Composite structures design and analysis

Abstract

Recent improvements in manufacturing processes and materials properties associated with excellent mechanical characteristics and low weight have become composite materials very attractive for application on different types of structures. However, even new designs are still very conservative, because the composite structure failure phenomena are very complex. This chapter shows the principal fundamentals to design and analyze composite structures. In the introduction, there is a definition and a classification of composite materials, as well as motivation, considering advantages and challenges to design by using this type of material. Thus, it is presented a methodology to design composite structures in order to overcome the main challenges related to this task. In this methodology, it is found three important analyses: Micromechanical, macromechanical, and failure analyses. In order to perform micromechanical analysis, it is necessary to know more about matrix, reinforcements, and interfaces. For example, in this chapter, it is addressed only polymeric matrix and long fibers as reinforcements, which are combined to create an orthotropic ply. Then, different plies can stack with fibers oriented in different directions, creating an anisotropic or orthotropic laminate. The material properties of the ply can be obtained by Rule of Mixture or via mechanical testing. Hence, it is commented some difficulties to carry out experiments on composite materials and how is complicated to obtain allowable values for laminates. Based on the material properties, it is possible to calculate strain in the laminate, as well as strain and stress distribution in each ply. To perform the macromechanical analysis, it is possible to use Classical Laminate Theory (CLT). Thus, it is shown all hypothesis adopted for that theory and the implications generated by these ones. Finally, based on the actuating stress or strain values in each ply and allowable values of the used composite material, it is calculated the margin of safety for the plies by applying a failure criterion. In fact, for laminate structures, failure phenomena include intralaminar damages and interlaminar failures (delaminations), which are very complicated to be predicted via any failure theory. Therefore, even nowadays, many researchers have developed different failure theories to improve the design and analysis of composite structures.