本篇研究針對不同外長軸/外短軸長度比6063-T5鋁合金橢方管在曲率控制循環彎曲負載下的力學響應和破壞模式進行了深入探討，其中橢方管有四種外長軸/外短軸長度比分別為:1.5、2.0、2.5、和3.0，而循環彎曲負載則使用五種對稱的控制曲率值分別為:±0.5、±0.55、±0.6、±0.65和±0.7 m-1。於實驗彎矩-曲率的關係中顯示，在相同的控制曲率下，彎矩的極值會隨著外長軸/外短軸長度比的增加而逐漸增加。不同的控制曲率對於彎矩-曲率在圖面上的曲線趨勢影響不大，皆會呈現出穩定的彈塑性迴圈。此外，本研究也分析外短軸變化，其定義為外短軸的長度變化量/外短軸的原始長度。於實驗外短軸變化-曲率的關係中顯示，隨著外長軸/外短軸長度比的增加，外短軸變化也會出現隨之增加的情況，四種外長軸/外短軸長度比都呈現出對稱且逐步增加的棘齒趨勢。至於控制曲率-循環至斷裂圈數的關係中顯示，在固定控制曲率的情況下，循環至斷裂圈數會隨著外長軸/外短軸長度比的增加而減少。若以雙對數座標系呈現控制曲率-循環至斷裂圈數的關係，則四種外長軸/外短軸長度比會分別對應出四條直線。最後，本研究將Shaw和Kyriakides於1987年所提出的描述光滑圓管承受循環彎曲負載下的控制曲率-循環至皺曲圈數的關係式加以修改，使其適用於描述6063-T5鋁合金橢方管的控制曲率-循環至斷裂圈數的關係。此外，本研究也提出其中相關材料參數的方程式，最終理論與實驗結果的對比顯示出高度一致性，驗證了本研究所提出的經驗公式的有效性以及實用性。

This study examines the mechanical response and failure modes of 6063-T5 aluminum alloy oval rectangular tubes with varying length ratios of the outer long axis to the outer short axis under cyclic bending loads. Tubes with length ratios of 1.5, 2.0, 2.5, and 3.0 were tested under curvature values of ±0.5, ±0.55, ±0.6, ±0.65, and ±0.7 m-1. Results showed that the maximum moment increases with the length ratio, and all moment-curvature curves exhibited stable elasto-plastic cycles regardless of curvature. The variation in the outer short axis-curvature curves displayed symmetrical and ratcheting trend. Moreover, the variation in the outer short axis increased with the length ratio. The number of cycles required to ignite fracture decreased as the length ratio increased Additionally, the controlled curvature-number of cycles required to ignite fracture showed four distinct straight lines for four length ratios on a log-log scale. This study modified the formula proposed by Shaw and Kyriakides in 1987 so that they can be used to describe the aforementioned relationships. Theoretical and experimental results were compared and found to be consistent, confirming the empirical formula’s accuracy.

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