Proceedings of the ASME 2015 International Manufacturing Science and Engineering Conference MSEC2015 June 8-12, 2015, Charlotte, North Carolina, USA

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1 Proceedings of the ASME International Manufacturing Science and Engineering Conference MSEC June 8-12,, Charlotte, North Carolina, USA MSEC-9436 ADDITIVE MANUFACTURING OF CFRP COMPOSITES USING FUSED DEPOSITION MODELING: EFFECTS OF CARBON FIBER CONTENT AND LENGTH Fuda Ning Department of Industrial Engineering, Texas Tech University Lubbock, Texas, 799, USA Weilong Cong* Department of Industrial Engineering, Texas Tech University Lubbock, Texas, 799, USA Junhua Wei Department of Mechanical Engineering, Texas Tech University Lubbock, Texas, 799, USA Shiren Wang Department of Industrial and Systems Engineering, Texas A&M University College Station, Texas, 77843, USA Meng Zhang Department of Industrial and Manufacturing Systems Engineering Kansas State University Manhattan, Kansas, 6606, USA ABSTRACT Additive manufacturing (AM) technologies have been successfully applied in various applications. Fused deposition modeling (FDM), one of popular AM techniques, is most widely used method for manufacturing of plastic materials. Due to the poor strength properties of pure plastic materials, there is a critical need to improve mechanical properties for FDMfabricated pure plastic parts. One of the possible methods is adding reinforced materials (such as carbon fibers) into plastic materials to form carbon fiber reinforced plastic (CFRP) composites. The investigation in this paper is going to test if the properties of CFRP composites part will be enhanced compared with pure plastic part made by FDM. There are three major steps in this paper including producing thermoplastic matrix CFRP composites filaments extruded after blending plastic pellets and carbon fiber powder, printing parts in FDM process, and conducting tensile test. Effects of carbon fiber content and length on the mechanical properties (tensile strength, Young s modulus, toughness, ductility, and yield strength) of specimens are investigated. This investigation will also provide guidance for future investigations of fabricating thermoset matrix CFRP composites by AM techniques. KEYWORDS Additive manufacturing (AM); Carbon fiber reinforced plastic (CFRP) composites; Fused deposition modeling (FDM); Mechanical properties; Tensile test. *Corresponding author weilong.cong@ttu.edu 1 INTRODUCTION Additive Manufacturing Additive manufacturing (AM) is defined as a process of joining materials to make objects from 3D model data, usually layer upon layer, as opposed to subtractive manufacturing methodologies [1]. This technique makes it possible to build a large range of durable and functional components with complex geometries that are unable or difficult to be manufactured by conventional methods. Consequently, AM technologies have been successfully applied in various applications in the past three decades, due to its advantages in improvement of materials and process, and advancement of modelling and design [2]. The largest three rapid-increasing areas of AM include aerospace, automotive, and medical instruments and apparatuses [3]. Other areas include product design [4], architecture [], education [6], and fashion [7]. Currently, there are numerous popular AM techniques used in industry beginning with a CAD file of the object to be built, including fused deposition modeling (FDM) [8], selective laser sintering (SLS) [9], selective laser melting (SLM) [], laser engineered net shaping (LENS) [11], direct metal deposition (DMD) [12], stereolithography apparatus (SLA) [13], laminated object manufacturing (LOM) [14], and three-dimensional printing (3DP) []. AM of Plastic Since FDM was first developed in 1989 (Stratasys Inc., 1 Copyright by ASME

