臺灣博碩士論文加值系統

　　由於泡沫材料已漸廣泛應用於輕質三明治板之心材，而且此類輕質結構所處環境多屬一多軸載重的狀態，因此，對於輕質三明治板而言，泡沫心材於多軸載重作用下之力學性質與可能破壞機制所對應的破壞準則，成為分析與設計輕質三明治板之重要依據。但由於泡沫材料的製造過程容易導致其微觀結構呈現非均向性，因此，泡沫材料的力學性質與可能破壞機制，將受到其內部幾何結構亦即非均向比之影響。本研究將推導非均向性開放型泡沫材料之多軸破壞包絡面，藉由探討不同可能破壞機制之破壞準則，進而組構此泡沫材料之多軸破壞包絡面，所分析之破壞機制包括塑性降伏、脆性破壞、彈性挫屈及拉裂破壞等。最後，針對開放型泡沫材料於軸對稱載重條件下，將前述各可能破壞機制之破壞準則相互比較，以獲得所對應之多軸破壞包絡面，然後，分析並探討非均向比將如何影響開放型泡沫材料之力學行為與其多軸破壞包絡面。

　　Open-cell foams are typically used as core materials in lightweight sandwich panels which are always subjected to a general state of multiaxial stresses. Thus, the mechanical properties and the failure criteria corresponding to different failure mechanisms for open-cell foams under multiaxial stresses are essential and important to the structural integrity of lightweight sandwich panels. Since open-cell foams are normally anisotropic due to processing, their mechanical properties will be affected by their cell geometry, namely the anisotropy ratio. In this paper, the failure envelopes of anisotropic open-cell foams are generated and presented. Different failure mechanisms including plastic yielding, brittle crushing, elastic buckling and fracturing are taken into account to construct the failure envelopes of anisotropic open-cell foams. For the case of axisymmetric stress state, the effects of the anisotropy ratio on the mechanical behavior and the failure envelopes of open-cell foams are evaluated.

Chapter 1 Introduction----------------------------1

Chapter 2 Literature Review-----------------------4
2.1 Plastic yielding----------------------4
2.2 Brittle crushing----------------------6
2.3 Elastic buckling----------------------8
2.4 Brittle fracturing--------------------8

Chapter 3 Plastic yielding-----------------------13
3.1 Uniaxial plastic yielding strength---13
3-1-1 Along the X3 direction---------14
3-1-2 Along the X1 or X2 direction---14
3.2 Pseudo-isotropy for anisotropic
open-cell foams----------------------15
3.3 Fully plastic moment for multiaxial
stresses-----------------------------16
3.4 Plastic yielding of anisotropic
open-cell foams----------------------17
3-4-1 Along the direction----------17
3-4-2 Along the X1 or X2 direction---19
3-4-3 Results and discussio----------20

Chapter 4 Brittle Crushing-----------------------31
4.1 Uniaxial brittle crushing strength---31
4-1-1 Along the X3 direction---------31
4-1-2 Along the X1 or X2 direction---32
4.2 Pseudo-isotropy for anisotropic
open-cell foams----------------------32
4.3 Rupture moment for multiaxial
stresses-----------------------------33
4.4 Brittle crushing of anisotropic
open-cell foam-----------------------33
4-4-1 Along the X3 direction---------33
4-4-2 Along the X1 or X2 direction---35
4-4-3 Results and discussion---------36

Chapter 5 Elastic Buckling-----------------------45
5.1 Rectangular hexagonal prism model----47
5.2 Analysis for the elastic buckling of
anisotropic foams--------------------47
5-2-1 Mode I-------------------------49
5-2-2 Mode II------------------------51
5-2-2-1 Mode II-1--------------52
5-2-2-2 Mode II-2--------------54
5-2-3 Mode III-----------------------55
5-2-3-1 Mode III-1-------------56
5-2-3-2 Mode III-2-------------58
5.3 Results and discussion---------------59

Chapter 6 Brittle Fracture-----------------------84
6.1 Analysis for brittle fracture--------84
6-1-1 Along the X3 direction---------85
6-1-2 Along the X1 or X2 direction---87
6-1-2-1 Type I-----------------87
6-1-2-2 Type II----------------89
6.2 Results and discussion---------------90

Chapter 7 Failure Envelopes---------------------108

Chapter 8 Conclusions---------------------------122

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