Carbon Fiber and Syntactic Foam Hybrid Materials via Core–Shell Material Extrusion Additive Manufacturing

Abstract

alone, [4] thereby enabling significantly higher bending stiffness and buckling resistance in the natural hybrid architecture, and enabling optimal structural and functional performance to the organism at minimal metabolic cost. Additive manufacturing, which offers novel capabilities absent in traditional manufacturing, [7] enables fabrication of bioinspired architectures such as the C-S motif described above. In particular, direct ink writing (DIW), a type of material extrusion additive manufacturing, allows precise patterning of viscoelastic feedstock materials at ambient temperatures to build structural and/or functional components in a layer-by-layer fashion. [8] A wide variety of feedstock inks have been formulated for DIW, allowing fabrication of a broad range of materials including polymers, [9-12] ceramics, [13-15] metals, [16-18] and composites. For example, epoxy-based composite feedstocks reinforced with silicon carbide whiskers, [19-21] nanoclay, [9] graphene, [12] and carbon fibers (CFs) [11,22-24] have been explored recently to improve strength and stiffness in printed materials. Further mechanical improvement can be realized by applying the C-S architecture to high stiffness CF inks coupled with low-density foam inks for the shell and core materials, respectively. Here, we report for the first time a new C-S printhead (Figure 1b) specifically designed to print highly loaded, fiberfilled inks, as well as a new low-density syntactic epoxy foam ink for use as a low-density core material in hybrid C-S architectures. Composite-foam C-S architectures exhibit up to 25% higher specific flexural stiffness (E 1/3 /ρ) than either of the constituents alone, while the printable foam is ≈40% less dense than the existing printed polymers with comparable mechanical properties. Implementation of the C-S architecture via DIW has been investigated for both functional and structural applications with polymers and other material systems. For example, Moon et al. fabricated hollow-core ceramics by extruding a fugitive camphene core surrounded by a camphene/alumina shell, followed by sintering to densify the alumina framework. [25] Fu et al. printed carbon core-alumina shell filaments in a truss structure utilizing a piston-driven co-extrusion unit with alumina-and carbon-filled aqueous colloidal gels. [26] For lightweight hierarchical ceramic architectures, Muth et al. printed hollow C-S struts using an aqueous particle-stabilized foam Biological materials often employ hybrid architectures, such as the core-shell (C-S) motif present in porcupine quills and plant stems, to achieve unique specific properties and performance. Drawing inspiration from these natural materials, a new method to fabricate lightweight and stiff C-S architected filaments is reported. Specifically, a C-S printhead conducive to printing highly loaded fiber-filled inks, as well as a new low-density syntactic foam ink, are utilized to 3D-print C-S architectures consisting of a syntactic epoxy foam core surrounded by a stiff carbon fiber-reinforced ep...

Recent Advances in Multi-Material 3D Printing of Functional Ceramic Devices

“…This strategy makes it possible to fabricate functionally graded patterns with tunable properties (e.g., strength, coefficient of thermal expansion, and permittivity). The third strategy uses a multicore-shell nozzle with several specific inputs connected to corresponding syringes, which enables the coextrusion of multiple inks to form a core-shell filament ( Figure 7 f–g) [ 137 , 138 ].…”

3D-printing of ceramic filaments with ductile metallic cores

“…Polymer lattices combining high stiffness and toughness have been printed using core-shell filaments with co-extrusion systems that required specially designed printing heads with concentric cylinders. [15,16] Co-extrusion has also been used to build optical waveguides, [17] biopolymers [18], polymer composites, [19] fiber based supercapacitors with organic binders [20] or shape memory polymers containing metallic fibers [21,22]. In the latter case, the long metallic fibers are co-extruded as a wire inside the polymer shell.…”

Size effects in 3D‐printed polymer‐derived, zirconium diboride‐reinforced ceramic composites

“…13 While these studies are promising, light-based methods limit the type and amount of filler that can be included in an AM feedstock because the resins must remain spreadable in uniform, thin layers, and the depth of cure must remain large enough that entire layers can be cured. 8,13 Conversely, material extrusion AM requires specific rheological properties for the feedstock that can be achieved through the use of high loading of filler materials 5,14,15 and fillers that strongly influence the rheology of the resin. 10,16,17 For example, Pack et al created printable syntactic epoxy foams loaded with up to 58 vol.% spherical glass microballoons, 14 while Kemp et al created inks based on PSZ and PSC for material extrusion AM that contained 40 vol.% hexagonal boron nitride (hBN) 15 and 47.5 vol.% zirconium diboride (ZrB 2 ), 5 respectively.…”

“…8,13 Conversely, material extrusion AM requires specific rheological properties for the feedstock that can be achieved through the use of high loading of filler materials 5,14,15 and fillers that strongly influence the rheology of the resin. 10,16,17 For example, Pack et al created printable syntactic epoxy foams loaded with up to 58 vol.% spherical glass microballoons, 14 while Kemp et al created inks based on PSZ and PSC for material extrusion AM that contained 40 vol.% hexagonal boron nitride (hBN) 15 and 47.5 vol.% zirconium diboride (ZrB 2 ), 5 respectively. In these studies, linear shrinkage associated with pyrolysis was reduced to ∼7% for the hBN-filled composite and less than 5% for the ZrB 2 composite.…”

“…While these studies are promising, light‐based methods limit the type and amount of filler that can be included in an AM feedstock because the resins must remain spreadable in uniform, thin layers, and the depth of cure must remain large enough that entire layers can be cured 8,13 . Conversely, material extrusion AM requires specific rheological properties for the feedstock that can be achieved through the use of high loading of filler materials 5,14,15 and fillers that strongly influence the rheology of the resin 10,16,17 . For example, Pack et al.…”