本文研究主要是討論Ti-15Mo-5Zr-3Al合金受到動態剪切荷載下之塑性變形行為，內容分為兩部分：(1)利用霍普金森扭轉試驗機，來探討Ti-15Mo-5Zr-3Al合金在高速動態剪切荷載下之塑性變形行為。其測試條件為環境溫度-150℃、25℃與300℃，剪應變速率為1200 s-1、2000 s-1與2800 s-1等三組不同的扭轉荷載速度；(2)利用霍普金森壓縮試驗機配合帽型試件，來探討Ti-15Mo-5Zr-3Al合金在極高速動態剪切荷載下之塑性變形行為。其測試條件為環境溫度25℃，剪應變速率為5×104 s-1、7×104 s-1與1×105 s-1等三組不同的壓縮荷載速度。分別討論上述兩部分實驗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Ti-15Mo-5Zr-3Al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。
在高速扭轉實驗方面，由實驗結果的數據分析中可以知道Ti-15Mo-5Zr-3Al合金機械性質受剪應變速率、溫度及剪應變量之影響甚鉅，在固定溫度條件下，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、溫度敏感性係數與微硬度皆會隨著剪應變速率的提升而增加，而活化能則隨應變速率增加而減少；另外，在固定剪應變速率條件下，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、溫度敏感性係數與微硬度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。除了數據分析之外，吾人利用掃描式電子顯微鏡(SEM)與光學顯微鏡(OM)來分別觀察破懷形貌與破壞區域之金相組織，其韌窩形貌隨應變速率與溫度的提高，有越來越密且深的趨勢；而破斷區域之金相組織隨溫度與應變速率的增加，其剪切帶區域之晶粒扭轉角與局部應變量皆增加。最後，藉由Kobayashi & Dodd模式之構成方程式能準確地描述Ti-15Mo-5Zr-3Al合金在不同溫度下的高速剪切塑變行為。
　　在極高速剪切荷載實驗方面，由實驗結果的數據分析中可以知道Ti-15Mo-5Zr-3Al合金部份的機械性質與扭轉試驗中的趨勢相同，但由於熱軟化之因素，部分機械性質需分為熱軟化前與熱軟化後來討論。應變速率敏感性係數在熱軟化前隨應變量的增加而上升，熱軟化後隨應變量的增加而下降，熱活化體積的變化趨勢則與應變速率敏感性係數相反。

　　A split-Hopkinson torsional bar system is employed to conduct a comprehensive investigation into the dynamic shear deformation behaviour and fracture characteristics of Ti-15Mo-5Zr-3Al alloy. The investigations commence by examining the mechanical response of the alloy under shear strain rates of 1200 s-1, 2000 s-1 and 2800 s-1, respectively, at temperatures of -150℃, 25℃ and 300℃. The deformation behaviour of the Ti-15Mo-5Zr-3Al alloy is then examined by performing compressive tests using hat-shaped specimens under very high strain rates of 5×104 s-1, 7×104 s-1 and 1×105 s-1, respectively, at a constant temperature of 25℃.
　　The experimental results indicate that the shear strain, shear strain rate and temperature all have a significant influence on the mechanical properties of Ti-15Mo-5Zr-3Al alloy. For a constant temperature, the flow shear stress, fracture shear strain, work hardening rate, yielding shear strength, work hardening coefficient, strain rate sensitivity, temperature sensitivity and micro-hardness all increase with increasing strain rate, while the activation energy decreases. Conversely, for a constant strain rate, the flow shear stress, work hardening rate, yielding shear strength, work hardening coefficient, strain rate sensitivity, temperature sensitivity and micro-hardness all decrease with increasing temperature, while the fracture shear strain and activation energy increase. The fracture surfaces are characterized by a dimple-like structure, which is indicative of a ductile failure mode. The appearance and density of these dimples are strongly related to the applied strain rate and temperature conditions. Optical microscopy observations reveal that the fracture surfaces are twisted into band-like features as a result of severe localized shear deformation. The width of these shear bands is determined by the strain rate and temperature applied during the deformation process. It is found that the high strain rate shear plastic behaviour of Ti-15Mo-5Zr-3Al alloy can be accurately predicted using the Kobayashi and Dodd constitutive equation.
　　In the compressive tests performed at extremely high strain rates using hat-shape specimens, the experimental results indicate that the tendencies of the rising temperature of the Ti-15Mo-5Zr-3Al alloy are broadly similar to those observed under lower strain rate conditions. However, due to softening effects, strain rate sensitivity and activation volume exhibit different characteristics before and after the point of thermal instability. For example, the strain rate sensitivity increases with increasing shear strain before the occurrence of thermal instability, but decreases with increasing shear strain thereafter. By contrast, the activation volume decreases with increasing shear strain prior to the onset of thermal instability, but then increases with increasing shear strain thereafter.

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