in PLA, and the loss modulus and loss factor may also be larger. 4
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Fig. 4. Effects of FDM process parameters on (a) elastic modulus, (b) tensile strength, and (c) elongation at break.
3.2.3. Effects of fill rate It is shown in Fig. 8 that as the fill rate increases, the storage modulus and loss modulus of FDM-printed PLA materials increase rapidly, and the loss factor increases relatively slowly. This observation is consistent with the pervious study [20,21,23]. The possible explanation is that with the increase of the fill rate, the air gaps in the material decrease rapidly, which makes the material layers and the filaments more tightly bonded, and the PLA molecular segment movement resistance increases. This not only increases the storage modulus of the printed material, but also increases its loss modulus and loss factor.
especially the loss factor of the material. The storage modulus, loss modulus and loss factor of the material first increase and then decrease with the increase of the nozzle temperature, and reach the maximum at about 215 � C. Compared with the effect of nozzle temperature on the elastic modulus and tensile strength, the dynamic mechanical properties of the FDM-printed PLA materials decrease significantly when the temperature exceeds 215 � C. In previous study [23], the nozzle tem perature was set relatively low (185-200-215 � C for PLA 4032D and 165-180-195 � C for PLA 2003D), so it was only concluded that the dy namic mechanical properties of the FDM-printed material increased as the nozzle temperature increased. Therefore, it can be speculated that when the nozzle temperature is high, the thermal degradation of the PLA material may have a greater influence on the dynamic mechanical properties.
3.2.4. Effects of nozzle temperature Similar to the effect on tensile properties, the nozzle temperature has a greater impact on the dynamic mechanical properties of the material, 5
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Fig. 5. Fracture characteristics of the specimens.
4. Conclusions In this paper, it is found through experiments that the FDM process parameters will affect the mass of the printed material, the interlayer bonding strength, air gaps, etc., and these are the main reasons leading to the different mechanical properties of the printed material. Printing angle mainly affects the fracture mode of the FDM-printed PLA mate rials. When the printing angle is less than 45� , the failure mode of the specimen trends to be interlayer fracture, and conversely, the speci men’s failure mode trends to be intra-layer fracture. Layer thickness mainly affects the interlayer bonding strength of the printed materials. Smaller layer thickness not only strengthen the PLA materials’ interlayer bonding strength, but also may have greater restrictions on the move ment of adjacent polymer chains in PLA materials. The fill rate mainly affects the air gap inside the printed material. With the increase of the fill rate, the air gaps in the material decrease rapidly, which makes the material layers and the filaments more tightly bonded, and increases the resistance of the molecular chain of PLA materials. Nozzle temperature mainly affects the fluidity of extruded material. When the nozzle tem perature is too low, the fluidity of the extruded material is poor, which results in weak interlayer bonding strength. When the nozzle tempera ture is too high, the extruded PLA material is almost liquid, and even partial thermal degradation will occur, which is not conducive to printing.
Fig. 6. Tensile strength of printed PLA materials with different printing di rections at a layer thickness of 0.1 mm and 0.2 mm.
Data availability statement All the raw data required to reproduce these findings have already shown in this paper. Meanwhile, authors declare that their research content and experimental data are true and reliable. Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. CRediT authorship contribution statement Shuheng Wang: Methodology, Validation, Investigation, Writing original draft. Yongbin Ma: Conceptualization, Investigation, Writing -
Fig. 7. Dynamic mechanical properties as functions of temperature. 6
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Fig. 8. Effects of FDM process parameters on (a) storage modulus, (b) loss modulus, and (c) loss factor.
review & editing. Zichen Deng: Conceptualization, Investigation, Writing - review & editing, Funding acquisition. Sen Zhang: Data curation, Investigation. Jiaxin Cai: Data curation, Investigation.
