Static and Dynamic Behavior of Functionally Graded Carbon Nanotube-Reinforced Laminated Composite Doubly-Curved Shells: Higher-Order Structural Approaches

Shell structures are broadly employed in many engineering applications due to their efficiency in bearing with external loads, a high degree of resistance, remarkable stiffness and a high strength-to-weight ratio. These peculiar features are given by the doubly-curvature that defines their reference surface. Recently, the need of higher level performances has led to a greater use of innovative materials in shell design, such as fiber-reinforced composites, sandwiches and nanostructures. As a consequence, new materials have been introduced to design stiffer structural elements, without increasing their weight. Analogously, these advanced materials have allowed to improve their mechanical behavior, increasing for instance the safety requirements and the opposition to delamination phenomena. Advancements in manufacturing process have led to the consequent development of the so-called smart structures, which are currently the main topics of many researches and applications. A clear example of this aspect is given by the increasing use of Carbon Nanotubes (CNTs) as reinforcing phase of many composite materials. Nevertheless, since their first applications several mechanical models have been proposed to characterize these nanoparticles. A new micromechanical approach which deals with the agglomeration effect of CNTs is followed by the authors. The key point of this model consists in assuming that the distribution of CNTs in a polymer matrix is irregular. Consequently, their concentration is not uniform since they tend to concentrate in spherical shaped inclusions. The homogenization process based on the Mori-Tanaka scheme is used to compute the effective mechanical properties of such composites.