Micromechanical behavior of short-fiber polymer composites

Micro-Raman Spectroscopy (MRS) has been used to measure the load transfer in short-fiber, high-modulus/epoxy composites as a function of angle to the loading direction, and to monitor strain concentrations in short-fiber composites due to fiber/fiber interactions. Toray M40B PAN-based carbon fibers were tested with sized, unsized, elastomer-treated surfaces. The matrix was Shell Epon 828 cured with TETA. It was found that incremental load transfer to the fibers compared well with theory. It was also found that the maximum strain transfer rate did not depend on the angle of orientation. The interface was found to change the strain concentration factors, with a noticeable decrease in the strain concentration factors observed for a weaker, more brittle interface. The strain concentration results were used to modify an existing model of composite strength.