為模擬摩擦攪拌焊接過程預熱階段的溫度分佈歷程和材料塑性流動，本研究使用牛頓-瑞弗生法，聯立求解圓柱座標系之能量與動量守恆方程式。藉由數值模擬與實驗結果比較，結果發現鋁合金6061-T6在摩擦攪拌焊接的預熱階段初期，工件材料與刀具接觸面為純摩擦且無材料之塑性流動，材料之熱源為界面間的摩擦熱。當溫升至300度C以上 (工件厚度一半處，約1.5mm) 材料開始產生塑性流動，其產熱功率會急遽升高，又隨溫度之快速升高而功率下降並逐漸趨於穩定值。材料受熱膨脹也會導致界面下壓力增加而使產熱功率增加，因此溫度隨之升高。達穩態時之黏著比越大會使功率與溫度更快趨於飽和。

數值模擬顯示當材料流動達到穩態時，刀具轉速越高材料流動速度與剪應變率越高。接觸條件因子的調控能有效表達不同接觸狀態下的產熱功率與塑性流動的流速分佈，並透過實驗紀錄與數值結果作比較，可以估計界面的接觸狀態或黏著與滑動比例。

In order to simulate the histories of temperature distributions and plastic flow of the dwell phase during a friction stir welding process, the Newton-Raphson method is used to solve the simultaneous equations of energy and momentum in the cylindrical-coordinate system. Comparing the simulation with the results of experiment, results show that the contact condition between the tool and the workpiece is at pure sliding without plastic flow at the beginning of the dwell phase until the temperature rises to about 300°C at the depth of 1.5 mm. In this period, the heat generation comes from the sliding friction between two surfaces. After the plastic flow occurs, the heat generation rises rapidly, and then decreases to a saturated value so that the temperature rise also achieves a constant value. Thermal expansion of the workpiece will increase the plunge force, so that the heat generation and the temperature raise increase. At the steady state condition, with increasing sticking proportion, the heat generation and the temperature quickly achieve a saturated value.

For the steady-state condition, results show that the speed of plastic flow and shear strain rate increase with increasing rotational speed. The control of the contact state variable can effectively describe the heat generation and the distribution of plastic flow in different contact conditions. Comparing the simulation with the results of experiment, the contact condition can be identified.

封面 i
論文審定書 ii
中文摘要 iii
英文摘要 iv
目錄 vi
圖次 viii
表次 x
符號說明 xi

第一章 緒論 1
1.1 摩擦攪拌焊接簡介 1
1.2 文獻回顧 2
1.3 研究目的和方法 4
1.4 論文架構 4
第二章 數值模型 6
2.1 材料塑性流動模型 7
2.2 熱傳模型 13
2.3 邊界條件的設定 14
2.4 數值方法 18
第三章 結果與討論 22
3.1 穩態時接觸條件因子對材料塑性流動之影響 22
3.2 導熱係數、刀具下壓力與刀具轉速對溫度變化的影響 27
3.3 溫度分佈歷程與實驗量測結果比較 31
3.4 接觸狀態之推測 37
第四章 結論 41
參考文獻 42

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