Date of Award

Summer 8-16-2024

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Civil Engineering

Advisor

Roberto A. Lopez-Anido

Second Committee Member

Keith A. Berube

Third Committee Member

Sunil Bhandari

Abstract

The research evaluates the longevity of large-format 3D printed polymer composite parts for infrastructure applications, particularly concerning the effects of water immersion and freeze-thaw cycling. Two petroleum-based polymer composite materials– Carbon fiber reinforced acrylonitrile butadiene styrene (CF-ABS) and glass fiber reinforced polyethylene terephthalate glycol (GF-PETG), and one bio-based polymer composite material– Wood f iber reinforced amorphous polylactic acid (WF-aPLA) were selected for this study. The longevity was assessed by characterizing the physical, thermal, and mechanical properties of 3D-printed thermoplastic composites. The 3D-printed specimens were subjected to accelerated aging conditions following ASTM standards. Baseline mechanical properties were evaluated by tension testing a set of unaged specimens. The change in mechanical properties after 30, 60, and 90 days of accelerated water immersion at three different temperatures and after 3, 6, and 9 freeze-thaw cycling were evaluated. Further, mechanical properties after exposure to exterior environmental conditions for 90 days were evaluated. The material properties were evaluated in two directions-along the direction of material deposition and across the layers. Results show significant reductions in mechanical properties, especially in bio-based materials, after 90 days of moisture exposure. Properties across layers were more affected than in the deposition direction. Bio-based polymers saw the most decline, up to 45% in average tensile strength in the through-thickness direction and 41% in average tensile modulus in the longitudinal direction. Minimal changes occurred after 3, 6, and 9 cycles of freeze-thaw exposure. In addition, this thesis summarizes the prediction model for predicting the longevity of 3D-printed thermoplastic composites based on accelerated aging test results. Finally, this thesis provides the material property retention factors to account for different environmental exposures for use in the structural design of 3D-printed thermoplastic composites.

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