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Improving Strength and Fracture Resistance in Fused Filament Fabrication Through Printhead-Integrated In-Situ Annealing

Ph.D. in Mechanical Engineering · The University of Texas at Arlington · Summer 2026 Advisor: Dr. Robert M. Taylor · Defended 14 August 2026

View in the UTA MavMatrix repository

Problem

Fused filament fabrication builds parts layer by layer, and polymer healing across each interlayer weld is usually incomplete. The result is anisotropic behaviour: parts are strong along the print direction and weak across it.

Post-process annealing can strengthen those interfaces, but heating the whole part risks dimensional distortion and warpage. On thin geometries that trade is rarely acceptable.

Approach

This work reheats each layer locally as it is deposited, using a heated annular plate integrated into the printhead. Softening the incoming filament would destroy the back pressure that drives extrusion, so the design pairs the heating element with upstream cooling that keeps the feed rigid.

The studies cover neat ABS and short-carbon-fiber ABS (ABS-CF), combining non-isothermal healing theory with in-process measurement. Bonding potential, welding time, and critical bonding temperature link the measured thermal history to interfacial healing.

Methods

• In-process infrared thermography for interfacial thermal history and welding time above the glass transition
• X-ray micro-computed tomography for void morphology and volume fraction
• SEM fractography to identify whether failure ran along the interface or through the polymer
• Tensile testing, DMA, and Mode-I fracture testing to ASTM D5528 (DCB) and ASTM D5045 (SENB)
• Full-factorial design of experiments analysed with GLM/ANOVA and Tukey HSD

Results

Neat ABS, batch printing. A full-factorial study established a practical operating window for localized annealing and produced an average 48.5% increase in build-direction toughness, rising to 68% under the best condition of low speed and close spacing.

ABS-CF. Higher interfacial thermal exposure gave a 39% increase in tensile strength, 63% in glassy storage modulus, and 92% in Mode-I fracture resistance. Scatter fell as well: the coefficient of variation in fracture toughness dropped from 20.1% to 9.5%, because annealing closed the large voids sitting on the load path rather than densifying the part uniformly.

Adaptive printhead. With independent control of plate temperature and standoff, plate temperature dominated within the process window. The best condition raised tensile strength by 34% and toughness by 58%. A thin-wall box beam gained 55% in flexural strength.

Fracture. DCB conditional propagation resistance rose 84.3% and SENB total work 96.2%, while elastic stiffness stayed largely unchanged. The benefit therefore sits in the interlayer damage and fracture process, not in bulk stiffening.

Conclusion

Controlling local thermal history during printing improves interlayer healing, reduces critical mesostructural defects, and raises strength and fracture resistance, without the dimensional risk of whole-part annealing.

One limit is worth stating. Performance does not rise without bound as heat input increases. The useful window is set jointly by material, geometry, print speed, plate temperature, and standoff, and thermal exposure is a property of the process and geometry together rather than of the setting alone.

Outputs

Journal articles · conference papers · patents