ORCID Identifier(s)

0009-0006-8243-5690

Graduation Semester and Year

Summer 2026

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Mechanical Engineering

Department

Mechanical and Aerospace Engineering

First Advisor

Dr. Robert M Taylor

Abstract

Fused filament fabrication (FFF) provides substantial design flexibility for thermoplastic and fiber-reinforced components, but the layer-by-layer deposition process creates anisotropic mechanical behavior because polymer healing across interlayer welds is often incomplete. Conventional post-process annealing can strengthen these interfaces, but heating the entire part can lead to dimensional distortion and warpage. This dissertation develops and evaluates a printhead-integrated in situ annealing approach for acrylonitrile butadiene styrene (ABS) and short carbon fiber reinforced ABS (ABS CF), using a heated annular plate to locally reheat recently deposited material during printing.

The research combines nonisothermal polymer healing concepts with in-process infrared thermography, X-ray micro-computed tomography, mechanical testing, dynamic mechanical analysis, fracture testing, and fractography. Bonding potential, welding time, and critical bonding temperature are used to relate the measured thermal history to interfacial healing. A full factorial batch printing study on neat ABS established a practical operating window for localized annealing and produced an average 48.5 percent increase in build direction toughness. The approach was then extended to ABS CF, where the annealed condition showed higher interfacial thermal exposure together with a 39% increase in tensile strength, a 63% increase in glassy storage modulus, and a 92% increase in Mode I fracture resistance. The coefficient of variation in fracture toughness also decreased from 20.1% to 9.5%.

A patent-pending printhead with independent control of annealing plate temperature and standoff distance was subsequently evaluated. Plate temperature was found to be the dominant factor within the investigated process window. Under the best condition, tensile strength increased by 34 percent and toughness by 58%. A thin wall box beam study further showed a 55% increase in flexural strength. The final fracture study evaluated the treated interface using double cantilever beam and single edge notched bend specimens. In situ annealing increased conditional propagation resistance by 84.3 percent in DCB testing and total work by 96.2 percent in SENB testing, while the elastic stiffness remained largely unchanged. This indicates that the primary benefit of the treatment was associated with the interlayer damage and fracture process rather than with bulk elastic stiffening.

Overall, the results demonstrate that controlling the local thermal history during printing can improve interlayer healing, reduce critical mesostructural defects, and increase strength and fracture resistance while avoiding the dimensional risks associated with whole-part post-process annealing. The work establishes a process, structure, and fracture based framework for improving interlayer integrity in FFF thermoplastics and provides a foundation for future adaptive thermal control during additive manufacturing.

Keywords

Fused filament fabrication; In-situ annealing; Interlayer bonding; Mode-I fracture; Micro-computed tomography; ABS and ABS composites

Disciplines

Computer-Aided Engineering and Design | Manufacturing | Structural Materials

License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.

Comments

This is the 3rd revised version of the dissertation submitted on 19th August 2026. The comments from the the library has been addressed on this version.

Download

Available for download on Friday, August 18, 2028

Share

COinS