Date of Award

Spring 7-23-2015

Document Type

Thesis

Degree Name

Master of Science (MS)

First Advisor

Wilfred V. Srubar

Second Advisor

Petros Sideris

Third Advisor

Yunping Xi

Abstract

The feasibility of manufacturing high-performance, prestressed natural-fiber reinforced biopolymer composites is demonstrated in this work. The objective of this study was to illustrate that the specific mechanical properties of biopolymers, namely polylactic acid (PLA), can be enhanced by leveraging a combination of (a) additive manufacturing (3D printing) and (b) initial post-tensioning of continuous natural fiber reinforcement. In this study, both tensile and flexural PLA specimens of various cross-sectional geometries were 3D-printed with and without post-tensioning ducts. The mechanical properties of two continuous reinforcing fibers, jute and flax, were characterized prior to threading, post-tensioning to a prescribed level of stress, and anchoring using a mechanical loading frame. The effect of fiber type, matrix cross-sectional geometry, number of reinforcing strands, and degree of post-tensioning on the specific mechanical properties (e.g., strength-to-weight, stiffness-to-weight) of PLA were investigated using both tensile and flexural mechanical testing. Finite element models of a subgroup of the composite specimens were developed and the same experimental tests were simulated using the models. Additionally, analytical equations were derived for the prediction of composite tensile mechanical properties. Experimental results confirm that 3D-printed matrices improve the specific tensile and flexural mechanical properties of PLA composites and that these properties are further improved via initial fiber prestressing. The experimental data indicate statistically significant increases (p-value < 0.05) in specific strengths of 116% and 32% and specific stiffnesses of 62% and 29% in tension and flexure, respectively, compared to unreinforced PLA specimens. The results suggest that both additive manufacturing and fiber prestressing represent viable new methods for improving the mechanical performance of natural fiber-reinforced polymeric composites. Finite element model simulation results, as well as results from mechanics-based analytical equations, for mechanical behavior of the composite specimens aligned well with obtained data, thus further strengthening the validity of the experimental results. This study considered only mechanical behavior of natural fiber-reinforced biopolymeric composites; the need remains for future research in other aspects (e.g., long-term durability, economic constraints) in order to further demonstrate the viability of these novel composite materials for construction applications.

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