Date of Award

Summer 8-18-2023

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Civil Engineering

Advisor

Roberto Lopez-Anido

Second Committee Member

Eric Landis

Third Committee Member

Jose Colon Quintana

Abstract

In large-format extrusion-based additive manufacturing of polymer composites, the relationship between material properties and processing parameters requires further investigation. This thesis focuses on the relationship between fiber orientation and thermomechanical properties for short fiber-filled thermoplastic polymer systems manufactured by extrusion-based additive manufacturing. Fiber orientation is particularly important in determining the thermomechanical properties of the composite material as properties in the direction of deposition are expected to be higher for highly aligned fibers than randomly aligned fibers. Fiber orientation distribution, which is related to processing parameters and deposition conditions, can be efficiently represented by the orientation tensor. The orientation tensor can be incorporated in micromechanics models of the composite material to predict thermomechanical properties. This thesis implements the orientation tensor in a homogenization process for a short fiber-filled thermoplastic composite material using micromechanics models and attempts to validate the thermomechanical predictions through a set of experiments. The homogenization process serves to characterize the effect of manufacturing and deposition factors. The ratio between the cross-sectional area of the deposited bead and the cross-sectional area of the extrusion nozzle was identified as a key factor impacting the fiber orientation. As this ratio increases, the proportion of fibers aligned in the deposition direction decreases and the proportion of fibers aligned in the transverse direction increases. The proportion of fibers aligned in the through-thickness direction is largely unaffected. These trends in fiber alignment appear in the experimentally determined thermomechanical properties; the bead geometries with the highest fiber alignment in the deposition direction exhibited the greatest storage modulus at 30°C in the same direction, and the storage modulus at 30°C in the through-thickness direction exhibited very little change across all bead geometries. The experimentally obtained fiber orientations were implemented in a homogenization process with two micromechanics models, the Mori-Tanaka model and the Halpin-Tsai model, to examine the utility of homogenization as a rational engineering tool to select material parameters.

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