The Dynamic Mechanical Behavior And Failure Mechanism Of Sandwich Shells With Metallic Foam Cores Under Intensive Loading

Ultra-light high porosity cellular metal, including the ordered lattice material and the disordered open-cell and closed-cell foam, is a new type of structural and functional engineering material. Due to the specific micro-structure topology of multi-scale cell size and rich cell configurations, excellent mechanical properties of high specific stiffness and energy absorption, and the other good physical performances in the damping, thermal, acoustics, electromagnetism, filtration and separation fields, cellular metal has more and more important application prospects in noise elimination, vibration insulation, separation engineering, electromagnetic screening, cushioning device and so forth. A typical sandwich structure consists of two thin face sheets adhered to a thick cellular metal core, so as to utilize the properties of each component for the structural advantage of the whole assembly. The mechanical behavior of sandwich structures subjected to quasi-static and impact/blast loading is of current academic and industrial interest. Sandwich shell, a better combination of the advantages of the shell and sandwich structures, is expected and would thereby be of great importance for its applications. However, few systematic studies have been reported on metallic sandwich shells under blast/impact loading, and no analytical models have been developed to date.In this research, experimental, computational and analytical investigations were conducted on a number of peripherally clamped sandwich shells with aluminum foam cores subjected to either blast or impact loading. Three different case studies to determine the blast and impact resistance performance of sandwich shells were conducted:(1) Deformation/failure modes and plastic dynamic response of metallic sandwich shells under blast loading;(2) Dynamic behavior of sandwich shells subjected to metal foam projectile impact; and (3) Preliminary optimal design of sandwich shells. The current work focuses on the deformation/failure patterns, energy absorption, deformation mechanism and shock-resistance performance of sandwich shells under various loading conditions. The main achievements are as follows:A self-developed ballistic impact pendulum system was employed to investigate the deformation and failure of sandwich shells subjected to different loading impulse levels in the blast test, as well as a new impact loading method was developed in the projectile impact experiment. Several typical dynamic failure modes of specimens can be observed, i.e. indentation and tearing failure of front face sheet, collapse failure of core, large inelastic deformation and shear tearing failure of back face sheet, and the interfacial delamination between face sheet and core. A parametric study was conducted and the results show that the back-face deflection of sandwich shells is sensitive to structural configuration and applied impulse. According to dynamic strain gauge test results, the deformation of sandwich shells may be divided as three zones, that is, pure bending region, bending and stretching region, and pure stretching region. The deformation governed by bending moment and membrane force is dominant in the pure bending and stretching regions, respectively. And the specimens were simultaneously subjected to bending moment and membrane force in the transition region.Based on the experiments, corresponding finite element simulations have been undertaken using commercial LS-DYNA software. In the simulation work, the explosive loading process and response of the sandwich shells were investigated. Energy absorption and the effect of plastic stretching and bending were also discussed. Results show that energy absorption capability of sandwich shells enhance with the increase of impact velocity, and decrease of face-thickness, curvature radius and core relative density. The coupling between core compression and combined bending and stretching stage is related to loading intensity, core strength and core thickness. It is clear from the near-optimal design of sandwich shells that the optimal structural configuration of sandwich shells with R=250mm and M/pfL=0.025subjected to/(Mσfy/pf)≤0.07is as follows:p=0.06, hc/L=0.06. In view of the human body damage mechanism, a reasonable try, taking peak value of impact acceleration of mid-span of sandwich shell as evaluation index of its shock resistance performance, was made in the paper.On the base of the analytical models of sandwich beam and panels under blast loading, due to the duration of blast loading is shorter comparison with the total response time, the dynamic response of sandwich shells can be divided into three sequential stages. A rigid plastic analytical model has been developed in this study. The research results are of worth to the theoretical prediction and engineering application of metallic sandwich shell.