(Dr. Jon Colton, advisor)
"Material Systems for Rapid Manufacture of Composite Parts"
A manufacturing process is proposed that builds complex composite parts using a layered building process in which each layer of pre-preg composite material is laid and cured as the build progresses. In order to employ on-line curing without molds, new resin technologies that provide fast curing at room temperature are investigated. Both ultraviolet curable resins and epoxy/polyamide combinations that cure quickly at low temperatures are studied.
UV curable resins that use a cationic driving mechanism are tested for their ability to "shadow" cure. Composites made with carbon fiber are exposed to ultraviolet light to determine if the cure propagates from areas directly exposed to UV energy to areas under fibers directly exposed. A low temperature curing epoxy/polyamide mixture is tested for the effects of cure temperature, cure time, and mix ratio on the final degree of cure (%DOC) and glass transition temperature, Tg. Layers are made using different resin mixtures, partially cured or prestaged, and used to build layered parts to determine curing characteristics during the lay-up process.
Though ultraviolet curing showed advantages in cure time and low
volatile production, very minimal "shadow" curing is achieved. This
limits on-line curing to parts using glass fibers and compromises the flexibility
of the process. In the epoxy/polyamide mixtures, mix ratio is shown
to have little effect on the reaction rate but did have an effect
on the Tg. The rate of Tg increase and the ultimate attainable Tg
increased with increasing mix ratio to 50 parts polyamide to 100 parts
epoxy. For mix ratios above 50 parts per hundred, mix ratio had no
effect on Tg. A kinetic model is established for the resin epoxy/polyamide
system for optimizing processing conditions during fabrication. During
the build process, the degree of cure in each layer increased significantly
over the prestaged degree of cure. However, the final resin properties,
such as Tg, are still below the specifications for high performance parts.
New resin technology development is recommended that combines fast curing
properties with necessary higher final properties.