Research

1. 3D Printing of Continuous Fiber-Reinforced Polymer Composites

3D printing enables mold-free fabrication of continuous fiber-reinforced polymer (CFRP) composites with enhanced design flexibility and reduced manufacturing costs, making it ideal for rapid product development. Our research focuses on developing new 3D printing technologies for CFRPs to overcome the material and processing limitations of current methods.

Notably, we have developed a novel direct-ink-writing printhead capable of processing a wide range of thermally curable and UV-curable resins, as well as commercial continuous fibers such as carbon, Kevlar, and glass. The process also supports functional resins for printing reprocessable and recyclable CFRPs. By integrating a six-axis robotic arm with customized path-planning algorithms, we enable conformal printing with spatially controlled fiber placement. In addition, we have introduced an embedded 3D printing technique that allows dynamic control over fiber volume fractions and matrix composition during printing. Together, these innovations expand the design space and manufacturing capabilities for next-generation high-performance, multifunctional CFRPs with broad applications in aerospace, automotive, and renewable energy sectors.

The development of these printing techniques is supported by process modeling frameworks that capture the mechanics of the printing process, the resulting material properties, and functional performance. By incorporating machine learning, these models enable rapid prediction of material–process–property relationships and facilitate the optimization of fiber architecture, composite topology, and manufacturing parameters 

2. 4D Printing

Our research is focused on developing novel shape-changing polymers and composites, and integrating them into existing or newly developed printing processes to fabricate morphing structures, actuators, and active metamaterials. For example, we recently formulated a new liquid crystal elastomer (LCE) resin compatible with vat photopolymerization-based 3D printing to create intricate, free-standing structures with reversible actuation capabilities. This material platform advances a wide range of 4D printing applications, including morphing structures, soft robotics, and active metamaterials (left figure), which expands the design space for programmable shape-changing systems.

In another effort, we developed a 4D printing method based on direct ink writing to fabricate monodomain LCE composites reinforced with continuous fibers (right figure). Beyond their traditional role in mechanical reinforcement, continuous fibers offer new opportunities for tailoring the actuation behaviors of 4D printed structures. For instance, during printing, fibers can be strategically positioned in locations where it collaborates synergistically with the actuation abilities of matrix materials, thereby achieving unprecedented mechanical properties and multifunctionality.

3. Mechanics of Energy-Dissipative Liquid Crystal Elastomers

We are broadly interested in the mechanics of energy-dissipative materials and structures designed to protect against dynamic impacts and mechanical insults. Liquid crystal elastomers (LCEs) are of particular interest due to their remarkable energy dissipation behavior and high fracture toughness. In addition to conventional viscoelastic relaxation, LCEs exhibit mesogen rotation under mechanical loading, which provides an additional mechanism for energy dissipation.

Our research focuses on developing mechanics constitutive theories that link microscale mesogen organization and rotation to macroscale material behavior. This understanding has been extended into computational simulations and guides the design and 3D printing of LCE-based structural components (bottom left) and protective layers (bottom right) for safeguarding fragile and valuable assets in defense and biomedical applications.

4. Sustainable Manufacturing and Recycling of Engineering Composites 

Our group is committed to advancing sustainable manufacturing and recycling of engineering composites by developing new materials and processing strategies that leverage dynamic covalent chemistry, particularly bond exchange reactions (BERs). As a notable example, we have established a primary recycling method for epoxy composites using a low-toxicity organic solvent. Upon immersion, small solvent molecules diffuse into the polymer network, cleave the polymer chains via transesterification BERs, and ultimately depolymerize the matrix material. Clean fibers can be recovered without damage. The depolymerized resin can serve either as a valuable standalone product or be reused to fabricate new composites with near-identical mechanical properties. This process involves only mild heating and is simple, cost-effective, and easy to implement. It offers a sustainable alternative to conventional disposal methods such as landfilling, incineration, and chemical degradation.

We have extended this recycling approach to support sustainable manufacturing and recyclable 3D printing of various engineering plastics and composites. In parallel, we have developed a series of chemomechanics-based constitutive theories and computational models to describe the evolution of network structure and properties under different material and recycling conditions. These insights guide the rational design of polymer systems and process parameters for improved sustainability and performance.