Kink band formation in fiber reinforced materials

Compressive failure by fiber kinking of unidirectional fiber composites is analysed. Constitutive equations for fiber composites are constructed on the basis of constituent properties. Fiber kinking in the absence of imperfections is predicted as localization of deformation at a bifurcation stress where ellipticity of the incremental equilibrium equations is lost.

A formulation is given which allows the study of post-bifurcation behavior, and the influence of imperfections on the condition for localization of deformation. The knockdown factor of the elastic bifurcation stress due to matrix and fiber non-linearities is studied first. Finally, the sensitivity of the kink stress to fiber misalignments and the most critical kink band inclination is studied.