3D Printing of Hybrid Architectures via Core-Shell Material Extrusion Additive Manufacturing

Biological materials often employ hybrid architectures, such as the core-shell motif present in porcupine quills and plant stems, to achieve unique properties and performance. Drawing inspiration from these natural materials, a new method to fabricate lightweight and stiff core-shell architected filaments is reported. Specifically, a core-shell printhead conducive to printing highly loaded fiber-filled inks, as well as a new low-density syntactic foam ink, are utilized to 3D-print core-shell architectures consisting of a syntactic epoxy foam core surrounded by a stiff carbon fiber-reinforced epoxy composite shell. Effective printing of test specimens and structures with controlled geometry, composition, and architecture is demonstrated with printed core-shell samples exhibiting up to a 25 percent increase in specific stiffness over constituent materials.

A detrimental increase in foam density was observed during initial core-shell printing due to failure of glass microballoons (GMBs) during extrusion. To solve this, the second part of the dissertation investigates the relationships between GMB loading, extrusion pressure, nozzle diameter, and flowrate on printed density. These parameters are investigated to gain understanding of the conditions leading to GMB failure, informing selection of process parameters to minimize it. A new syntactic foam ink is formulated with GMBs that exhibit a lower average diameter and higher crush strength, ultimately enabling printing without prominent GMB failure and the ability to achieve near theoretical printed density. The new foam samples are stronger and stiffer than conventional syntactic foams and current DIW-printed foams. Further implementation of the new foam in the C-S architecture enabled a 5 percent increase in specific stiffness over previous values.

In the last study, work is done to further expand the capability of C-S printing by demonstrating multimaterial 3D printing using the core-shell nozzle. This approach enables “on-the-fly” switching between materials during fabrication, without the need for two nozzles. Material transition behavior is analyzed, multimaterial components are successfully printed, and flexural testing is conducted. Overall, the new approach enables material switching with a continuous print path, providing greater design flexibility and compositional control, opening new routes to DIW print multimaterial architectures.