MULTISCALE AND MULTIPHUSIC FEM BASED NUMERICAL APPROACHES IN MECHANICS OF COMPOSITE MATERIALS

Composite materials are ideal for structural application where high strength-to-weight and stiffness-to-weight ratio are needed. Most of modern technologies require material offering peculiar combinations of several properties that cannot be found in traditional materials as metals, ceramics and polymers. The study of composite material actually involves many topics, such as manufacturing processes, non linearity constitutive behavior, strength of materials and micromechanics. The progress in technologies has allowed the development of analytical and numerical procedures that are nowadays essential to characterize the behavior of materials. This work addresses several finite element approaches that have been adopted to simulate the behavior of several composite structures. In particular, in the first chapter, the anisotropic constitutive behavior of ALCANTARA® tissue is modeled introducing both linear anisotropic laws and non-linear hyperelastic model, the latter by the definition of Helmholtz free energy and set up specific microstructure tensor. The modeling of non-linear constitutive behavior permits to simulate the characteristics of both manmade composite material, where the optimum mechanical performance are searched, and organized biological composite structures, where the optimization structural process is adopted. It is well now that, on account of the presence of solid and fluid constituents at micro-scale level, many biological soft tissues exhibit an overall macroscopic non linear elastic or poro-elastic mechanical behavior too. In this respect, in the second chapter, the biomechanics of corneal structure is modeled through a FE multiphysic approach (thermo-mechanical) in orde to simulate its viscoelastic behavior in the outcome of Conducted Keratoplastic surgery (Fraldi et al. 2010). A new multi-scale, three-dimensional finite element model of the cord rubber lamina, based on a hybrid analytical/numerical approach, has been developed in the third chapter. Unlike the aforementioned orthotropic approach that are commonly adopted in modeling unidirectional laminae, the capability of this model relies on the possibility of simulating the tension-twisting coupling of the cord and, in turn, of the overall composite, which determines a peculiar stress state in the interfacial zone and matrix. Cord behavior has been first modeled by using Costello's analytical model, which accounts for tension-twisting coupling and relates the cord constitutive behavior to the hierarchical structure of the cord itself. Finally, on the basis of this analytical model, a homogenized cylindrical cords model, embedded in a rubber matrix, have been implemented in the FEM code. In conclusion, in the light of the scientific and practical interest in the mechanical response of polymeric thin films utilized for food packaging, the mechanisms governing the delamination phenomena observed experimentally in multilayer films during HPP have been investigated in order to pave the way for optimal design of packaging structures. To make this, both analytical and Finite Element (FE) analyses of the process of HP treatment of pouches made of multilayer films and containing tap water have been performed