Fiber‐filled composite materials offer a unique pathway to enable new functionalities for systems built via extrusion‐based additive manufacturing (or “3D printing”); however, challenges remain in controlling the fiber orientations that govern ultimate performance. In this work, a multi‐material, shape‐changing nozzle—constructed by means of PolyJet 3D printing—is presented that allows for the spatial distribution of short fibers embedded in polymer matrices to be modulated on demand throughout extrusion‐based deposition processes. Specifically, the nozzle comprises flexible bladders that can be inflated pneumatically to alter the geometry of the material extrusion channel from a straight to a converging–diverging configuration, and in turn, the directional orientation of fibers within printed filaments. Experimental results for printing carbon microfiber‐hydrogel composites reveal that increasing the nozzle actuation pressure from 0 to 100 kPa reduced the proportion of aligned fibers, and notably, prompted a transition from anisotropic to isotropic water‐induced swelling properties (i.e., the ratio of transverse to longitudinal swelling strain decreased from 1.73
This content will become publicly available on December 1, 2024
High through-thickness thermal conductivity of 3D-printed composites via rotational direct ink writing
Composites printed using material extrusion additive manufacturing (AM) typically exhibit alignment of high-
aspect-ratio reinforcements parallel to the print direction. This alignment leads to highly anisotropic stiffness,
strength, and transport properties. In many cases, it would be desirable to increase mechanical and transport
properties transverse to the print direction, for example, in 3D-printed heat sinks or heat exchangers where heat
must be moved efficiently between printed roads or layers. Rotational direct ink writing (RDIW), where the
deposition nozzle simultaneously rotates and translates during deposition, provides a method to reorient fibers
transverse to the print direction during the printing process. In the present work, carbon fiber-reinforced epoxy
composites were printed by RDIW with a range of nozzle rotation rates and the in-plane and through-thickness
thermal conductivity was measured. In addition, the orientation of carbon fiber (CF) in the composites was
measured using optical microscopy and image analysis, from which second-order fiber orientation tensors were
calculated. These results showed that the orientation of CF became less anisotropic as nozzle rotation rate
increased, leading to increased through-thickness thermal conductivity, which increased by 40% at the highest
rotation rate. The orientation tensors also showed that RDIW was more effective at reorienting fibers within the
in-plane transverse direction compared to the through-thickness transverse direction. The results presented here
demonstrate that a current weakness of material extrusion AM composites—poor thermal conductivity in the
through-thickness direction—can be significantly improved with RDIW.
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- Award ID(s):
- 1825815
- NSF-PAR ID:
- 10482724
- Publisher / Repository:
- Elsevier B.V.
- Date Published:
- Journal Name:
- Additive Manufacturing Letters
- Volume:
- 7
- Issue:
- C
- ISSN:
- 2772-3690
- Page Range / eLocation ID:
- 100167
- Subject(s) / Keyword(s):
- ["Additive manufacturing","Composites","Thermal conductivity","3D printing","Rotational direct ink writing","Fiber orientation","Epoxy","Carbon fiber"]
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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