本文係研究不同圓孔方向與不同圓孔直徑的6061-T6鋁合金圓孔管在循環彎曲負載下的橢圓化成長與臨界橢圓化，其中不同的圓孔方向有:0、30、60與90，而不同的圓孔直徑有:2、4、6、8與10 mm。本文選用6061-T6鋁合金圓孔管在不同控制曲率下進行循環彎曲至損壞的實驗，而在實驗過程中會量測曲率、橢圓化與循環圈數。根據實驗結果顯示，橢圓化成長與循環圈數的曲線大略可分成三個階段：初始階段、第二階段與第三階段，而大多的循環圈數都在初始階段與第二階段。最後，當裂痕出現時，橢圓化成長進入第三階段並急遽的上升，最後導致6061-T6鋁合金圓孔管的斷裂。接著，本文採用Lee等人[11]所提出的關係式，並將圓孔方向與圓孔直徑變數導入相關的材料參數中，則該關係式可用來描述初始階段與第二階段的橢圓化-循環圈數關係。此外，本文採用胡庭源[15]所提出的關係式，並將圓孔方向與圓孔直徑變數導入相關的材料參數中，則該關係式可用來描述臨界橢圓化-控制曲率的關係。經由理論分析與實驗結果相互比較後發現，理論可合理描述實驗結果。

This thesis studies the ovalization growth and critical ovalization of 6061-T6 aluminum alloy round-hole with different hole directions and different hole diameters under cyclic bending loads. The different hole directions include 0, 30, 60 and 90, and different hole diameters include 2, 4, 6, 8 and 10 mm. During the cyclic bending experiment, the curvature, ovalization, and the number of cycles needed to ignite failure are recorded. According to the experimental results, it shows that the ovalization - number of cycles relationship can be roughly divided into three stages, the initial, the second and the third stages. However, most of the bending cycles are in the initial and the second stages. When the ovalization enters the third stage, the ovalization increases sharply, which leads to the fracture of the 6061-T6 aluminum round-hole tube. In this study, the empirical formulation proposed by Lee et al. [11] was used. In addition, the variable of the hole directions was induced into the relevant material parameters. Therefore, the modified formulation can be used to describe the ovalization - number of cycles relationship for the initial and second stages. Finally, the empirical formulation proposed by Hu [15] is adopted. In addition, the variable of the hole directions was induced into the relevant material parameters. Therefore, the modified formulation can be used to describe the critical ovalization-controlled curvature relationships. After comparing the theoretical analysis with the experimental results, it is found that the theory can reasonably describe the experimental results.

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