本文主要針對三種不同外徑/壁厚比及五種不同切痕深度6061-T6鋁合金圓管作循環彎曲負載的實驗，以探討其相關的力學行為與損壞行為。從實驗得到的彎矩-曲度關係圖顯示，在對稱循環彎曲負載時，鋁管會發生些許的循環硬化現象，並且隨著反覆的加載與卸載後，其迴圈最終會趨於穩定。此外，在同樣的外徑/壁厚比時，切痕深度對彎矩-曲度關係影響非常小。由實驗之橢圓化-曲度關係圖發現，沒有切痕的圓管呈現對稱且棘齒狀增加的變化，而有切痕的圓管隨著切痕深度越深則呈現越不對稱且棘齒狀增加的變化。且當外徑/壁厚比越大時或切痕深度越深，橢圓化-曲度曲線成長的越快且越不對稱。由實驗之控制曲度-循環至損壞圈數曲線中可看出，外徑/壁厚比和切痕深度越大時則循環至損壞圈數也就越少。最後，本文提出可描述不同外徑/壁厚比不同切痕深度圓管在循環彎曲負載時，控制曲度與循環至損壞圈數之理論方程式，在與實驗值做比較後發現，理論分析能充分的描述實驗結果。

This paper is mainly to study the response and collapse of 6061-T6 aluminum alloy tubes with three different diameter-to-thickness ratios and five different cut depths under cycling bending. The tube bending machine and curvature-ovalization measurement apparatus were used to control, measure and collect the experimental data. During the symmetrical cycling bending, it can be observed from the experimental moment-curvature curves that the loops exhibit a little bit cyclic hardening and become stable after a few bending cycles. For a certain diameter- to-thickness ratio, the cut depths have almost no influence on the moment-curvature curves. Next, from the experimental ovalization-curvature curves, the ovalization of the tube’s cross section increases in a symmetrical and ratcheting manner for tubes without a cut. However, a higher cut depth leads to a more asymmetrical ovalization- curvature curve. In addition, a larger diameter-to-thickness ratio causes a larger ovalization of the tube’s cross section. It is shown from the experimental controlled curvature-number of bending cycles required to produce failure relationships on a log- log scale that five nonparallel straight lines can be found for each diameter-to- thickness ratio. Finally, a theoretical formulation was proposed in this thesis to simulate the relationships between the 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.

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