本文主要是實驗研究不同圓孔方向與不同圓孔直徑的6061-T6鋁合金圓孔管在不同曲率比（最小曲率/最大曲率）循環彎曲負載下的力學行為和失效損壞，其中以彎矩-曲率和橢圓化-曲率的關係來呈現力學行為，以控制曲率範圍-循環至損壞圈數的關係來呈現失效損壞。本研究不同的圓孔方向有:0°、30°、60°與90°，不同的圓孔直徑有:2、4、6、8與10 mm，而不同的曲率比有:-1、-0.5、0與0.5。根據實驗結果顯示，不同圓孔方向或不同圓孔直徑對於彎曲-曲率的關係幾乎沒有影響，但對橢圓化-曲率的關係則有顯著的影響。當曲率比= -1時，彎曲-曲率的關係從第一個循環圈數開始便呈現為一個彈-塑性且穩定的迴圈，而橢圓化-曲率的關係則是呈現不對稱、增長、蝴蝶結狀的趨勢。當曲率比= -0.5、0與0.5時，因為曲率範圍變小的因素，導致彎矩對曲率的關係從第二個循環圈數起便呈現為一個線彈性的路徑，且隨著循環圈數的增加，路徑會有些許鬆弛但之後很快又會回到一個穩定的狀態。由於變形都是在彈性範圍內發生，使得橢圓化的增長呈現十分的緩慢。另外，當固定圓孔方向時，各個圓孔直徑的四種不同曲率比曲率範圍-循環至損壞圈數雙對數座標關係呈現出四條幾乎相互平行的直線。最後，本文使用Lee等人於2021年所提出理論來描述不同圓孔方向與不同圓孔直徑的6061-T6鋁合金圓孔管在不同曲率比循環彎曲負載下曲率範圍-循環至損壞圈數的關係，其中的材料參數將導入不同圓孔方向的變數，在與實驗結果進行比較後發現，理論可合理的描述實驗結果。

This paper mainly studies the mechanical behavior and failure of 6061-T6 aluminum alloy round-hole tubes with different hole directions and different hole diameters under cyclic bending with different curvature ratios. The different hole directions in this study are: 0°, 30°, 60° and 90°, the different hole diameters are: 2, 4, 6, 8 and 10 mm, and the different curvature ratios are: -1, -0.5, 0 and 0.5. According to the experimental results, different hole directions or different hole diameters have little effect on the moment-curvature relationship but have a significant impact on the ovalization-curvature relationship. When the curvature ratio = -1, the moment-curvature relationship presents an elastic-plastic and stable loop from the first cycle, while the ovalization-curvature relationship is asymmetrical, growing, bow tie like trend. When the curvature ratio = -0.5, 0 and 0.5, due to the smaller curvature range, the relationship between the moment and the curvature presents a linear elastic path from the second cycle, and with the number of cycles increases, the path relaxes a little but quickly returns to a stable state. Since the deformation occurs in the elastic range, the growth of ovalization is very slow. In addition, when the direction of the circular hole is fixed, the relationship between the four different curvature ratios of the diameters of each diameter and the double logarithmic coordinate relationship between the range of curvature and the number of cycles to failure presents four almost parallel lines. Finally, the theory proposed by Lee et al. in 2021 is used to describe the relationship between the curvature range and the number of cycles to failure of 6061-T6 aluminum alloy round-hole tubes with different hole directions and different hole diameters under cyclic bending with different curvature ratios. Then the theoretical material parameters will be introduced into the variables of different hole directions. After comparing with the experimental results, it is found that the theory can reasonably describe the experimental results.

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