Mechanical Properties And Breakage Mechanism Of Cellular Materials

This dissertation consists of six chapters. The first chapter presents a comprehensive study of the historical and current studies in cellular materials. In chapter 2 and chapter 3 the microstructures and mechanical properties of cellular materials are theoretical analysed and experimental studies respectively. The destruct process of materials are discussed in chapter 4. In chapter 5 effects of defects on mechanical properties of materials are argument by theoretical analyzing and computer simulating. Lastly, this dissertation presents the conclusion and prospects of studies in cellular materials.By combining experimental study, theoretical analysis and numerical simulation, mechanical properties and fracture damage are analyzed thoroughly. Major contents and results are followed by these:1. The microstructures and deformation mechanism of foams are studied, it is pointed out that the principal factors which affect the mechanical properties of cellular material include eigen nature of cell wall material, size and morphology of cell and relative density. For the first time, a uniform formula of the relative density of honeycomb is established, which include the results by Gibson and Ashby.2. Parameters of symptom of anisotropy of unit cell shapes are put forward, and corresponding theoretical model is established. It is pointed out that most of the unit cells are commonly anisotropic, and cellular material which is constituted by periodically arranged unit cells shows anisotropy in macroscopic, only when representative units are arranged randomly out of order inside the solid, it shows statistical isotropy in macroscopic. Many unit cells with regular shapes only shows axial symmetry or multi- axial symmetry but not isotropy. There are some error in 《Cellular solids:structure and properties》 by Gibson and Ashby.3. Considering the cells in cellular material as a kind of inclusion, the equivalent elastic modulus of cellular material is educed using micromechanics method. Major results of the relative density-dependence of mechanical properties of cellular materials are summarized, and a cellular model of honeycomb is raised.