臺灣博碩士論文加值系統

本研究針對具曲度及變剖面微觀構件之雙缺陷蜂巢材料進行廣泛性之研究並探討此二類微構件缺陷單一存在或同時存在時對蜂巢材料機械性質之影響。首先利用巨觀參數相對密度及微觀參數 及 定義最小重複單元體之理論模型，並以樑之變形理論分析蜂巢材料於平面上之機械性質，包括楊氏模數、柏松比、彈性挫曲強度、塑性降伏強度、脆性破裂強度及雙軸應力作用下之破壞包絡面。並利用有限元素套裝軟體ABAQUS建立具曲度及變剖面微觀構件蜂巢材料之數值分析模型，理論與數值結果皆顯示其力學性質受其幾何形狀參數所影響，並發現當蜂巢材料具曲度及變剖面微構件雙缺陷時，其正規化強度為蜂巢材料具其中一種單一缺陷所求得正規化強度之相乘值。當蜂巢材料承受平面上雙軸應力作用時，其可能破壞機制包括：彈性挫曲、塑性降伏及脆性破裂等，同時考慮上述破壞機制並利用本文所獲得之結果，可進一步求得具曲度及變剖面微觀構件蜂巢材料承受雙軸應力作用時之破壞包絡面，以利工程實際運用所需。

Aim of this study is to investigate the effects of the microstructural imperfections of solid distribution in cell edges and curved cell edges within honeycombs on their mechanical behavior when each single imperfection or dual imperfections are taken into account. The analytical expressions for describing the elastic moduli, plastic collapse strength, brittle crushing strength, elastic buckling strength, yield surfaces and brittle-fracture surfaces of regular hexagonal honeycombs with imperfections were derived from a model of curved cell edges with Plateau borders. Finite element numerical analyses on the mechanical properties of hexagonal honeycombs with dual imperfections were also performed and then compared to the proposed theoretical modeling. Both analytical and numerical results indicate that the effects of dual imperfections are more significant as compared to those of each single imperfection. Moreover, the normalized stiffness and strengths of a hexagonal honeycomb with dual imperfections are found to be approximately equal to the products of those with each single imperfection. In other words, the stiffness and strengths of a hexagonal honeycomb with dual imperfections can be directly estimated from those with each single imperfection. Furthermore, the failure surfaces of honeycombs with dual imperfections are developed; the effects of solid distribution in cell edges and curvature of cell edges on the mechanical properties of honeycombs are also evaluated.

Abstract…………………………………………………………………………………………I
Acknowledgements……………………………………………………………………………III
Table of Contents……………………………………………………………………………IV
List of Tables…………………………………………………………………………………VI
List of Figures………………………………………………………………………………VII
Chapter 1 Introduction………………………………………………………………………1
1.1 Literature Review…………………………………………………………………2
1.2 Scope of Thesis………………………………………………………………………………6
Chapter 2 Cell Geometry……………………………………………………………………………8
2.1 Honeycombs with Single Imperfection…………………………………………8
2.1.1 Honeycombs with Plateau Borders………………………………………………8
2.1.2 Honeycombs with Circular Cell Edges…………………………………………10
2.2 Honeycombs with Dual Imperfections……………………………………………11
Chapter 3 Analysis for Honeycombs with Single Imperfection………………………23
3.1 The In-plane Properties of Honeycombs with Single Imperfection:
Uniaxial Loading…………………………………………………………………24
3.1.1 Honeycombs with Plateau Borders ……………………………………………24
3.1.2 Honeycombs with Circular Cell edges…………………………………………26
3.2 The In-plane Properties of Honeycombs with Single Imperfection:
Biaxial Loading……………………………………………………………………27
3.2.1 Honeycombs with Plateau Borders ……………………………………………27
(a) Yield Surface………………………………………………………………27
(b) Brittle-Fracture Surface…………………………………………………28
3.2.2 Honeycombs with Circular Cell edges………………………………………34
(a) Yield Surface………………………………………………………………34
(b) Brittle-Fracture Surface…………………………………………………37
Chapter 4 Analysis for Honeycombs with Dual Imperfections………………………44
4.1 The In-plane Properties of Honeycombs with Dual Imperfections:
Uniaxial Loading……………………………………………………………………45
4.1.1 Elastic Moduli……………………………………………………………………45
4.1.2 Plastic Collapse Strength………………………………………………………48
4.1.3 Brittle Crushing Strength………………………………………………………50
4.1.4 Elastic Buckling Strength………………………………………………………52
4.2 The In-plane Properties of Honeycombs with Dual Imperfections:
Biaxial Loading……………………………………………………………………56
4.2.1 Yield Surface………………………………………………………………………58
4.2.2 Brittle-Fracture Surface………………………………………………………60
Chapter 5 Effects of Imperfections on Stiffness and Strength……………………69
5.1 Numerical Analysis………………………………………………………………69
5.2 Effect of ………………………………………………………………………71
5.3 Effect of …………………………………………………………………………75
5.4 Effect of both and ……………………………………………………………77
5.5 Correlation between dual imperfections and single imperfection………80
Chapter 6 Effects of Imperfections on Failure Surfaces……………………………113
6.1 Numerical Analysis for Biaxial Compressions………………………………113
6.2 Failure Surfaces for Ductile Honeycombs……………………………………116
6.3 Failure Surfaces for Brittle Honeycombs……………………………………118
Chapter 7 Conclusions and Suggestions…………………………………………………140
7.1 Conclusions…………………………………………………………………………140
7.2 Suggestions…………………………………………………………………………143
Reference………………………………………………………………………………………145

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