Effects of surface plasma treatments, elastomeric interphase layers and rubber tougheners on carbon-fiber/epoxy composite properties: Preparation, finite element modeling, mechanical testing and NDE

he effects of introducing a thin, fiber/matrix elastomeric interphase and rubber tougheners to continuous carbon fiber/epoxy matrix composites were studied. PAN-based carbon fibers were pretreated with oxygen plasmas (50W, 3 min.). Composites were made including several with elastomeric polyurethane interphase fiber coatings and/or CTBN rubber tougheners. Composite moduli, determined by NDE and DMTA, decreased as the thickness of the elastomeric layer or the amount of rubber tougheners increased. The interlaminar shear strength (ILSS) increased 34% while the iMPact strength (IS) decreased 49% upon replacing as-received carbon fibers with the oxygen plasma-treated (50W, 3 min.) fibers. Introducing interphases of 700, 1000, and 1400A thickness onto the plasma-treated fibers increased the IS from 111 to 197, 210, and 203 J/m, respectively. Rubber-toughened epoxy matrix composites also exhibited enhanced IS (range of 183-198 J/m). Bimodal or trimodal particle distributions were observed in the rubber-toughened epoxy systems by transmission electron microscope studies. A 3-D finite element model was created to analyze the deformations and stress distributions within unidirectional continuous carbon fiber composites with thin elastomeric interphase coatings on the fibers and a rubber-toughened epoxy matrix containing two different sizes (0.64 and 2.2...