2 Eden Prairie, MN, USA) [8], it has been extensively used for manufacturing of plastic materials and it is the only AM technology that can create sparse-fill construction together with soluble support material. However, only thermoplastics are presently used as a feedstock for FDM [16]. The most commonly used thermoplastic material in FDM is ABS (acrylonitrile butadiene styrene), followed by PC (polycarbonate), PLA (polylactide), PPSF (polyphenylsulfone), and mixtures thereof [8]. In FDM, 3D plastic parts can be built layer by layer depositing build material and support material together, both of which are heated and extruded through two extrusion nozzles separately on the liquefier head, as shown in Figure 1. Support material is first deposited onto the foam base to form a foundation for the part, and then the build platform moves downward slightly to make space for the next layer of build material. Each single layer will be deposited repeatedly in the same way on the previous one, being fed by the filament spools of the two types of materials until the part is completed. Finally, support material can be removed by water-based cleaning solution in tank with no surface damages. FDM of plastics are used to make conceptual prototypes with mature development stages [17]. However, the pure thermoplastics built by FDM are lack of strength in producing fully functional and load-bearing parts. These drawbacks restrict the wide applications of FDM technology [18, 19]. Therefore, there is a critical need to develop materials with higher strength and greater functionality to overcome these limitations. One of the possible methods is to add reinforced materials (such as carbon fibers) into plastic materials forming carbon fiber reinforced plastic (CFRP) composites, which could provide better mechanical properties than pure plastics [16, ]. Since in CFRP composites, the carbon fibers are able to support the load. Meanwhile, the polymer matrix is used to bind and protect the fibers and transfer the load to the reinforcing fibers. This paper is going to use FDM technology to fabricate CFRP Liquifier head Extrusion nozzles Part Support Foam base Build platform Support material spool Build Material spool FIGURE 1 SCHEMATIC OF FDM PROCESS composites parts to test if their properties will be enhanced compared with pure plastic part made by FDM. FDM of CFRP Composites Currently, there has been a very limited number of studies on developing new materials especially the fiber reinforced thermoplastic composites for the FDM process. Tekinalp et al. [16] investigated short carbon fiber reinforced ABS composites at different fiber loadings to fabricate composite specimens using FDM. Such specimens showed significant increases in both strength and modulus, and the largest value of these two properties occurred in wt% carbon fiber-loaded FDM samples. Shofner et al. [18] developed nanofiber reinforced ABS composites as an FDM feedstock adding single-walled carbon nanotubes into ABS materials. An average of nearly % increase in tensile strength was obtained at nanofiber loading of wt%. Zhong et al. [19] investigated the application of glass fiber reinforced ABS composites for use as filament in FDM. The results showed that glass fibers could improve the mechanical properties of the filament. Although some attempts have been made to develop new composites to improve the properties of the existing thermoplastics for the FDM process, there are no literatures reporting comprehensive investigations on a wide range of mechanical properties in FDM of CFRP composites parts using American Society for Testing and Materials (ASTM) standardized method [21]. Purpose of the Paper In this study, CFRP composites filaments will be firstly produced during the extrusion by blending carbon fiber powder into the plastic pellets. Then, they will be used for printing CFRP composites parts in FDM process. Finally, tensile test of CFRP composites parts will be carried out to obtain the mechanical properties, including tensile strength, Young s modulus, toughness, ductility, and yield strength. Effects of carbon fiber content and length on these mechanical properties of fabricated parts will be investigated. Correctly selecting the proper content of the carbon fiber in CFRP composites parts with desirable mechanical properties is critical for the success of this work. Successfully accomplishing the investigation of FDM of CFRP composites parts will provide knowledge on the improvement of FDM-printed parts. In addition, no limitations of fabricating thermoplastic matrix CFRP composites parts with any complex shapes will provide guidance for making thermoset matrix CFRP composites components in industry. The remainder of this paper is organized as follows: Section 2 will present experimental conditions. Section 3 will provide and discuss experimental results. Conclusions will be drawn in Section 4. 2 EXPERIMENTAL CONDITIONS 2 Copyright by ASME

