A three-dimensional failure criterion for composites based on a new theoretical model of kink-band formation

A theoretical model for predicting kink-band formation in unidirectional composites is developed. In contrast to previous models, the proposed model takes into account the shear deformation in the non-misaligned regions when determining the fiber misalignment angle, and introduces an analytical approach for determining the orientation of the kink-band plane based on the applied stress state, instead of the conventional approach based on maximizing a failure index. Based on this model, a three-dimensional failure criterion for composites is further developed, which considers the effect of fiber misalignment under all stress states and therefore overcomes the discontinuity in the failure envelope produced by Pinho’s criterion. Using the proposed model and criterion, the failure behavior of unidirectional composites under various stress states is analyzed. A notable finding is that, under the σ 11 − τ 21 stress state, both longitudinal tensile stress and low longitudinal compressive stress can enhance the longitudinal shear stress at failure. The proposed criterion is validated against six sets of experimental data, with prediction errors of 1.77–11% and the lowest error in four of the six cases.