INTERFACIAL EVALUATION OF CARBON FRINFORCED NANO-COMPOSITES USING ELECTRICAL RESISTANCE MEASUREMENT WITH WETTING TESTS

The use of carbon fiber reinforced plastic (CFRP) is rapidly increasing in aerospace and automobile applications. This is in large part due to the increase strength and modulus of carbon fiber composites compared to other materials such as glass fiber composites. The fiber-matrix interface has been found to be important for high strength in composites. Methods that have been studied and developed to improve interfacial property of composites include: the addition of coupling agents, surface modifications, chemical reaction control and use of nano-fillers for reinforcement. During mechanical loading the shape of carbon fibers, in a composite, is altered with a concomitant change in electrical resistance. Carbon fibers are used as sensing elements in CFRP due to their electrical conductivity. In some more advanced studies, in CRFP, the carbon fibers were used for both strain sensing and damage sensing. The basic theory, in such studies, was that the movement of carbon fiber could be detected by electrical resistance measurement. During loading, the extent of contact between carbon fibers in a CF tow is altered, and the electrical resistance changes from its initial value. In this work, interfacial properties of carbon fiber/polymer composites were evaluated by such electrical resistance measurements. During the wetting process of CF tows by the polymer resins, the change in electrical resistance was recorded and analyzed. The test results for different carbon fibers and polymer resins exhibited different trends. The electrical resistance change was associated with the different wetting conditions, and the interfacial properties were predicted by these electrical resistance measurements. CF tow/epoxy exhibited the poorest carbon tow wettability, the smallest change in resistance and the poorest IFSS and ILSS. For the four systems studied, the relative change in each of these quantities for the materials of a given composite was roughly proportional to the other measured quantities. This may have some very significant practical importance. It may point the way to use quick easy tests to screen and predict other behaviors for composites of different materials and/or processes. Perhaps a simple resistance change test might be used to predict and select good candidate materials, surface processing techniques for high strength composite applications. The proportional relationship between interfacial adhesion and electrical resistance change was obtained by trend fitting line analyses. Ultimately, it was demonstrated that mechanical properties related to interfacial properties might potentially be predicted by electrical resistance measurement and studies of wetting behavior, using empirical formulas and correlations.