3 Experimental Set-up The whole fabrication process of CFRP composites is shown in Figure 2. ABS plastic pellets were purchased. Carbon fiber powder used in this paper (Panex, Zoltek Companies Inc., St. Louis, MO, USA) had two different average lengths of 0 µm and 0 µm with the same average diameter of 6 µm. The pellets and carbon fiber powders were mixed in a blender with different carbon fiber weight percentages including 3 wt%, wt%, 7. wt%, wt%, and wt%. The plastic extruder (EB-1, ExtrusionBot Co. Chandler, AZ, USA) was used to extrude the carbon fiber filled filaments. The FDM 3D printer (AW 3D HD, Airwolf Co., Costa Mesa, CA, USA) was used to fabricate 3D CFRP composites parts. The parameters of these two fabrication processes were summarized in the Table 1. The FDM-fabricated pure plastic TABLE 1 PARAMETERS OF FABRICATION PROCESSES Processes Input variables Value Unit Extrusion temperature 2 C Extrusion Filament yield speed 2 m/min Nozzle diameter 2.8 mm Nozzle temperature 2 C Printing velocity (for the first layer) 1.2 m/min Printing velocity 1. m/min (for rest layers) FDM Nozzle diameter 0. mm Layer number 12 Layer thickness 0.2 mm Deposition direction 4 Infill density 0 % part (white) and CFRP composites part (black) are shown in Figure 3. There are many challenges during the fabrication of the specimens. The diameter of filament is not well controllable and consistent in the process of extrusion as the filament is very difficult to get fed reliably especially after a long time. The uniformity of filament is hard to realize and either narrower or wider filament will result in FDM printing problems. Carbon fiber additives could clog the extruder nozzle since they are viscous and easy to coagulate at a lower temperature. Besides, the output end of the nozzle in FDM process could be blocked as well due to the accumulated dust on the filament, or even actual debris inside the filament. Tensile Test The tensile test was conducted according to ASTM D638- standard. Five specimens were prepared for testing CFRP composites according to the type-і sample, as type-і sample is preferred and should be used when the thickness of specimen (3 mm) is less than 7 mm. Dimensions of the FDM-fabricated part were illustrated in the Figure 4. Other detailed dimensions conforming to type-і sample could be referred in ASTM D638- standard. Tensile tests were conducted in a test machine (AGS-J, Shimadzu Co., Kyoto, Japan) using force transducer with a capacity of kn. The data of force versus strain was collected with help of a data acquisition (Trapezium 2, Shimadzu Co., Kyoto, Japan). The testing speed, sampling frequency, and distance between two grips were set at mm/min, Hz, and 1 mm, respectively. The mechanical properties of CFRP composite parts were determined by testing five specimens at each carbon fiber content. Plastic pellets Blender Second extrusion Extruder Filament Carbon fiber Parts FDM 3D printer FIGURE 2 FABRICATION PROCESS OF CFRP COMPOSITES PARTS 3 Copyright by ASME

4 3 mm± 0.4 mm FIGURE 3 FDM-FABRICATED PARTS R 76mm 13 mm±0.mm 3 EXPERIMENTAL RESULTS 16 mm 19 mm+ 6.4 mm FIGURE 4 DIMENSIONS OF THE FDM-FABRICATED PART A typical strain-stress curve of CFRP composites specimens with five different carbon fiber contents is illustrated in Figure. The average carbon fiber length is 0 µm. Among all the five specimens within each particular carbon fiber content (for example, 3 wt%), the curve was selected from the specimen who had the maximum number of values that were the most closed to the mean value of each mechanical properties. The following mechanical properties can be obtained from strain-stress curves: tensile strength, Young s modulus, toughness, ductility, and yield strength. Effects of Carbon Fiber Content Effects of carbon fiber content on mechanical properties (including tensile strength, Young s modulus, toughness, ductility, and yield strength) of CFRP composites specimen are shown in Figure 6. Boxplots were used to describe the trend with the distribution of data at each carbon fiber content. It can be seen from Figure 6 (a) that, with increasing of Stress (MPa) wt% 2 3 wt% 3 wt% 4 7. wt% wt% 6 wt% Strain (%) FIGURE THE STRAIN-STRESS CURVE OF THE SPECIMENS WITH DIFFERENT CARBON FIBER CONTENTS carbon fiber content, tensile strength firstly increased and then decreased at the settings of carbon fiber content from wt% to wt%. Especially when the carbon fiber content increased from 7. wt% to wt%, a sharp reduction of tensile strength occured, followed by a rise from wt% to wt%. The largest tensile strength value (42 MPa) could be found at carbon fiber content of wt%, while the smallest value was 34 MPa (almost the same with that of pure ABS plastics) when carbon fiber content was wt%. Effect on Young s modulus is shown in Figure 6 (b). After an increase of Young s modulus with increasing of carbon fiber content from 0 wt% to 7. wt%, there was a decrease when the carbon fiber content increased from 7. wt% to wt%. Continuing increasing carbon fiber content to wt%, Young s modulus increased again. Young modulus was the largest (2 MPa) at carbon fiber content of 7. wt% while the smallest value (19 MPa) was found in pure plastic specimen. It can be observed from Figures 6 (c) and (e) that both toughness and yield strength had an overall decreasing tendency when carbon fiber content increased from 0 wt% to wt% (except for a gentle rise at carbon fiber content of wt%). When carbon fiber content exceeded wt%, these two mechanical properties increased again. The largest values for both toughness and yield strength could be found in pure plastic specimen. CFRP specimen with wt% carbon fiber content generated the smallest values of toughness and yield strength (0.63 J*m -3 * 4 and 18.7 MPa, respectively). Effect on ductility is shown in Figure 6 (d). It can be observed that the ductility decreased with increasing of carbon fiber content from 0 wt% to wt%. Then, the ductility increased when carbon fiber content exceeded wt%. The pure plastic specimen had the largest ductility of 4.14 %. Adding wt% carbon fiber content into the plastic led to the smallest ductility of 2.74 % Copyright by ASME

