Compression Characterization of High-modulus Carbon Fibers

Abstract

The study deals with testing and modeling the mesoscopic compression behavior of high-modulus carbon fibers-reinforced epoxy. These fibers are very stiff, but their compression performances are poor. To decrease the risk margins during the sizing process, it is necessary to determine their compression behavior as accurately as possible. Two tests were carried out on two types of high-modulus carbon fibers (M55J fibers and K63712 fibers): the pure compression Celanese test, which gives poor strain results, and a new pure bending test, which allows large displacements and generates higher strain levels. This bending test makes it possible to know without inverse calculation the load for any sections and to use machine specimens in order to avoid tab effects. An elastic nonlinear model (a power function of the strain) is proposed to describe the loss of compressive rigidity until the brittle rupture. Model coefficients are identified for the two materials with a simple inverse calculation. The pure bending test brought to light a highly nonlinear behavior of the unidirectional K63712 fibers.