臺灣博碩士論文加值系統

本文利用一維波傳理論為基礎的霍普金森動態試驗機來探討高錳鋼在不同應變速率下的動態塑性變形行為。其測試溫度為25℃，應變速率條件分別為1980 s-1，2950s-1，4330 s-1，4900 s-1，6200 s-1，8300 s-1六組不同的荷載速度，以研究高錳鋼在動態荷載下應變速率對其機械性質的影響，並藉由OM、SEM及TEM顯微組織的觀察，來探討巨觀機械性質及微觀組織結構兩者之間的相關性，並引入一構成方程式，用來描述材料在高速動態的塑性變形行為，以作為設計與應用之依據。
由實驗數據之分析顯示，高錳鋼之機械性質受到應變速率和應變量的影響甚大。其塑流應力隨著應變速率的上升而明顯地增加。且發現高錳鋼具有極高的加工硬化速率，其加工硬化速率隨著應變速率的上升而上升，代表著愈高的應變速率下，其加工硬化效應愈明顯。另外，應變速率敏感性值隨著應變量和應變速率的上升而上升，同時與加工硬化應力( )呈線性增加的關係，然而相對於熱活化體積的變化卻有著相反的趨勢。在破壞特徵分析上，發現高錳鋼的破壞模式是由晶界微裂縫的形成及絕熱剪切帶所主宰，且微裂縫數目隨應變速率上升而上升，並導致破壞應變量的減少，同時發現脆性之平面破壞區隨應變速率的上升而增加。經由TEM微觀組織的觀察發現，在固定的應變下，差排密度隨著應變速率上升而快速增殖，並導致差排胞尺寸急遽的下降，進而影響塑流應力之趨勢，在高速荷載條件下，皆可發現雙晶的形成，且雙晶的數量因高應變速率之溫升效應，而隨著應變速率上升而下降。同時利用Campbell構成方程式，可以準確描述高錳鋼的動態塑性變形行為，以供分析與模擬所需。

The purpose of the study is to investigate the deformation behavior of high Mn steel (Hadfield Steel) under high strain rate loading conditions. The mechanical testing is performed in the strain rates 1980s-1、2950 s-1、4330 s-1、4900 s-1、6200 s-1 and 8300 s-1, respectively and at room temperature by using Split-Hopkinson Bar tester which is developed based one dimensional elastic wave propagation theory. The O.M.、S.E.M. and T.E.M. techniques are also used to analyze the fracture and microstructure characteristics of the deformed specimen. With the macroscopic and microscopic results, a constitutive equation is used to describe the plastic deformation behavior of the material.
The experimental results indicates that strain rate strongly influence the mechanical properties of high Mn steel. Flow stress and work hardening rate increase with strain rate. The strain rate sensitivity also increase with strain rate, but the inverse tendency is observed for the activation volume. The failure analysis shows that the fracture is dominated by the form of microcrack in the grain boundary and adiabatic shear band. The number of microcrack increase with strain rate and lead to the fracture strain decrease. Microstructural observations reveals that the morphologies and characteristic of dislocation are sensitive to the loading rate. At high strain rate and large deformation, great dislocation density are observed. On high loading condition, the twin is observed. And the number of twin is decreased with increasing strain rate due to the rising temperature. Finally, the Campbell constitutive equation is used to describe the high-strain-rate plastic deformation of high Mn steel.

中 文 摘 要I
ABSTRACTII
誌 謝III
總目錄IV
表目錄VII
圖目錄VIII
符號說明XI
第一章 前言1
第二章 理論與文獻回顧3
2-1 一維波傳理論3
2-2 霍普金森桿原理6
2-3材料塑性變形行為之特性8
2-4塑性變形之機械測試類別11
2-5圓柱壓縮試驗法13
2-6材料變形構成方程式13
第三章 實驗方法與步驟22
3-1試件之準備22
3-2實驗設備22
3-2-1霍普金森動態撞擊試驗機22
3-2-2訊號處理裝置23
3-2-3壓縮試驗機24
3-2-4光學顯微鏡(OM)24
3-2-5掃瞄式電子顯微鏡(SEM)24
3-2-6穿透式電子顯微鏡(TEM)24
3-2-7雙噴射式電解拋光機25
3-3實驗方法與步驟25
3-3-1動態衝擊實驗25
3-3-2壓縮試驗26
3-3-3試件金相之觀察(OM)27
3-3-4破斷面之觀察(SEM)27
3-3-5穿透式電子顯微鏡(TEM)27
第四章 實驗結果與討論31
4-1 應力-應變曲線圖之討論31
4-2應變速率效應32
4-3 熱活化體積33
4-4 理論昇溫量之探討34
4-5材料變形構成方程式35
4-6微觀組織36
4-6-1破壞特徵分析36
4-6-2 TEM顯微結構分析38
第五章 結論69
參考文獻71
自 述80

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