本論文主要針對三種不同外徑/壁厚比及五種不同的凹槽深度的6061-T6鋁合金圓管進行循環彎曲負載至毀損的實驗，以探討相關呈現的行為(彎矩-曲度與橢圓化-曲度關係)與毀損(控制曲度-循環至損壞圈數關係)。從實驗彎矩-曲度曲線可以發現，在對稱控制曲度循環負載下該關係從彎曲的第一圈起，便形成一個穩定的迴圈。當外徑/壁厚比越大時，鋁管壁厚就越薄，彎矩-曲度迴圈會較小。此外，由於凹槽是局部且微小，所以凹槽深度對彎矩-曲度關係並沒有太大的影響。由實驗橢圓化-曲度關係可以觀察到，當鋁管沒有凹槽時曲線會呈現棘齒狀對稱的成長，而當鋁管有凹槽時曲線會呈現棘齒狀不對稱的成長，且外徑/壁厚比越大或凹槽深度越深時，曲線會越不對稱且橢圓化成長也越快。另外，由實驗控制曲度-循環至損壞圈數關係中可看出，當外徑/壁厚比越大或凹槽深度越深時，由於橢圓化成長的增加，鋁管的循環至損壞圈數就越少。最後，本文提出相關的理論模式來描述循環彎曲負載下控制曲度與循環至損壞圈數的關係。實驗和理論的結果比較後發現，理論模擬能合理的描述實驗結果。

This thesis is mainly to study the behavior (the relationship of moment, ovalization and curvature) and failure (the relationship of controlled curvature and number of cycles to ignite failure) of 6061-T6 aluminum alloy tubes with five different sharped-notched depths and three different diameter-to-thickness ratios under cyclic bending. During the symmetrical cyclic bending, it can be observed from the experimental moment-curvature curves that the loops become stable at the first bending cycle. When the diameter-to-thickness ratio is getting bigger, the aluminum alloy tube becomes thinner and the moment-curvature loop becomes smaller. Additionally, the sharp-notched is local and tiny, there is no influence on the relationship of moment-curvature when the depth of sharp-notched changes. Next, from the experimental ovalization-curvature curves, the ovalization of the tube’s cross-section increases in a ratcheting and symmetrical manner for tubes without any notch. When the sharp-notched depth is higher, the ovalization-curvature curves become more asymmetrical. In addition, a larger diameter-to-thickness ratio causes a larger ovalization of the tube’s cross section. Moreover, From the relationship of the controlled curvature and number of cycles to ignite failure, the diameter-to-thickness ratio is higher, the number of cycles to ignite failure becomes lower. Finally, a theoretical model was purposed in this paper to describe the relationships between the controlled curvature and the number of bending cycles to failure. After comparing with the experimental data, the theoretical model can properly describe the experimental results.

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