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(Split Hopkinson Torsional Bar)，來探討鈦合金(Ti-6Al-4V)在動態剪切荷載下塑變行為。其測試條件為在-100℃、-50℃、25℃及300℃環境溫度下，剪應變速率分別為1800s-1、2300s-1、及2800s-1等三組不同的扭轉荷載速度，以研究其在動態扭轉荷載下的塑變行為與破壞特性分析，並探討不同環境溫度下對材料的相關性，同時引用一構成方程式來描述Ti-6Al-4V在高速剪切荷載下的塑變行為，以作為工程設計與模擬分析時的參考依據。
實驗結果顯示，溫度及應變速率對Ti-6Al-4V之機械性質影響顯著，其塑流應力值在固定應變量下隨著應變速率的提升與在固定應變速率下隨著溫度的下降而增加，並可由Kobayashi & Dodd模式準確地描述Ti-6Al-4V合金的在不同溫度下的高速剪切塑變行為。此外，應變速率的提升與溫度的下降亦導致材料之加工硬化率、應變速率敏感性及昇溫量的上升，但熱活化體積卻會隨著應變速率提升而下降。從掃描式電子顯微鏡的破壞形貌分析中，可發現Ti-6Al-4V的破壞模式均屬於以韌窩為主的延性破壞，其斷面涵括密集韌窩區與平滑區兩特徵區域。此兩特徵區域形貌亦隨著應變速率之變化而異，並且在平滑區可發現局部融熔的瘤狀物形貌。由光學顯微鏡的顯微組織之觀察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。在溫度25℃與300℃下，係以變形剪切帶形式出現，但在-50℃與-100℃下則是呈現相變態之剪切帶。在剪切帶中微裂縫的的生成與結合導致最後的破壞發生。

The dynamic shear deformation behavior and fracture characteristics of Ti-6Al-4V alloy are studied by torsional split-Hopkinson bar at temperature ranging from -100℃ to 300℃ under three strain rates ( 1800 s-1, 2300 s-1, 2800 s-1). The effects of strain rat and temperature on the mechanical response and microstructure of the alloy are evaluated. At constant temperature, flow stress, work hardening rate coefficient and strain rate sensitivity increase with increasing strain rate, but activation volume decreases. Under constant strain rate, flow stress, work hardening rate coefficient, strain rate sensitivity and temperature sensitivity decrease with increasing temperature, but activation volume increases. Furthermore, the activation energy, DG*, is found to attain a maximum value of 15 KJ/mole for the current tests. We also find dimple characteristics on fracture surfaces and divide the fracture surface appearance into two characteristic zones; the densely dimpled and the smooth surfaced zones. The two characteristic zones have significant difference with increasing strain rate and temperature. Two kinds of shear band, transformed shear band and deformed shear band are found at sub-zero temperature and above room temperature, relatively. This results indicate that microvoid nucleation and growth playing an important role in the shear band deformation. The Kobayashi & Dodd constitutive equation accurately describes the flow behavior of Ti-6Al-4V alloy for the test conditions.

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