5 0 Tensile strength (MPa) 4 2 Young's modulus (MPa) (a) Tensile strength (b) Young s modulus Toughness (J*m -3 * 4 ) Ductility (%) (c) Toughness 1 (d) Ductility Yield strength (MPa) 2 (e) Yield strength FIGURE 6 THE EFFECT OF CARBON FIBER CONTENT ON MECHANICAL PROPERTIES OF CFRP COMPOSITES SPECIMENS Copyright by ASME

6 Effects of Carbon Fiber Length A comparison of the strain-stress curves of CFRP composites parts between two carbon fiber lengths (0 µm and 0 µm) at carbon fiber content of wt% is shown in Figure 7 (a) that had the same principle with Figure for choosing the curves. In Figure 7 (a), among all the five specimens within each particular carbon fiber length (for example, 0 µm), the curve was selected from the specimen who had the maximum number of values that were most closed to the mean value of each mechanical properties. As strain increased, the part with carbon fiber length of 0 µm first reached the maximum tensile stress. Figure 7 (b) illustrates comparisons of each mechanical Stress (MPa) Tensile strength (MPa) 0 µm 0 µm Strain (%) (a) Strain-stress curves Young's modulus (MPa) Toughness (J*m -3 * 4 ) (b) Mechanical properties Ductility (%) 0 µm 0 µm Yield strength (MPa) FIGURE 7 THE COMPARISONS BETWEEN SPECIMENS WITH CARBON FIBER LENGTH OF 0 μm AND 0 μm AT CARBON FIBER CONTENT OF WT% property between the two types of specimens. Error bar covers from the maximum value to the minimum value. It can be seen that CFRP composites specimen with 0 µm carbon fiber had larger tensile strength and Young s modulus than that with 0 µm carbon fiber. Compared with CFRP composites specimen with 0 µm carbon fiber, specimen with 0 µm carbon fiber had smaller toughness and ductility, respectively. A paired sample t-test has been conducted to compare the yield strength between these two kinds of specimens. Null hypothesis is that there is no significant difference in yield strength between specimens with carbon fiber length of 0 µm and that of 0 µm. The associated P-value (0.891) in the t-test indicates that the null hypothesis cannot be rejected at the common statistical level of 0.0. That means the difference of yield strength between the two specimens is not statistically significant. 4 CONCLUSIONS In this study, effects of carbon fiber content and length on mechanical properties (tensile strength, Young s modulus, toughness, ductility, and yield strength) of specimens were investigated. The following conclusions were drawn from this study. (1) Compared with pure plastic specimen, adding carbon fiber to plastic materials could increase tensile strength and Young s modulus, however, toughness, ductility, and yield strength were decreased. (2) Specimen with carbon fiber content of wt% had the largest tensile strength and specimen with carbon fiber content of 7. wt% had the largest Young modulus. Adding carbon fiber content to wt% or 7. wt% could increase tensile strength and Young s modulus with an increase of 22.% and.%, respectively. (3) CFRP composites specimen with 0 µm carbon fiber had larger tensile strength and Young s modulus than that with 0 µm carbon fiber. Compared with CFRP composites specimen with 0 µm carbon fiber, specimen with 0 µm carbon fiber had smaller toughness and ductility. The yield strengths of these two kinds of specimen are nearly the same. REFERENCES [1] ASTM F a, 12, Standard Terminology for Additive Manufacturing Technologies, ASTM International, West Conshohocken, PA, USA. [2] Sugavaneswaran, M., and Arumaikkannu, G., 14, Modelling for Randomly Oriented Multi-material Additive Manufacturing Component and its Fabrication, Materials & Design, 4, pp [3] Online, Additive Manufacturing: Opportunities and Constraints, 13, Royal Academy of Engineering, available at: Eng_Roundtable_Document.pdf 6 Copyright by ASME

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