Research Of Dynamic Performance Of Cellular Materials And Their Unit Cells

As a kind of ideal energy absorption materials, cellular material has been widely used in different fields. How to realize the multi-objective optimal design of energy absorption material has become the frontier. So far, the basic mechanical properties of cellular materials have been obtained. However, due to the complexity of the material, and the limitation of the experiments, some basic problems about the material, even the unit cell, hard to be further clarified. Taking advantage of computational mechanics, based on the mechanical responses of unit cells, the numerical models of the unit cell and cellular materials are established in this dissertation. The dynamic properties of cellular materials are investigated. The main contents are as follows:(1) By comparing the numerical results with those from experiments, the deformation characteristics of a tube under lateral compression by two rigid plates are investigated. Considering ideal elastic-plastic and linear hardening elastic-plastic models, the formation and propagation of plastic hinge in the cross section of the tube are clarified. Based on these analyses, the explicit algebra equation describing the relationship between the load and the deflection of the tube is established. Comparison with experimental results indicates that this equation is efficient and accurate in predicting the mechanical properties of tube under lateral compression. Furthermore, it is easier for engineering application owing to its explicit algebraic form.(2) The large deformation behavior of a new type I-type II combined structure-ribbed tube laterally crushed by two rigid plates is investigated by explicit finite element method. An FE model of ribbed tube is established and mechanical responses and energy absorption characteristics of the combined structure are investigated. Critical angles are defined according to the deformation modes of ribbed tubes, and correspending algebraic formulas are proposed to predict the force-displacement relation of the ribbed tube in different cases. The results show that, the new proposed I-II combined ribbed tube takes the advantages of both type I and type II structures, and is better far the responses controlling.(3) Based on the concept of functional gradient, two-dimensional (2D) density graded circular honeycombs and three-dimensional (3D) density graded metal hollow sphere foams are established.The dynamic properties of the uniform cellular material and density graded cellular material with a constant relative density are analyzed. Base on the one-dimensional shock wave theory, a semi-empirical formula is obtained for predicting the dynamic plateau stress of cellular materials. The influence of lattice structures on the dynamic performance of metal hollow sphere foams is discussed.