生物經過物競天擇演化出複雜之多階層結構，提供多功能性與出色的機械性能以應對環境的挑戰。因此，材料科學家持續研究生物材料，找尋更有效率的解決方案以解決各個工程領域的問題。在能量吸收方面，柑橘類果皮具有多孔結構，使其擁有衝擊保護與顯著的能量耗散特性，以避免果實成熟落下後撞擊地面所造成之損害。觀察果皮之組成，可發現海綿狀之中果皮佔據大部分體積，並由鬆散的生物細胞包圍緻密的維管束組成。
由柑橘皮組織的細胞排列啟發，本研究設計了一種新穎的能量吸收器，選用六角形蜂窩對多孔細胞進行建模，並於傳統蜂窩結構中規則填入自相似之第二階層結構，形成具有疏密相間結構層次之新型仿生設計。本研究中利用熔融沈積建模 (FDM) 製造三維實體，並施以單軸向準靜態壓縮測試，探討這種結構的能量吸收能力和面內變形行為，並通過改變各種幾何設計參數，建立結構-性質-功能之關係。而在理論與數值研究上，我們通過有限元分析對仿生啟發之多階層蜂窩結構進行模擬，以闡明其於壓縮測試下之變形行為與應力分佈。此種具有輕量化與可回復特性的仿生結構不僅有特殊的兩段式緩衝機制，亦能透過設計產生可預測之變形行為，為工程領域之能量吸收與可預測行為等相關應用提供嶄新視角。

Through natural selection, many different organisms have evolved hierarchical structures at varying scales, providing multifunctionality and outstanding mechanical performance to deal with environmental challenges. Therefore, materials scientists have been studying and learning from biological materials to find out more efficient solutions to problems in various engineering fields. In terms of energy absorption, the citrus peels have porous structures, which provide impact protection and significant energy dissipation properties, to avoid damage caused by the fruits hitting the ground when they are ripe and fall. From the composition of the pericarp, it is discovered that the spongy mesocarp occupies most of the volume and consists of dense vascular bundles surrounded by loose biological cells.
Inspired by the cell arrangement of the citrus peel tissue, we have proposed a novel energy absorber. Regular hexagonal honeycombs have been selected to model the porous cells, and traditional honeycomb structures have been regularly incorporated with self-similar second-level units to form a novel bioinspired design with an alternative sparse and dense structural hierarchy. In this study, the three-dimensional entities are fabricated by fused deposition modeling (FDM) and subjected to uniaxial quasi-static compression tests to investigate the energy absorption abilities and in-plane deformation behavior. By tuning various geometric design parameters, the relationship between structures, properties, and functions has been established. In terms of theoretical and numerical research, the simulation has been performed by finite element analysis (FEA) to elucidate the deformation behavior and stress distribution of the two-order hierarchical honeycomb structures under compression tests. Such lightweight and recoverable bio-inspired structures have a special two-stage impact protection mechanism and predictable deformation behavior through proper design, providing a brand-new perspective for engineering fields in energy absorption, predictable mechanical responses, and so on.

摘要 i
Abstract ii
致謝 iv
Content vi
Figure Caption ix
Table Caption xxviii
Chapter 1. Introduction 2
Chapter 2. Literature Review 4
2.1 Inspirations from Plants 4
2.2 Energy Absorption of Cellular Solids 10
2.3 Additive Manufacturing of Bio-inspired Materials 15
2.4 Finite Element Analysis in Energy Absorbers 19
Chapter 3. Experimental Process 23
3.1 Observation of Citrus Peels 25
3.2 Model Designs of Honeycomb-based Bio-inspired Structures 28
3.3 Fabrication by Additive Manufacturing 37
3.4 Uniaxial Compression Test 40
3.5 Finite Element Analysis 42
Chapter 4. Results and Discussion 46
4.1 The Porosity of Citrus Peels 47
4.2 Mechanical Properties and Deformation Behaviors of Typical Citrus Peel-inspired Cellular Solids (I=7) 52
4.2.1 Determination of Four Compression Stages 52
4.2.2 Strain Rate Dependence 57
4.2.3 The Effect of Relative Densities 62
4.2.4 Finite Element Analysis 68
4.3 Models with Different Incorporation Amounts (I) of Hierarchical Units 78
4.3.1 In-Plane Compressive Properties 78
4.3.2 Energy Absorption Abilities 83
4.3.3 Finite Element Analysis 86
4.4 Models with the Same Densities (I=3) but Different Orientations 91
4.5 Models with Non-deflected Corner Elements and 60° Deflected Central Element (I=3) 95
4.5.1 Tailorable Two-Step Energy Absorption Profiles 95
4.5.2 The Predictable Deformation Behaviors with Different Locations of Missing Cell Wall 100
4.5.3 Finite Element Analysis 104
4.5.4 The Effect of Amounts of Missing Cell Walls on Performance 107
4.6 Summary: Design Strategies for Energy Absorbers 112
Chapter 5. Conclusions 115
Chapter 6. Future Works 119
References 123

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