本論文主要探討6061-T6鋁合金圓管於不同角度銲接下，在循環彎曲負載作用時的行為。研究係透過不同的控制曲率循環彎曲負載，分析不同銲接角度對循環至損壞圈數之影響，並進一步建立控制曲率、銲接角度與循環至損壞圈數之間的關聯。本實驗的圓管外徑為35 mm、壁厚為3 mm，並以圓管長軸平行水泥台設定為0°基準角度，分別製作45°、60°及90°三種銲接角度之試件。經由不同的控制曲率進行循環彎曲試驗，觀察銲接角度變化對循環至損壞圈數之影響。
實驗結果顯示，在固定彎曲方向的情況下，控制曲率越大時，試件達到損壞的循環次數就越少。此外，在相同控制曲率下，銲接角度與水泥平台呈90°時，循環至損壞圈數最長；相反地，當銲接角度越接近水泥平台方向時，循環至損壞圈數則越短。本研究將上述控制曲率-循環至損壞圈數的實驗數據繪製於雙對數座標後可觀察到，該關係在各銲接角度的皆呈現線性分布。本研究最終建立了一套描述不同銲接角度6061-T6鋁合金圓管在循環彎曲負載下，控制曲率-循環至損壞圈數的理論模式。理論分析與試驗結果比較後顯示兩者高度一致，證實本研究所建立的理論模式能有效描述實驗結果。

This thesis primarily investigates the behavior of 6061-T6 aluminum alloy circular tubes with different welding angles under cyclic bending loads. Using cyclic bending tests with various controlled curvature levels, the effects of welding angle on the number of cycles to failure were analyzed, and the relationship among controlled curvature, welding angle, and cycles to failure was further established. The test specimens were circular tubes with an outer diameter of 35 mm and a wall thickness of 3 mm. Taking the tube longitudinal axis parallel to the concrete platform as the 0° reference, specimens with welding angles of 45°, 60°, and 90° were fabricated. Cyclic bending tests under different controlled curvature levels were conducted to observe the influence of welding angle on the number of cycles to failure.
The experimental results indicate that, for a fixed bending direction, a larger controlled curvature leads to fewer cycles to failure. Moreover, under the same controlled curvature, specimens with a welding angle of 90° relative to the concrete platform exhibited the longest fatigue life, whereas specimens with welding angles closer to the platform direction showed shorter cycles to failure. When the experimental data of controlled curvature versus cycles to failure were plotted on double-logarithmic coordinates, a linear relationship was observed for all welding angles. Based on these findings, this study established a theoretical model describing the relationship between controlled curvature and cycles to failure for 6061-T6 aluminum alloy circular tubes with different welding angles under cyclic bending loads. Comparison between the theoretical predictions and experimental results shows a high degree of agreement, confirming that the proposed theoretical model can effectively describe the experimental behavior.

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