Direct Ink Writing of Functional Fiber/Granular Composites

Author

• Zhuoyuan Yang, Embry-Riddle Aeronautical UniversityFollow

ORCID Number

0009-0006-2521-6432

Date of Award

Summer 2026

Access Type

Dissertation - Open Access

Degree Name

Doctor of Philosophy in Aerospace Engineering

Department

Aerospace Engineering

Committee Chair

Yizhou Jiang

Committee Chair Email

jiangy5@erau.edu

First Committee Member

Daewon Kim

First Committee Member Email

kimd3c@erau.edu

Second Committee Member

Sirish Namilae

Second Committee Member Email

namilaes@erau.edu

Third Committee Member

Thomas Yang

Third Committee Member Email

yang482@erau.edu

College Dean

James W. Gregory

Abstract

Direct ink writing provides a versatile manufacturing route for fabricating functional fiber and granular composites with controlled architecture, tunable interfaces, and customized material distributions. Fiber reinforced composites offer high stiffness, strength, fatigue resistance, and functional anisotropy, while granular composites provide scalable access to particle based structures with high material efficiency and broad resource compatibility. However, the additive manufacturing of these composite systems remains challenging. For fiber based composites, precise control of fiber placement, matrix impregnation, interfacial bonding, and freestanding deposition is difficult to achieve during printing. For granular composites, stable particle flow, controllable packing, binder infiltration, and shape retention are strongly affected by particle interactions and process conditions. These challenges limit the fabrication of structurally reliable and geometrically complex composite materials.

This dissertation focuses on the direct ink writing of functional fiber and granular composites through integrated material design, process control, and structural optimization. A series of printing strategies were developed to address key limitations in composite additive manufacturing. Coaxial direct writing was used to integrate continuous fibers with polymer matrices and to regulate the local fiber matrix interface. Interfacial modulation was introduced to improve bonding between fibers and surrounding materials. Multi material printing further enabled the deposition of chopped fibers and functional fillers across different matrix systems and length scales. These approaches allowed the local architecture, mechanical response, and functional properties of fiber reinforced composites to be tailored during fabrication.

To further expand the geometric capability of continuous fiber thermoset composites, an in situ heat tracing mechanism was developed for freestanding 3D printing. Electric current was applied through the carbon fiber during deposition, generating localized Joule heating to cure the surrounding thermoset matrix in real time. This approach enabled rapid and localized curing, improved interfacial bonding, reduced the dependence on post curing, and allowed the fabrication of support free composite structures. By coupling fiber delivery, thermal control, and thermoset curing within a coaxial printing process, this method provides a pathway for manufacturing continuous fiber composites with complex three dimensional geometries and enhanced structural integrity.

In parallel, vibration assisted direct writing was developed for granular composite printing. Controlled vibration was used to regulate particle flow, deposition stability, and packing behavior during extrusion. Subsequent binder infiltration enabled the formation of particle reinforced composite structures with improved shape retention and mechanical robustness. This strategy extends direct ink writing from fiber based systems to granular materials and provides a potential route for resource efficient composite manufacturing using particle based feedstocks.

Together, these studies establish a direct ink writing platform for functional fiber and granular composites. The developed strategies improve material compatibility, interfacial control, structural fidelity, and freestanding fabrication capability across different composite systems. This work advances composite additive manufacturing from simple material deposition toward controlled fabrication of architected, multifunctional, and mechanically reliable structures.

Scholarly Commons Citation

Yang, Zhuoyuan, "Direct Ink Writing of Functional Fiber/Granular Composites" (2026). Doctoral Dissertations and Master's Theses. 1001.
https://commons.erau.edu/edt/1001