China: Researchers Test Short Carbon Fiber/PEEK Composites in FDM 3D Printing

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SEM of brittle flexural fractured cross‐section of printed CF/PEEK parts. (a) The shell of printed CF/PEEK parts. (b) The core of printed CF/PEEK parts. (c), (d) The enlarged figures of (a), (b), respectively (red circles and blue arrows mean carbon fibers and direction of printing filaments, respectively).

Chinese researchers are investigating the power of short carbon fibers combined with PEEK, in relation to FDM 3D printing, a method popular with users due to its power, affordability, and speed. Outlining their findings in “Flexural Properties and Fracture Behavior of CF/PEEK in Orthogonal Building Orientation by FDM: Microstructure and Mechanism,” authors Qiushi Li, Wei Zhao, Yongxiang Li, Weiwei Yang, and Gong Wang test this composite for possible use in a growing number of industrial applications.

PEEK is finding emerging uses in industrial FDM 3D printing, and is known to produce parts with good strength and heat resistance that go on to offer high performance for applications like aerospace and the medical field. Layer adhesion, however, is a common problem in 3D printing, and FDM with PEEK is no exception. The researchers point out that rapid crystallization is another problem leading to poor integrity in prints. While the use of PEEK offers great benefit, it is not able to stand up to the quality of conventional injection molding techniques, leaving researchers to experiment with a variety of ways to bolster its strength and performance.

Carbon is becoming widely used for industrial 3D printing purposes due to its enormous ability to enhance mechanical properties and strength overall; still, however, in the past there have been issues with increased porosity and layer adhesion. The authors examined a way to combine short composite carbon fibers and PEEK with greater success, printing it within the orthogonal building orientation, and continuing to compare it to the quality of parts made through injection molding.

The samples were created on a Funmat HT FDM 3D printer, a machine specifically created for high-temperature FDM 3D printing. Models were designed in Catia V5, and imported via INTAMSUITE. The authors reported that all samples were fabricated with the same printing parameters in both horizontal and vertical orthogonal orientations. Filament was also made into pellets and then subjected to injection conditions for comparison. The results showed that composites tested through both 3D printing and injection molding had ‘similar high strength and toughness.’

“With the addition of CFs, the horizontally printed CF/PEEK composites exhibited a 7.1% lower value of than that of PEEK, which agrees with a previous report on the addition of carbon nanotubes (CNTs),” reported the authors. “Surprisingly, the vertically printed PEEK and CF/PEEK composites displayed a value of 146 MPa, which was similar to the value of the molded samples. Such a similar value between printed samples and molded samples is rare, but quite highly desired, for 3D printing.

“… the incorporation of CF resulted in an 8.30% higher modulus for the CF/PEEK molded samples relative to those of the PEEK samples. A statistically significant increase in the modulus was also observed for the vertically printed samples.”

Flexural properties of printed and molding (M) polyether ether ketone (PEEK) and carbon fiber (CF)/PEEK specimens. (a) CF/PEEK bending specimens with orthogonal printing direction (horizontal and vertical) both printed according to ISO 178:2010 (size: 80 × 10 × 4 mm3). (b) Typical stress to strain curves of flexural experiments. The inset in the bottom right corner shows the linear range that determines the module of each bending specimen. The boxplots of (c) bending strength and (d) bending modulus of flexural specimens, which indicate the distribution of experimental data.

With the addition of SCFs to the PEEK material, the researchers noted increased porosity, and four fracture modes were noted in bending tests with large strain.

“The design of a printing route along the stress orientation that cooperates with the incorporation of a reinforced phase into the matrix provides an effective method to enhance the mechanical properties of composites and enlarges the application of 3D printing in lightweight design fields,” concluded the researchers. “This study will be helpful to designers to investigate the influence of microstructures on printed composites during the printing process.”

Differential scanning calorimetry (DSC) results of printed PEEK and CF/PEEK parts. (a) The position of DSC testing samples. (b) Heat flow curves of CF/PEEK and PEEK parts. (c) Otherness of crystallinity of shell and core of printed PEEK parts. (d) Corresponding crystallinity results of printed CF/PEEK parts.

The vast new world of materials emerging offers countless combinations of different plastics and metals and more, opening the potential for so many applications within so many different fields. Today we see composites like those made from clay, injectable hydrogels, different types of electrical composites, and so much more. Also, find out more about CF/PEEK here. What do you think of this news? Let us know your thoughts! Join the discussion of this and other 3D printing topics at 3DPrintBoard.com.

The major mode of deformation during bending. (a) The deformation mode of the vertically printed specimens. (b) The deformation mode of horizontally printed specimens.

[Source / Images: Flexural Properties and Fracture Behavior of CF/PEEK in Orthogonal Building Orientation by FDM: Microstructure and Mechanism]
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