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

In studying shear stresses that develop in the matrix as a consequence of microbuckling of fibres in a unidimensional composite it has been shown that the fibre 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 fibres fail under local compression on their concave side before failing in local tension, and that such a compression fibre failure crierion 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 fibre/epoxy systems.