Date Available

4-28-2023

Year of Publication

2023

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Engineering

Department/School/Program

Mechanical Engineering

First Advisor

Dr. Y.Charles Lu

Abstract

Literature has shown that 3D printed composites may have highly anisotropic mechanical properties due to variation in microstructure as a result of filament deposition process. Laminate composite theory, which is already used for composite products, has been proposed as an effective method for quantifying these mechanical characteristics. Starting with the analysis of comparing the printing orientation of premanufactured carbon fiber reinforced filament, the mechanical properties of 3D printed objects were examined. The mechanical properties changed not only as a result of machine choice, but how the sample is oriented along the printing bed. The analysis continued with looking at the dynamic properties of 3D printed composites. Results showed that the direction of the extruded strands altered the modal frequencies even for a sample with the same geometry. With the direction of the extruded strands affecting the mechanical properties, the composition of these strands is also shown to affect the mechanical properties of 3D printed composites. For commercially available fiber reinforced filaments, it was found through microscopic analysis that the fiber content stated by the manufacturer is inaccurate. In order to apply Classical Laminate Composite Theory (CLCT) the fiber volume fraction and aspect ratio need to be known. This lead to the creation of custom filament with the desired fiber content and geometry. The Halpin-Tsai model was used to predict the mechanical behavior of short fiber reinforced composites. Finally, the mechanical properties of continuous fiber composites were examined. The continuous fiber samples showed that fiber orientation had an vast effect on mechanical properties. A well oriented composite notably outperformed other fiber orientations with a drastic drop in Young's modulus even with slight misalignment in fiber direction, but also resulted in brittle responses which may not be preferable. CLCT is applied using the simulation software ansys workbench. The results showed considerable correlation for each orientation and can be an accurate predictor of mechanical characteristics for 3D printed continuous fiber composites.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2023.277

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