Most of the existing materials around us can be considered composite materials, since they are composed by several phases or components at certain spatial scale. The physical and chemical properties of composites, as occurs with structures composed by two or more materials, is defined by the response provided by their constituents. Therefore, a good characterization of the composite requires considering the performance of its components. In the last decades, several methods have been proposed with this approach to characterize composite materials, most of them based on multiscale techniques. Nowadays, multiscale homogenization analysis is a popular topic in the simulation of composite materials. This is because the complexity of new composites demands of advanced analysis techniques for their correct characterization, and thanks to the continuous increase of computational capacity. However, the computational cost when multiscale procedures are taken to the non-linear range and are applied to real-size structures is still excessively high. In this context, this work presents a comprehensive homogenization formulation for an efficient non-linear multiscale modeling of composite structures. The development of a composite multiscale constitutive model is addressed from two different homogenization approaches. The first one corresponds to a phenomenological homogenization procedure for the non-linear analysis of carbon nanotubes reinforced composites. The second one is a general two-scale homogenization procedure to analyze three-dimensional composite structures. Carbon nanotubes (CNTs) have been regarded as ideal reinforcements for high-performance composites. The formulation developed takes into account explicitly the performance of the interface between the matrix and the CNTs. The load is transferred to the nanotubes through the considered interface. The composite non-linear behavior results from the non-linearities of its constituents, and in case of interface damage, it also becomes non-linear the law defined to couple the interface with the CNTs. The formulation is validated studying the elastic response and non-linear behavior of several composites. In the context of multiscale homogenization, a first-order and an enhanced- first-order formulation is developed. The results obtained for laminate composites using the first-order formulation are compared with other microscopic formulations, showing that the homogenization method is an excellent alternative when microstructural effects must be taken into account. Then, a strategy to conduct non-linear multiscale analysis in an efficient way is proposed. The procedure conserves the dissipated energy through the scales and is mesh independence. The analysis of academic examples is used to show the capacity of the non-linear strategy. Finally, the simulation of an industrial composite component proves the performance and benefits of the non-linear homogenization procedure developed.

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