本文主要針對兩種不同外徑/壁厚比及五種不同凹痕深度之6061-T6鋁合金圓管試件做對稱循環彎曲負載實驗，以探討其相關力學行為與損壞關係。從實驗彎矩-曲度關係圖中顯示，在對稱循環彎曲負載時，實驗試件皆會發生些許循環硬化現象，隨著反覆的加載與卸載後，其迴圈最終會趨於穩定。當外徑/壁厚比或凹痕深度越大時，彎矩-曲度關係會呈現不對稱的趨勢。其次，由實驗之橢圓化-曲度曲線中發現，沒有凹痕的圓管呈現對稱且棘齒狀增加的變化，而有凹痕的圓管則呈現不對稱且棘齒狀增加的變化。當外徑/壁厚比或凹痕深度越大時，橢圓化-曲度曲線成長得越快且越不對稱。由實驗之控制曲度-循環至損壞圈數曲線中可看出，控制曲度越大則循環至損壞圈數就越少、外徑/壁厚比或凹痕深度越大時則循環至損壞圈數就越少。由控制曲度-循環至損壞圈數雙對數座標關係圖中發現，個別外徑/壁厚比的五種不同凹痕深度呈現五條不平行的直線。本文最後參考吳政昌【21】論文中所提出的理論模型，並導入不同外徑/壁厚比後，提出一個可描述不同外徑/壁厚比不同深度凹痕圓管在循環彎曲負載時控制曲度與循環至損壞圈數關係。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。

In this thesis, the mechanical response and collapse of 6061-T6 aluminum alloy circular tubes with two different diameter-to-thickness ratios and five different dent depths under cyclic bending were investigated. From the experimental moment-curvature relationships under symmetrical cyclic bending, they exhibit a relatively small cyclic hardening and become stable after a few loading and reloading cyclic processes. Larger diameter-to-thickness ratios or dent depths lead to unsymmetrical trend of the moment- curvature relationship. Next, From the experimental ovalization-curvature relationships, they exhibit symmetrical and ratcheting increase for circular tubes without a dent. However, they exhibit unsymmetrical and ratcheting increase for circular tubes with a dent. Larger diameter-to-thickness ratios or dent depths lead to fast increase and sever unsymmetry of the ovalization-curvature relationships. From the experimental controlled curvature-number of cycles required to produce failure relationship, higher controlled curvatures lead to lower number of cycles required to produce failure and larger diameter-to-thickness ratios or dent depths lead to lower number of cycles required to produce failure. From the experimental controlled curvature-number of cycles required to produce failure relationship in a log-log scale, five unparallel straight lines can be observed for each diameter-to-thickness ratio. By referring the theoretical model proposed by Wu【21】and importing the diameter-to-thickness ratio, a model was proposed to describe the controlled curvature-number of cycles required to produce failure relationship for round-dented circular tubes with different diameter-to-thickness ratios and different dent depths under cyclic bending. 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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