CHARACTERISATION AND MODELLING OF THE FATIGUE DAMAGE AND FAILURE IN WOVEN COMPOSITES

The PhD thesis aims to deepen the fatigue behaviour of textile composites, with particular focus on woven fabrics. The high specific stiffness and strength, together with a great formability, make them key materials for lightweight structural applications. Relevant examples are the emerging fields of sustainable mobility and wind energy. The efforts were therefore aimed at understanding and modelling the damage mechanisms induced by fatigue, considering the effect of peculiar aspects of fabrics, from the reinforcement architecture and the number of layers to shifting and nesting phenomena. The experimental activities started from the manufacturing and testing of single woven layer specimens with different architectures. The layup allowed the in-situ quantitative monitoring of the crack evolution, focusing on the effect of the weaving pattern. The experimental campaign continued testing multilayer woven composites, analysing the interaction between overlapped layers in a nested configuration. Regarding the modelling activities, a multiscale strategy is developed, with the aim of estimating the elastic properties and the local stresses in the bundles, predicting the first crack initiation in woven composites. An analytical model, based on a shear-lag analysis, is proposed, allowing to relate the damage in terms of cracks to the stiffness degradation. Eventually, an analytical damage-based model for the prediction of crack density evolution is developed.