References [1] B.G. Compton, J.A. Lewis, 3D-Printing of lightweight cellular composites, Adv. Mater. 26 (34) (2014) 5930–5935, https://doi.org/10.1002/adma.201401804. [2] J. Souza, A. Großmann, C. Mittelstedt, Micromechanical analysis of the effective properties of lattice structures in additive manufacturing, Addit. Manuf. 23 (2018) 53–69, https://doi.org/10.1016/j.addma.2018.07.007. [3] S.H. Wang, Y.B. Ma, Z.C. Deng, K. Zhang, S. Dai, Implementation of an elastoplastic constitutive model for 3D-printed materials fabricated by stereolithography, Addit. Manuf. (2020), https://doi.org/10.1016/j.addma.2020.101104. [4] M.A. Skylar-Scott, J. Mueller, C.W. Visser, J.A. Lewis, Voxelated soft matter via multimaterial multinozzle 3D printing, Nature 575 (2019) 330–348, https://doi. org/10.1038/s41586-019-1736-8. [5] W.F. Hao, Y. Liu, H. Zhou, H.S. Chen, D.N. Fang, Preparation and characterization of 3D printed continuous carbon fiber reinforced thermosetting composites, Polym. Test. 65 (2018) 29–34, https://doi.org/10.1016/j.polymertesting.2017.11.004.
Acknowledgements This work was supported by the National Key R&D Program of China (2017YFB1102801), the National Natural Science Foundation of China (grant numbers: 11602021), the Natural Science Basic Research Plan in Shaanxi Province of China (grant number: 2019JM-220), and Innova tion Foundation for Doctor Dissertation of Northwestern Polytechnical University.
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S. Wang et al.
Polymer Testing 86 (2020) 106483 [19] L. Wang, D.J. Gardner, Effect of fused layer modeling (FLM) processing parameters on impact strength of cellular polypropylene, Polymer 113 (2017) 74–80, https:// doi.org/10.1016/j.polymer.2017.02.055. [20] O.A. Mohamed, S.H. Masood, J.L. Bhowmik, Characterization and dynamic mechanical analysis of PC-ABS material processed by fused deposition modelling: an investigation through I-optimal response surface methodology, Measurement 107 (2017) 128–141, https://doi.org/10.1016/j.measurement.2017.05.019. [21] O.A. Mohamed, S.H. Masood, J.L. Bhowmik, Mathematical modeling and FDM process parameters optimization using response surface methodology based on Qoptimal design, Appl. Math. Model. 40 (2016) 10052–10073, https://doi.org/ 10.1016/j.apm.2016.06.055. [22] M. Mansour, K. Tsongas, D. Tzetzis, Measurement of the mechanical and dynamic properties of 3D printed polylactic acid reinforced with graphene, Polym. Plast. Technol. Eng. (2018) 1–11, https://doi.org/10.1080/03602559.2018.1542730. [23] B. Coppola, N. Cappetti, L.D. Maio, P. Scarfato, L. Incarnato, 3D printing of PLA/ clay nanocomposites: influence of printing temperature on printed samples properties, Materials 11 (10) (2018), https://doi.org/10.3390/ma11101947, 1947. [24] M. Domingo-Espin, S. Borros, N. Agullo, A.A. Garcia-Granada, G. Reyes, Influence of building parameters on the dynamic mechanical properties of polycarbonate fused deposition modeling parts, 3D Print. Addit. Manuf. 1 (2) (2014) 70–77, https://doi.org/10.1089/3dp.2013.0007. [25] N. Saba, M. Jawaid, O.Y. Alothman, M.T. Paridah, A review on dynamic mechanical properties of natural fibre reinforced polymer composites, Construct. Build. Mater. 106 (2016) 149–159, https://doi.org/10.1016/j. conbuildmat.2015.12.075. [26] X.Y. Tian, T.F. Liu, C.C. Yang, Q.R. Wang, D.C. Li, Interface and performance of 3D printed continuous carbon fiber reinforced PLA composites, Compos. Appl. Sci. Manuf. 88 (2016) 198–205, https://doi.org/10.1016/j.compositesa.2016.05.032. [27] K.L. Alvarez, R.F. Lagos, M. Aizpun, Investigating the influence of infill percentage on the mechanical properties of fused deposition modelled ABS parts, Ing. Invest. 36 (3) (2016) 110–116. [28] G.L. Re, S. Benali, Y. Habibi, J.M. Raquez, P. Dubois, Stereocomplexed PLA nanocomposites: from in situ polymerization to materials properties, Eur. Polym. J. 54 (2014) 138–150, https://doi.org/10.1016/j.eurpolymj.2014.03.004. [29] L.T. Sin, A.R. Rahmat, W.A.W.A. Rahman, Thermal Properties of Poly (Lactic Acid). Polylactic Acid: PLA Biopolymer Technology and Applications. Book Series: PDL Handbook Series, 2013, pp. 109–141. [30] M. Rubinstein, R.H. Colby, Polymer Physics, Oxford University Press, 2003. [31] O.A. Mohamed, S.H. Masood, J.L. Bhowmik, Analytical modelling and optimization of the temperature-dependent dynamic mechanical properties of fused deposition fabricated parts made of PC-ABS, Materials 9 (11) (2016) 895, https://doi.org/10.3390/ma11101947.
