本文係研究6061-T6鋁合金圓孔管在循環彎曲下的橢圓化成長與臨界橢圓化，研究採用五種不同圓孔直徑(2、4、6、8與10 mm)在不同的曲率控制循環彎曲負載，量測橢圓化成長變化並找出橢圓化與循環圈數的關係。實驗結果顯示，橢圓化與循環圈數的曲線大致可分成三個階段，初始階段、第二階段和第三階段，且橢圓化成長幾乎都在初始階段和第二階段，在第三階段橢圓化會急遽的上升，隨之而來的是圓孔管的斷裂。由於橢圓化與循環圈數曲線的趨勢與2016年Lee et al. [8]所研究環圓周尖銳凹槽的6061-T6鋁合金的橢圓化與循環圈數曲線非常相似，所以本文修改相關的理論來描述不同圓孔直徑的6061-T6鋁合金圓孔管在不同曲率控制循環彎曲下初始及第二階段橢圓化與循環圈數的關係。此外，根據實驗的結果，本文也提出理論來描述不同圓孔直徑的6061-T6鋁合金圓孔管在不同曲率控制循環彎曲下臨界橢圓化與控制曲率的關係，理論分析與實驗結果相比較後發現，理論可合理描述實驗結果。

This paper studies the ovalization growth and critical ovalization of 6061-T6 aluminum alloy round-hole tubes subjected to cyclic bending. This paper uses the round-hole tubes with five different diameters of the round hole (2, 4, 6, 8, and 10 mm) subjected to cyclic bending at different curvatures for measuring the ovalization, the number of bending cycles and the critical ovalization. The experimental result shows that the curve of the ovalization and the number of cycles can be divided into three stages, the initial, second and third stages. The trend of this curve was similar to that of sharp-notched 304 stainless steel tubes tested by Lee et al. [8], thus, the empirical formulation proposed by them was used for simulating the aforementioned relationship in the initial and second stages. In addition, a theoretical formula was also proposed to simulate of the relationship between the critical ovalization and controlled curvature. The simulation results were compared with the experimental results, and it was found that the theoretical analysis could reasonably reproduce the experimental results.

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