仿生梯度材料之機械性質模擬與分析

Abstract

近年來對於材料的開發有了不同於以往的方向，眾多生物的結構成為新穎高性能材料之設計靈感。具特殊結構元素的自然材料使得生物具備了適應大自然複雜力學環境的能力，這些天然材料大多數是由簡單的原材料例如礦物質、蛋白質複合而成。其中，梯度結構是自然界中常見的性能優化策略之一，基本的軟硬材透過梯度分布方式能夠使其性能超越人造材料，因此本研究將探討具梯度結構的複合材料對機械性能之影響。 本研究致力於使材料能夠具備高韌性卻不失強度，為了模擬不同梯度模型的力學性質，使用二維三角晶格彈簧的模型及電腦計算方法，預測仿生材料的裂縫發展以及機械性質。本論文梯度的設計可以分為結構梯度以及材料梯度。結構梯度為模仿竹子維管束由中心至表面分布不均勻的形貌，進而提出了包含仿維管束形狀的拓樸軸長比、拓樸數量、梯度層數、拓樸水平與垂直距離以及梯度方向等六種獨立的設計參數以及不同參數對力學性能的影響，找到最佳參數組合並歸納出以結構變化為梯度的設計方向。 除了結構梯度，本論文也固定拓樸為無梯度的均勻結構，加入了第三種材料:介質材料(Medium)。而這種由三種材料複合而成的新的梯度設計策略為材料梯度。在本研究中將材料梯度分為層狀(Layer)以及階層式(Hierarchical)的材料梯度，其中層狀梯度包含了正向及反向。本論文除了提出階層式梯度的四種梯度模式，也結合了三種不同階層結構的設計。透過這些變化，結合階層化設計與仿竹子的結構梯度，最終設計出同時具備高強度以及高韌性的階層化仿竹子梯度結構，在維持強度的情況下，韌性可大幅提升。

In recent years, the development of materials has been different from the past, and the structure of many organisms has become the inspiration for the design of new and high-performance materials. Natural materials with special structural elements enable creatures to adapt to the complex mechanical environment of nature. Most of these natural materials are composite from simple raw materials such as minerals and proteins. Among them, the gradient structure is one of the common performance optimization strategies in nature. The basic soft and hard materials can make their performance surpass man-made materials through the gradient distribution method. Therefore, this study will explore the effect of composite materials with gradient structure on mechanical properties. This research aims to make materials with high toughness without losing strength. In order to simulate the mechanical properties of different gradient models, a two-dimensional Lattice Spring Model (LSM) and computer calculation methods are used to predict the crack development and mechanical properties of bio-inspired materials. The design of gradients in this thesis can be divided into structural gradients and material gradients. The structural gradient is to imitate the maldistribution of bamboo vascular bundles from the center to the surface. Then, the topology axis length ratio, the number of topology, the number of gradient layers, the horizontal and vertical distances of the topology, and the direction of the gradient are proposed. Theses six independent design parameters and the influence of different parameters on the mechanical properties were found, and the optimal parameter combination was proposed, also the development of the future gradient design direction with the structural change was summarized. In addition to the structural gradient, this thesis also fixed the topology to a uniform structure without gradient, and added the third kind of materials: Medium. With Medium material, the new strategy of gradient design is material gradient, which is compounded of three materials. In this study, material gradients are divided into Layer and Hierarchical material gradients. The Layer gradients include normal and transverse direction. In addition to propose the four Hierarchical gradient modes, this paper also combines three different hierarchical structures with gradient modes. Through these design changes, a material gradient structure with both high strength and high toughness is finally achieved, and the toughness can be greatly improved while maintaining the strength.