On the failure criteria for unidirectional carbon fibers composite materials under compression

When studying shear stresses developed in the matrix as a consequence of the microbuckling of fibers in a * it has been shown that the fiber failure criterion based on the tensile stresses on its convex side is not realistic because it gives shear strains in the surrounding matrix which are beyond the ultimate shear strains measured experimentally. In fact, it is shown that fibers fail under local compression on their concave side before failing in local tension, and that such a compression fiber failure criterion is in agreement with experimental data. Furthermore, the present study confirms that the microbuckling half-wavelength is equal to the kink band width for current carbon fiber/epoxy systems.