臺灣博碩士論文加值系統

本研究的主要目的在於探討鋁合金7005擠製件的拉伸與疲勞性質。
在拉伸性質方面，討論高應變速率(1.85x10-2 s-1)及低應變速率(1.85x10-4 s-1)對拉伸強度、降伏強度及伸長率的影響，分析微結構變化對拉伸性質造成的差異。實驗結果顯示，高應變速率下應變硬化效果顯著，得到較高的拉伸強度及降伏強度；低應變速率下由於動態回復的多角化過程，得到次晶粒受應力作用拉長，因此有較高的伸長率。
疲勞性質方面，分析兩種高低反覆應力(240 MPa、180 MPa)的破壞模式與微結構改變之間的關係。實驗結果顯示，存在於試棒表面附近的介在物顆粒對疲勞壽命有很大的影響。在塑性變形過程中，若發生動態回復、多角化的現象，使晶粒軟化，疲勞裂縫呈現穿晶破壞模式，出現疲勞紋；若發生動態再結晶的現象，會出現細小的晶粒，疲勞裂縫呈現沿晶破壞，可以看到粗糙的破壞表面。最後利用可靠度統計分析中常用的韋伯分布函數來討論疲勞的破壞機率，並做疲勞壽命預測。

The aim of this study was to investigate the tensile and fatigue properties of as- extruded aluminum alloy, 7005.
Regrading to tensile properties, specimens were tested at higher strain rate (1.85x10-2 s-1) and lower strain rate (1.85x10-4 s-1) and showed the effects on the UTS, YS and elongation. As the experimental results indicated, the strain hardening effect under higher strain rate was more obvious and both the UTS and YS were higher. The polygonization of dynamic recovery under lower strain rate deformation resulted in subgrains stretched by tensile stress. So the elongation was higher, too.
In the part of fatigue property, the relationship between fractography and microstructure of specimens under two levels of repeated stress(240 MPa、180 MPa) was analyzed. As the experimental results indicated, the existent inclusion particles near specimen surface had a great influence on fatigue life. During the plastic deformation process, if dynamic recovery and polygonization occurred in the specimens, the grains were softened and the fatigue crack was transgranular fracture. Then the fatigue striations showed. If dynamic recrystallization occurred, the microstructure showed fine grains and the fatigue crack was intergranular fracture. The rough fracture surface was observed. Finally the statistical analysis of reliability, Weibull distribution function, was utilized to predict the fracture probability and fatigue life.

摘要…………………………………………………………………………………Ⅰ
Abstract……………………………………………………………………………Ⅱ
總目錄………………………………………………………………………………Ⅲ
表目錄………………………………………………………………………………Ⅴ
圖目錄………………………………………………………………………………Ⅳ
第一章 前言…………………………………………………………………….1
第二章 文獻介紹……………………………………………………………….2
2-1 鋁合金材料特性簡介……………………………………………………….2
2-2 鋁合金的分類……………………………………………………………….2
2-3 鍛造用鋁合金的特性……………………………………………………….3
2-4 鋁的FCC晶格結構………………………………………………………….6
2-5 拉伸試驗…………………………………………………………………….6
2-5-1 萬能試驗機…………………………………………………………….6
2-5-2 拉伸試驗應力分析…………………………………………………….6
2-5-3 真應力-真應變曲線……………………………………………………7
2-6 高週疲勞試驗……………………………………………………………….8
2-6-1 疲勞破壞……………………………………………………………….8
2-6-2 疲勞破壞之形貌特徵………………………………………………….8
2-6-3 旋轉樑疲勞試驗機之原理…………………………………………….9
2-6-4 疲勞應力分析………………………………………………………….9
2-7 韋伯分布在工程上的應用…………………………………………………12
第三章 理論探討………………………………………………………………13
3-1 疲勞裂縫起始與成長機構…………………………………………………13
3-1-1 疲勞裂縫起始機構……………………………………………………13
3-1-2 疲勞裂縫成長機構……………………………………………………13
3-1-3 疲勞試棒最後破斷處…………………………………………………14
3-2 可靠度和破壞機率分析：韋伯分布函數…………………………………14
3-3 動態回復(Dynamic Recovery ) …………………………………………16
3-4 動態再結晶(Dynamic Recrystallization) ……………………………17
第四章 實驗方法與步驟………………………………………………………19
4-1 實驗材料……………………………………………………………………19
4-2 實驗試棒之規格與準備……………………………………………………19
4-3 實驗儀器……………………………………………………………………19
4-4 實驗步驟……………………………………………………………………20
4-5 韋伯分布函數預測不同破壞機率下疲勞轉數……………………………21
第五章 結果與討論……………………………………………………………23
5-1 鋁合金7005擠製圓棒的微結構特徵…………………………………….23
5-2 拉伸試驗結果分析…………………………………………………………24
5-2-1 鋁合金7005的拉伸性質…………………………………………….24
5-2-2 鋁合金7005的拉伸破壞分析……………………………………….24
5-3 疲勞試驗結果分析…………………………………………………………26
5-3-1 鋁合金7005的疲勞性質…………………………………………….26
5-3-2 鋁合金7005的疲勞裂縫起始……………………………………….27
5-3-3 鋁合金7005的疲勞裂縫成長與破壞分析………………………….28
5-4 介在物顆粒對鋁合金7005的疲勞壽命影響…………………………….29
5-5 鋁合金7005的疲勞壽命預測…………………………………………….30
5-6 綜合討論……………………………………………………………………31
第六章 結論……………………………………………………………………33
參考文獻……………………………………………………………………………34

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