Date of Award

2010

Publisher

North Dakota State University

Document Type

Thesis

Degree Awarded

Doctor of Philosophy (PhD)

Program

Mechanical Engineering

Department

Mechanical Engineering

College

Engineering

Faculty Advisor

Ulven, Chad A.

Description

Incorporating reinforcement within a polymer (i.e. composite) can obtain substantial performance increases. However, composites may he susceptible to conditions that could have a significant impact on their performance. The objective of this study was to characterize SpaceAge Synthetics (SAS) fiberglass-reinforced rigid, closed-cell polyurethane foam (PU) after subjected to various environmental conditions. SAS composites were characterized as a function of material composition after conditioned to extreme temperatures, moisture, ultraviolet irradiation (UV), or a combination thereof. The experimental process involved accelerated conditioning to further induce property changes and assure long-term integrity. Empirical expressions for SAS composites were generated to represent performance changes for different environmental conditions. Increasing temperature 93 °C from ambient showed an 18% decrease in strength and 24% decrease in stiffness for a 450 kg/m3 foam density reinforced with 7.6% fiber volume fraction. This performance loss resulted from the ductility of the polymer increasing with temperature. Decreasing temperature 68 °C from ambient showed a 56% increase in strength and 26% increase in stiffness. When SAS composites were subjected to moisture at room temperature, no statistical difference was observed after being exposed to l 00% RH for 72 h duration. These mechanical performance analyses included varying material parameters such as: foam density, fiber content, void content, and thickness. The addition of heat to the l 00% RH moisture drastically reduced mechanical performance up to 33% in strength and 22% in stiffness. Ultraviolet irradiation caused chemical changes within the SAS composites, which was first noted by the pronounced color shift within the yellowness index (YI). Additional reinforcement near the surface created a 269% lower shift in YI. It was observed that initially cross-linking occurred while at the same time chain scission was occurring at a larger rate. Fourier Transform Infrared Spectroscopy proved that UV penetrated 0.25 mm within the surface, showing the effects occur mainly on the surface. Finally, SAS composites exhibited a 31 % increase in strength and a 12% increase in stiffness with a post cure process. Post curing for 4 h at 100 °C raised the glass transition temperature from 119 °C to 128 °C. The performance increase was attributed from the post cure process inducing additional cross-linking within polymer chains.

Rights

NDSU policy 190.6.2

Rights Link

https://www.ndsu.edu/fileadmin/policy/190.pdf

Handle Identifier

https://hdl.handle.net/10365/33738

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