Mechanical & Materials Engineering, Department of


Date of this Version



A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Mechanical Engineering and Applied Mechanics, Under the Supervision of Professor Mehrdad Negahban. Lincoln, Nebraska: May, 2015

Copyright (c) 2015 Evan S Schwahn


In an effort to construct materially graded parts, a strategy was studied that is based on varying ratios of interpenetrating polymer networks (IPNs) in a manner that can be adapted to 3D printing. Using IPNs has the benefit of allowing access to a broad range of property variation. The strategy used involves controlled partial curing of the first network, followed by washing of that network to remove uncured components, then swelling of the structure with a second polymer component and curing.

This method was utilized to control final IPN properties by controlling the extent of crosslinking of the initial network, a strategy that can be adapted in 3D printing by controlled curing with a laser system. Controlled continuous graded property distribution could eliminate the need for fasteners and other costly manufacturing steps, and could provide designers with a tool to specify property distribution to obtain functionally graded parts that have property distributions that are optimized for an application. A 3D printer based on the stereolithography rapid prototyping concept has been developed to implement this strategy.

The system studied for property graded 3D printing was an acrylate/epoxy system. The curing of the acrylate component, Bisphenol A ethoxylate dimethacrylate, was studied by rapid-scan FTIR and modeled for adaptation in 3D printing. Many parameters affect the crosslinking process of the acrylate. These include the power density profile of the laser beam, exposure time, exposure overlap, power density, and curing environment (temperature and oxygen content). These effects were investigated and analyzed for implementation in a model that was used for its adaptation to 3D printing.

The epoxy component was 3,4-Epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate, and was photo cured after swelling inside the partially cured acrylate network. The properties of the final pseudo IPN structures were characterized by nanoindentation. Initial parts made by this method indicated a gradual variation of elastic properties.

Advisor: Mehrdad Negahban