| Abstract Scope |
Direct ink writing (DIW) technology facilitates layer-by-layer deposition of customized viscoelastic composite ink through controlled extrusion via a fine nozzle at reduced pressure, enabling the creation of 3D objects with minimal labor and tooling requirements. A primary challenge in DIW, particularly for thermoset composites, is to formulate a printable ink with suitable rheological attributes, including apparent viscosity, yield stress, and viscoelastic properties, such as storage and loss modulus, for achieving high shape fidelity in fabricated structures.
In this context, a high-performance advanced material system was employed to develop a printable composite ink comprising of short carbon fiber, epoxy matrix, and other rheology modifiers for DIW of composite structures with honeycomb truss core. We were successful in incorporating a high carbon fiber (~40 wt.%) through innovative processing technology, which allows the printing of a 10-layer (~3.25 mm) unsupported truss structure using a 0.58-mm nozzle. Rheological assessments of the ink indicated pronounced shear thinning behavior, ensuring ink flow through the nozzle even at lower extrusion pressures. Upon the removal of applied stress outside the nozzle, the material reverted to a viscoelastic solid, demonstrating shape fidelity, a critical parameter assessed by the ratio of loss modulus (G″) to storage modulus (G′). The resulting honeycomb structures, fabricated using the ink, exactly mimic the digital 3D model, showcasing high print quality. Quasi-static compression tests demonstrated reported specific strength and stiffness, measuring at 33.830 ± 4.445 Pa. m3/Kg and 0.701 ± 0.031 KPa. m3/Kg, respectively, suggesting their suitability for use as cores in sandwich structures. |