[6] L.E. Murr, Frontiers of 3D printing/additive manufacturing: from human organs to aircraft fabrication, J. Mater. Sci. Technol. 32 (10) (2016) 987–995, https://doi. org/10.1016/j.jmst.2016.08.011. [7] P. Mirja, H. Jenny, S. Jaakko, Y. Jouko, S. Niklas, 3D printed drug delivery devices: perspectives and technical challenges, Expet Rev. Med. Dev. 14 (9) (2017) 685–696, https://doi.org/10.1080/17434440.2017.1363647. [8] N. Labonnote, A. Rønnquist, B. Manum, P. Rüther, Additive construction: state-ofthe-art, challenges and opportunities, Autom. ConStruct. 72 (2016) 347–366, https://doi.org/10.1016/j.autcon.2016.08.026. [9] M. Lille, A. Nurmela, E. Nordlund, M.K. Sini, S. Nesli, Applicability of protein and fiber-rich food materials in extrusion-based 3D printing, J. Food Eng. (2017) 1–8, https://doi.org/10.1016/j.jfoodeng.2017.04.034. [10] ISO/ASTM 52900, Additive Manufacturing, Terminology, 2015. [11] N. Mohan, P. Senthil, S. Vinodh, N. Jayanth, A review on composite materials and process parameters optimisation for the fused deposition modelling process, Virtual Phys. Prototyp. 12 (1) (2017) 47–59, https://doi.org/10.1080/ 17452759.2016.1274490. [12] L. Pyl, K.A. Kalteremidou, D.V. Hemelrijck, Exploration of specimen geometry and tab configuration for tensile testing exploiting the potential of 3D printing freeform shape continuous carbon fibre-reinforced nylon matrix composites, Polym. Test. 71 (2018) 318–328, https://doi.org/10.1016/j.polymertesting.2018.09.022. [13] M. Dawoud, I. Taha, S.J. Ebeid, Mechanical behaviour of ABS: an experimental study using FDM and injection moulding techniques, J. Manuf. Process. 21 (2016) 39–45, https://doi.org/10.1016/j.jmapro.2015.11.002. [14] D. Popescu, A. Zapciu, C. Amza, F. Baciu, R. Marinescu, FDM process parameters influence over the mechanical properties of polymer specimens: a review, Polym. Test. 69 (2018) 157–166, https://doi.org/10.1016/j.polymertesting.2018.05.020. [15] J.K. Jha, A. Narasimhulu, A critical review of process parameters of fused deposition modeling, J. Material Sci. Mech. Eng. 5 (3) (2018) 138–141. http://www.krishisanskriti.org/Publication.html. [16] T.Y. Yao, Z.C. Deng, K. Zhang, S.M. Li, A method to predict the ultimate tensile strength of 3D printing polylactic acid (PLA) materials with different printing orientations, Compos. B Eng. 169 (2019) 393–402, https://doi.org/10.1016/j. compositesb.2019.01.025. [17] Y. Xia, K. Xu, G.J. Zheng, R. Zou, B.J. Li, P. Hu, Investigation on the elasto-plastic constitutive equation of parts fabricated by fused deposition modeling, Rapid Prototyp. J. 25 (3) (2019) 592–601, https://doi.org/10.1108/RPJ-06-2018-0147. [18] T.J. Gordelier, P.R. Thies, L. Turner, L. Johanning, Optimising the FDM additive manufacturing process to achieve maximum tensile strength: a state-of-the-art review, Rapid Prototyp. J. 25 (6) (2019) 953–971, https://doi.org/10.1108/RPJ07-2018-0183.
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