Nonlinearities in mechanical behavior of textile composites

In several configurations of fabrics, the fiber waviness can be significantly reduced under loading, introducing important modifications of mechanical behavior, mainly concerning the in plane textile stiffness; the phenomenon is of capital importance if the material has to be applied in single ply configuration. In the present paper a numerical approach is proposed for simulation of nonlinear behavior of some textile composite layouts. The attention has been focused on plane weave textiles for aerospace and general applications: a triaxial carbon fiber/ester-cyanate resin and a biaxial glass fiber/PP textiles, which have been characterized on the basis of experimental or bibliography data, focusing the attention on main mechanical properties and their variation with the strain level in the material. Experimental data show the importance of nonlinear effects mainly caused by the variation of the waving of fibers under loading. A numerical analysis based on the use of standard finite element method has been developed, modeling the textile structure at a semi-microscopic level. Basic laminar theory has been used to calculate the elastic properties of a single yarn, whose geometry has been identified. Numerical results demonstrated the ability of the model to describe the textile behavior and appears a powerful tool for development of new layouts to define the best textile configuration for the specific application.