本文實驗研究有多餘圓孔的6061-T6圓孔管在循環彎曲負載下的行為與失效，而多餘圓孔與圓孔管的圓孔直徑相同且在相同的截面上。本文考慮五種不同圓孔直徑分別為:2、4、6、8及10 mm，而五種不同角度的多餘圓孔方向分別為:45o、67.5o、90o、135o及180o。根據實驗的彎矩-曲率關係中發現，從第一循環圈數起曲線即形成一穩定的迴圈，且圓孔直徑與圓孔方向對該曲線幾乎沒有影響。而從實驗的橢圓化-曲率關係中發現，隨著循環圈數的增加，該曲線呈現不對稱、棘齒、蝴蝶結狀的增加趨勢，且圓孔直徑越大橢圓化就增加的越快。由實驗個別多餘圓孔方向的控制曲率-循環至損壞圈數雙對數座標關係中可以發現，五種不同的圓孔直徑對應出五條平行的直線，至於臨界橢圓化-控制曲率關係中可發現，越大的控制曲率將會導致越大的臨界橢圓化。最後本文提出理論來描述有多餘圓孔的6061-T6圓孔管在循環彎曲負載下的控制曲率-循環至損壞圈數的關係，並與實驗結果相互比較後可發現，理論可以合理的描述實驗結果。

This paper experimentally studies the behavior and failure of 6061-T6 round-hole tubes with redundant hole under cyclic bending. and the redundant hole have the same diameter and the same cross-section as the round holes of the round hole tube. This paper considers five different circular holes with diameters of 2, 4, 6, 8 and 10 mm, and the five different angles of redundant circular holes are 45o, 67.5o, 90o, 135o and 180o. During the symmetrical cycling bending, the moment-curvature relationship is found that the curve forms a stable loop from the first cycle, and the diameter of the hole and the direction of the hole have almost no effect on the curve. From the ovalization-curvature relationship, it is found that with the increase of the number of cycles, the curve shows an increasing trend of asymmetry, ratchet, and butterfly-shape, and the larger the diameter of the hole, the faster the ovalization increases. It is shown from the experimental controlled curvature-number of bending cycles required to produce failure relationships on a log-log scale that five different diameters of the round hole correspond to five parallel straight lines. As for the critical ovalization -control curvature relationship, it can be found that, The larger the control curvature, the larger the critical ovalization. Finally, this paper proposes a theory to describe the relationship between the control curvature of the 6061-T6 round hole tube with redundant round holes under controlled curvature and the number of bending cycles required to produce failure. By comparing the theoretical analysis with the experimental data, it is shown that the theoretical formulation can properly simulate the experimental results.
Key words: Cyclic Bending, Moment, Curvature, Ovalization, Number of Bending Cycles Required to Produce Failure, redundant hole Tubes

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