臺灣博碩士論文加值系統

　　本文主要是利用一維彈性扭轉波傳理論為基礎的霍普金森扭轉試驗機，來探討鋁鈧合金在動態剪切荷載下之塑性變形行為。其測試條件為在-150℃、25℃與300℃環境溫度下，剪應變速率分別為800 s-1、1800 s-1與2800 s-1等三組不同的扭轉荷載速度，以研究其在動態荷載下的塑變行為與破壞特性分析，並探討兩者之相關性，同時引用一構成方程式來描述鋁鈧合金在高速剪切荷載下之塑變行為，以做為工程設計與模擬分析之用。

　　在巨觀分析中，由實驗結果可以知道，鋁鈧合金的機械性質受剪應變速率、溫度與剪應變量之影響甚鉅。在相同溫度條件下，其塑流剪應力值、破壞剪應變量、加工硬化率、降伏剪強度、加工硬化係數、應變速率敏感性係數與溫度敏感性係數皆會隨著應變速率的提升而增加，而活化能則有相反之趨勢；而在同應變速率條件下，其塑流剪應力值、加工硬化率、降伏剪強度、加工硬化係數、應變速率敏感性係數與溫度敏感性係數皆會隨著環境溫度的提高而下降，而破壞剪應變量與活化能則隨著溫度的提高而增加。

　　在微觀分析中，利用掃描式電子顯微鏡(SEM)觀察鋁鈧合金之破壞形貌，可以發現鋁鈧合金的破壞模式均屬於以韌窩為主的延性破壞，且韌窩形貌與密度會隨著應變速率與溫度的不同而有所變化。在光學顯微鏡(OM)金相組織觀察中，顯示斷口處有局部大量的剪切塑性變形，並形成一塑性流動的帶狀區域，在鋁鈧合金中僅觀察到變形式剪切帶，剪切帶的寬度亦會隨著應變速率與溫度的不同而有所變化。剪切帶中微空孔的生成與成長導致最後破壞的發生，且析出物之存在更加劇了微空孔對剪切破壞的生成。

　　最後，藉由Kobayashi & Dodd模式之構成方程式能準確地描述鋁鈧合金在不同溫度下的高速剪切塑變行為。

　The dynamic shear deformation behavior and fracture characteristics of Al-Sc alloy are studied using a split-Hopkinson torsional bar at shear strain rates of 800 s-1, 1800 s-1 and 2800 s-1 and temperatures of -150℃, 25℃ and 300℃. The experimental results indicate that shear strain, shear strain rate and temperature all have a significant influence on the mechanical properties of Al-Sc alloy. At constant temperature, the flow shear stress, fracture shear strain, work hardening rate, yielding shear strength, work hardening coefficient, strain rate sensitivity and temperature sensitivity increase with increasing strain rate, while the activation energy decreases. Under a constant strain rate, the flow shear stress, work hardening rate, yielding shear strength, work hardening coefficient, strain rate sensitivity and temperature sensitivity decrease with increasing temperature, while the fracture shear strain and activation energy increase. The fracture surfaces are characterized by dimple features, which are indicative of ductile fracture. The appearance and density of these dimples are significantly dependent on the strain rate and temperature. The fracture surfaces on the gauge length are twisted into band-like features as a result of large localized shear deformation. This phenomenon provides clear evidence of adiabatic shear bands. Only a deformed shear band is found. The width of the shear band is determined by the strain rate and temperature. It is found that microvoid nucleation and growth play a significant role in shear band formation. The presence of precipitates accelerates the adiabatic shear fracture formation via void nucleation and growth. Finally, it is shown that the Kobayashi & Dodd constitutive equation accurately describes the high-strain-rate shear plastic behavior of Al-Sc alloy under the current test conditions.

中文摘要 I
Abstract II
誌 謝 III
總目錄 IV
表目錄 VII
圖目錄 VIII
符號說明 XIII
第一章 前言 1
第二章 理論與文獻回顧 3
2-1 鋁合金之介紹 3
2-1-1 鋁合金之分類 3
2-1-2 添加合金元素對鋁之影響 3
2-1-3 鋁合金之析出硬化 4
2-2 鋁鈧合金之介紹 5
2-3 塑性變形之機械測試類別 7
2-4 一維扭轉波傳理論 8
2-5 霍普金森扭轉試驗機原理 11
2-6 材料塑性變形行為之特性 13
2-7 材料變形構成方程式 16
第三章 實驗方法與步驟 30
3-1 試件之製作 30
3-2 實驗儀器設備 31
3-2-1 霍普金森扭轉試驗機 31
3-2-2 訊號處理裝置 32
3-2-3 掃描式電子顯微鏡 (SEM) 32
3-2-4 光學顯微鏡 (OM) 33
3-2-5 微小硬度試驗機 (Micro-Hardness Tester) 33
3-3 實驗方法與步驟 33
3-3-1 動態扭轉試驗 33
3-3-2 破斷面之觀察 (SEM) 34
3-3-3 試件金相之觀察 (OM) 34
3-3-4 試件之微硬度分析 35
第四章 實驗結果與討論 40
4-1 剪應力-剪應變曲線之討論 40
4-2 加工硬化率之探討 41
4-3 應變速率效應 44
4-4 溫度效應 45
4-5 活化能 45
4-6 理論溫升量 47
4-7 材料變形構成方程式 48
4-8 微觀分析 49
4-8-1 破壞形貌觀察 (SEM) 49
4-8-1-1 試件破斷面形貌之觀察 49
4-8-1-2 試件破壞形貌之觀察 50
4-8-1-3 析出物之觀察 52
4-8-2 金相組織觀察 (OM) 53
4-8-3 剪切帶上微硬度分析 54
第五章 結論 99
參考文獻 101

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