The Impact Characteristics And Multi-objective Optimization Of Metal Hollow Sphere Foam

With the quantity of domestic civil vehicle has been more than one hundred per one thousand people for the first time, the automobile industry has become a pillar industry of China. At the same time, people also pay more and more attention to the vehicle’s safety performance. Metal hollow sphere (MHS) foam as a new representative of the cellular materials has excellent impact energy absorption characteristic and tremendous potential for vehicle lightweight, which has wide engineering application in the field of automobile and rail transport. Impact Characteristics and multi-objective optimization of MHS foam were investigated using the finite element simulation method.Firstly, a three-dimensional compression experiment of Ping-Pong ball array had carried to discuss the basic impact characteristics of cellular materials, and the credibility of the finite element modeling method is validated using LS-DYNA simulation analysis. The effect of impacting velocity and densification point on MHS homogeneous foam was analyzed through the finite element simulation model. The results showed that the higher impacting velocity, the more obvious wave effect, and densification point would dramatically increase its distal end nominal stress. At the same time, specific energy absorption (SEA) and distal end stress (σd) were taken as shock performance indexes.Secondly, impact performance of MHS graded foam was studied based on finite element model, and deformation mode of MHS foam with gradient and anti-gradient was compared and analyzed under different impacting velocity, then it is concluded that the deformation mode of MHS foam is decided jointly by the weakest layer gradient and impacting velocity. Meanwhile, the effect of density gradient rank and number on the shock performance of the MHS foam were discussed, The results showed that the gradient rank and number have limited influence on the anti-shock performance of the MHS foam under a shock load with less obvious wave effect, i.e., the performance of the graded MHS foam is similar to that of the uniform density foam. However, when subjected to a shock with obvious wave effect, the MHS graded foam with more gradient number and anti-gradient rank shows the best performance.Furthermore, the cell lattice structure of the MHS foam was discussed in this paper. Six kinds of different space lattice structure of MHS foam had simulated by finite element model, and they are simple cubic, body-centered cubic, face-centered cubic, body-centered square, hexagonal close packing and triclinic arrangement respectively. The results showed that face-centered cubic MHS foam had optimal shock performance considering the energy absorption.Then, multi-objective design optimization (MDO) was performed for the face-centered cubic MHS anti-gradient foam. Based on impact energy absorption performance, the impact characteristic optimization model of MHS foam was built. The replaced model for shock performance prediction was established based on radial basis functions (RBF). The Pareto optimal solution set was obtained via the advanced genetic algorithm NSGA-Ⅱ. The results showed that the MHS foam had bigger energy absorption with large gradient and small gradient space near the proximal end simultaneously; and smaller distal end mean stress with small gradient and large gradient space near the distal end simultaneously.Finally, the MHS foam was applied in crashworthiness of vehicle as the filled material in energy absorption box and the front rail. The results showed that the MHS foam could partly improved the SEA of system through the simulation analysis, thus improved the passive safety performance.