本文主要針對五種不同深度之局部尖銳凹痕6061-T6鋁合金圓管作對稱循環彎曲負載實驗，透過彎管試驗機與曲度-橢圓化量測器，以進行實驗的測試及數據的量測，來探討其相關的力學行為與損壞。從實驗之彎矩-曲度關係圖中可知，在對稱循環彎曲負載下，實驗試件皆會產生些許循環硬化的現象，在經過反覆加載後，其迴圈會趨近於穩定的狀態，且凹痕深度對上述的關係幾乎沒有影響。其次，由橢圓化-曲度關係圖中可發現，橢圓化值會隨循環彎曲圈數的增加，曲線呈現不對稱棘齒狀的增加，且凹痕深度越深，橢圓化增加的速度就越快。由控制曲度-循環至損壞圈數雙對數關係圖中可知，凹痕深度越深，其斜率越平緩，且會為近乎平行的直線。最後，本文參考Kyriakides和Shaw【2】、Lee et al.【8】論文中所提出的理論方程式，在導入尖銳凹痕深度後，提出一個新的理論方程式，來描述不同深度局部尖銳凹痕圓管在循環彎曲負載時，控制曲度與循環至損壞圈數間的關係。此理論分析與實驗值比較後發現，理論能充分描述實驗結果。

In this thesis, the behavior and failure of local sharp-dented 6061-T6 aluminum alloy tubes with five different dent depths subjected to symmetrical cycling bending were investigated. In order to study the mechanical behavior, the tube bending machine and curvature-ovalization measurement apparatus were used to measure and collect the experimental data. From the moment- curvature relationship, it is shown that the tubes exhibit slightly cyclic hardening and become stable after a few bending cycles. The dent depth has almost no influence on its relationship. Next, for the ovalization-curvature relationship, it is shown that the curves exhibit ratcheting, unsymmetrical and increasing way along with the number of the bending cycles. Larger dent depths lead to faster increase of ovalization. From the controlled curvature-number of cycles required to produce failure relationships on a log-log scale, larger dent depths lead to flatter slopes of the relationship. In addition, the relationships almost become parallel straight lines. Finally, by referring Kyriakides and Shaw [2] and Lee et al. [8], a theoretical formulation was proposed in this thesis to simulate the relationship between the controlled curvature and number of cycles required to produce failure for local sharp- dented circular tubes with different dent depths subjected to 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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