Estimation of lamina stiffness and strength of quadriaxial non-crimp fabric composites based on semi-laminar considerations

Quadriaxial non-crimp fabric (QNCF) composites are increasingly being used as primary structural materials in aircraft and automotive applications. Predicting the mechanical properties of QNCF lamina is more complicated compared with that of unidirectional (UD) composites, because of the knitting connection of different plies. In this study, to analyze the stiffness and strength of the QNCF composites, a novel modeling strategy for the meso-scale features is presented based on the semi-laminar assumption. Following the view of the mechanical properties of single composite lamina, the complex QNCF layer is decomposed into individual plies. Three different representative unit cells along fiber direction are selected to predict the mechanical performance of QNCF, including in-plane stiffness, damage initiation, and stiffness degradation. To validate the developed modeling strategy, the predictions are compared with existing experimental results, where a good agreement is presented on the prediction of in-plane stiffness and strength. Furthermore, the effect of in-plane fiber distortion, induced by the stitching yarn on the mechanical properties, is studied.