本文係實驗探討不同長/短軸長度比橢圓形管在循環彎曲負載下響應與失效，其中所採用橢圓形管材料為SUS304不鏽鋼，而四組不同的長/短軸長度比分別為:1.5、2.0、2.5和3.0，橢圓形管的管壁厚度皆為0.7 mm，並以不同對稱曲率控制進行循環彎曲負載至皺曲失效的實驗，至於彎矩的方向則與長軸方向重疊。根據實驗結果顯示，不論長/短軸長度比，彎矩-曲率的關係會呈現循環硬化後，即形成一穩定的彈塑性迴圈，在相同的控制曲率情況下，隨著長/短軸長度比的增加，彎矩的極值會有些許的下降，但變化不大。接著，本文以短軸變化取代橢圓化，其定義為短軸變化量/原始短軸長。實驗結果顯示，長/短軸長度比為1.5時，短軸變化-曲率關係會隨著循環圈數的增加呈現對稱、增加與棘齒狀的趨勢，但是當長/短軸長度比為2.0以上時，則該關係會隨著循環圈數的增加而呈現對稱、增加與蝴蝶狀的趨勢，且長/短軸長度比越大時，短軸變化就越大。此外，若以雙對數座標表示曲率-循環至皺曲圈數關係，則四組長/短軸長度比可以對應出四條直線。最後，本文將Kyriakides和Shaw[2]所提出的相關經驗公式修改後，來描述不同長/短軸長度比的SUS304不鏽鋼橢圓形管承受循環彎曲負載下的曲率-循環至皺曲圈數關係。經由理論描述與實驗數據的比較結果顯示，本文所提出的經驗公式可合理地描述實驗結果。

This paper investigates the response and failure of elliptical tubes with different major/minor axis length ratios under cyclic bending. SUS304 stainless steel is used as the material for the elliptical tubes with four major/minor axis length ratios of 1.5, 2.0, 2.5, and 3.0. The wall thickness is 0.7 mm, and cyclic bending loads are applied until buckling failure. The experimental moment-curvature relationships show cyclic hardening and become a stable loop for all major/minor axis length ratios. Increasing major/minor axis length ratio slightly decreases the peak bending moment. This study also explores the minor axis variation-curvature relationships (minor axis variation = change of the length of the minor axis / original length of the minor axis), a symmetrical, ratcheting, and increasing trend with an increase in the number of cycles is found for major/minor axis length ratio = 1.5. However, when the major/minor axis length ratio = 2.0, 2.5, and 3.0, the relationships exhibits a symmetrical, ratcheting, increasing and butterfly-like trend with an increase in the number of cycles, and the minor axis variation increases with a larger major/minor axis length ratio.
For the curvature-number of cycles needed to initiate buckling relationships, it can be observed that a larger major/minor axis length ratio causes a fewer number of cycles needed to initiate buckling. In addition, four major/minor axis length ratios correspond to four straight line lines for the curvature-number of cycles needed to initiate buckling relationships in double logarithmic coordinates. Finally, this study used theoretical equations to describe the above-mentioned relationships. The theoretical analysis was compared with experimental data, and it was found that both approaches were very close, indicating that the theory could reasonably describe the experimental results.

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