Optimum Design Of Multi-functional Honeycomb Structures

Honeycomb structures are important attractive material systems for their lightweight and potential multi-functionality. Recently, many researchers in the academic and engineering community are devoted to this promising research area. The present dissertation studies the honeycomb structures through theoretical analysis, numerical simulations and optimizations, and experimentations. Since thermal and mechanical loading is critically important for many applications, the structural performances investigated herein are heat dissipation property, mechanical load capability and energy absorption performance. In the last part of this dissertation, we give a brief study on the manufacture method for the honeycomb structures.The main works of the dissertation are as follows:1. Heat dissipation property of sandwich structures filled with super-cell honeycomb core, which is core consisting of many different shaped cells, has not been seen in literatures. The present work applies an approximate procedure to estimate the effective Nu coefficient and iRe factor (f and Re are Fanning coefficient and Reynolds number respectively). Based on the effective medium model, an analytical study is carried out for sandwich panels and cylindrical structures with honeycomb cores aiming at maximization of heat dissipation efficiency while maximizing mechanical stiffness. Two non-dimensional indexes which are accepted in the engineering field are used to measure structural heat dissipation performance and heat dissipation-mechanical load capability respectively. Our results show that Kagome cells are superior to other traditional single shaped cells from the viewpoint of multifunctionality. The relationship between the optimization of engineering multifunctional indexes and the multi-objective optimization formulation is discussed and the shortage of multifunctional index is discussed. ( In Chapter 2)2. The multifunctional optimization of sandwich panels and square section prism structures filled with orthotropic honeycomb cores is investigated. Rectangular and isosceles triangle cells are taken as examples. Based on the engineering optimization index on heat dissipation-mechanical load performance, two level programming models are constructed in order to obtain Pareto set of multi-object optimization design. Compared with optimization of the single specific index, the presented method offers a wide design choice for the engineers. ( In Chapter 3) 3. We further study an optimization of non-uniform distribution of honeycomb materials. In order to obtain the concurrent optimum design of material and structures, two classes of design variables, local relative density and cell size are chosen. Structural topology optimization approach is applied to develop an mathematical formulation of heat dissipation optimization. Based on the insights from numerical results, a general rule for optimum cell distribution is observed. Cells of high density and small aperture are arranged in the domain of high temperature gradients, while cells of low density and big aperture are arranged in the domain of low temperature gradients. Nearly uniform temperature gradients are usually associated with the optimum material distribution. The heat dissipation index of optimum non-uniform design is increased remarkably in comparison with the optimum uniform design. For all density cells structures, a bi-objective optimization problem is studied, i.e. structural compliance minimization in-plane together with efficiency of heat dissipation. Based on the multifunctional optimization index, sub-Pareto-sets are obtained for different design intentions. ( In Chapter 4)4. For different cell morphologies, the multifunctional design of honeycomb structures based on the topology optimization technique. Three-dimensional variation of temperature is considered. Since the pressure drop is concerned differently in different applications, two optimization models, i.e. optimum heat dissipation performance model and maximum heat transfer model are constructed. A real size CPU cooler and a monolithic catalyst supports of chemical reactor are optimized numerically. The numerical results suggest that the Optimum Topology Design (OTD) would become more and more valuable as the fluid velocity increases. It also shows that OTD can increase the Heat Dissipated Rate and the diameter of catalyst supports which lead to improve operation and economics of gas-solid exothermic reaction. ( In Chapter 5)5. A "Strip slotting-Assembling-Welding" manufacture method is applied for making the PVC and PP based honeycomb structures of different inner cell topology. The in-plane compression and impact behavior are investigated by the experiment and numerical simulation for Kagome and other cell structures. The digital image correlation (DIC) method is applied to obtain the all field strain of structures in the experiments. Experiments and simulations suggest that the energy absorption performance of Kagome is superior to other structures with the same materials volume and structural sizes. Finally, the deformation mechanism of Kagome honeycomb structures is addressed. ( In Chapter 6) The research of this dissertation is supported by the Excellent Doctoral Dissertation Sustentation Fund of Dalian University of Technology (2005.4～2007.4) ,Major Program (No. 10332010), Major Research Plan (No.90205029) and Program for Innovative Research Team (No.10421202) of the Natural Science Foundation of China. The financial contributions are gratefully acknowledged.