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標題: | 脆性生物材料之破裂機制模擬─以鳥類蛋殼及空心樹幹為例 Simulation of Failure Mechanisms of Brittle Biological Materials: A Case Study of Avian Eggshells and Hollow Tree Trunks |
作者: | Ying-Chuan Kao 高穎全 |
指導教授: | 莊嘉揚(Jia-Yang Juang) |
關鍵字: | 擴展有限元素法,破壞,裂紋生長,截面扁平化,蛋殼,空心樹幹, XFEM,fracture mechanism,crack development,cross-section flattening,eggshell,hollow tree trunks, |
出版年 : | 2020 |
學位: | 碩士 |
摘要: | 材料的破壞是工程上一個不可或缺的領域,在自然界中也同樣非常關鍵,且生物材料通常具有更加複雜的結構和特殊的材料性質,故本研究旨在瞭解此種類型的材料破壞機制,以期提供與自然保育、生態演化與仿生設計等領域相關的深入解析。 本研究針對空心樹幹及鳥類蛋殼兩大主軸進行有限元素以及擴展有限元素模擬,對照各種幾何參數和材料參數的空心樹幹模型和解析解,定義出樹木的臨界彎矩比值來判斷其破壞機制屬於切向開裂破壞或典型彎曲破壞以及對應的破裂起始位置點,並藉由擴展有限元素模型驗證切向及縱向破裂面的生長方式,得到與解析解假設和實驗觀察一致的結果;而鳥類蛋殼的破壞機制探討則建立在前人的有限元素應力分析模型之上,針對眾多實驗結果當中最常見的兩種主要破壞方式,徑向破壞和環狀破壞,分別以雞蛋和鴕鳥蛋的壓縮試驗樣本建立對應的擴展有限元素模型,使用最大主應力準則及最大畸變能準則作為破壞起始條件,輔以內聚力模型方法模擬破裂面發展,重現了實驗所得的各式裂紋幾何和破壞所發生的臨界負載數值。 綜整理論、實驗以及模擬的結果,本研究提出了樹木留存強度監測的量化指標、探討了截面扁平化的影響和特定材料參數的重要性,且驗證了蛋殼的徑向破壞與環狀破壞之破裂起始位置分別位於蛋殼的內表面和外表面以及其中負載驟降幅度的差異等;在本研究的結果和建立好的擴展有限元素模型之上,未來能夠再深入探討更多幾何性狀和物種的破壞,還有多種破壞機制之間的拮抗關係。 As an important field in engineering, fracture mechanics of materials also plays a key role in the nature. Also, biological materials often possess special structures and much more complicated material properties than artificial engineering materials. Thus, this study aims to investigate those kinds of biological materials and their corresponding mechanisms of failure in order to provide insights for conservation of natural resources, research in ecology and the field of bio-mimic engineering design. This study is composed of two main topics, simulations of hollow tree trunks and simulations of avian eggshells. First, stress analysis through finite element model of hollow tree trunks of various geometry and properties provides results of critical bending moments for conventional bending failure and tangential cracking failure to occur. Then, extended finite element model (XFEM) of hollow tree trunks proves the inference of the analytical assumptions of the crack initiation position and developing direction of both failure mechanisms. Consistent results can be found between XFEM simulation and experiments. On the other hand, XFEM model of eggshells are established to depict the two most common fracture mechanisms in compression test experiments of avian eggs, the radial crack fracture and the ring crack fracture. The radial crack model is a model of hen eggshell and the ring crack model is a model of ostrich eggshell adopting the maximum principal stress criterion and the maximum distortion energy criterion, respectively. By including the cohesive zone material property method, crack surface development and corresponding fracture load of each egg samples are also reproduced. Through all the results of analytical analysis, simulations and experiment, this study provides quantification guides for strength loss of hollow tree trunks, the critical impact of cross-section flattening and specific material property settings. Also, the difference in crack initiation position and form of well-developed cracks and simultaneous force drop with eggshell failure are verified. Among the foundations and models provided through this study, further research about various geometries and species of trees and avian eggs or even other biomaterials can be discussed in the future. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/15415 |
DOI: | 10.6342/NTU202001870 |
全文授權: | 未授權 |
顯示於系所單位: | 機械工程學系 |
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