本研究針對不同外長軸/外短軸長度比的304不鏽鋼橢圓管在不同曲率比循環彎曲負載下的失效與響應進行實驗研究，其中不同的外長軸/外短軸長度比分別為：1.5、2.0、2.5與3.0，所探討的曲率比為：-1、-0.5與0，而曲率比的定義為:最小控制曲率除以最大控制曲率。循環彎曲負載下響應有:彎矩-曲率與短軸變化-曲率之關係，而循環彎曲負載下的失效為曲率範圍-循環至破壞圈數之關係。
實驗結果顯示，彎矩-曲率圖在曲率比為-1、-0.5以及0時，皆會隨循環圈數增加而形成穩定的彈塑性迴圈，當曲率比為-0.5與0時，彎矩-曲率迴圈會呈現些許循環鬆弛的現象，在相同的曲率比下的外長軸/外短軸長度比越大，其彎矩的最大值會略為減少。由短軸變化-曲率圖可知，其變化量皆隨循環圈數穩定上升，當外長軸/外短軸長度比為1.5時，短軸變化與曲率的關係會呈現棘齒狀，當外長軸/外短軸長度比為2.0、2.5、3.0時，短軸變化與曲率的關係會則會呈現類似蝴蝶狀，當曲率比為-1時，短軸變化量與曲率的關係曲線呈現對稱，當曲率比為-0.5以及0時，短軸變化量與曲率的關係曲線則呈現非對稱，且偏向平均曲率值的方向。在相同的曲率比下的外長軸/外短軸比越大，短軸變化量之上升幅度越大。至於在循環至破壞圈數方面，當外長軸/外短軸比固定時，循環至破壞圈數會隨曲率範圍增加而減少；當曲率範圍固定時，外長軸/外短軸長度比越大則循環至破壞圈數越少；曲率比越接近-1，循環至破壞圈數越大。此外，曲率範圍-循環至破壞圈數關係圖以雙對數座標表示時，原本的曲線皆轉化為不同斜率的直線，最後本研究針對曲率範圍與循環至破壞圈數之間的關係進行理論分析，並與實驗結果進行比對，結果顯示兩者高度一致，驗證了理論模型的準確性。

This study experimentally investigates the failure behavior and structural response of SUS304 stainless steel elliptical tubes with various ratios of outer major axis to outer minor axis under cyclic bending loads with different curvature ratios. The examined axis ratios are 1.5, 2.0, 2.5, and 3.0, while the curvature ratios considered are −1, −0.5, and 0. The curvature ratio is defined as the minimum controlled curvature divided by the maximum controlled curvature. The observed responses under cyclic bending include the moment–curvature relationship and the variation of the minor axis versus curvature. Failure under cyclic bending is evaluated through the relationship between curvature range and the number of cycles to failure.
Experimental results show that the moment–curvature curves form stable elastoplastic hysteresis loops with increasing cycle count for all curvature ratios of −1, −0.5, and 0. At curvature ratios of −0.5 and 0, a slight cyclic relaxation phenomenon is observed in the hysteresis loops. Under a constant curvature ratio, an increase in the major-to-minor axis ratio results in a slight decrease in the peak moment. The minor axis variation–curvature curves exhibit a steadily increasing trend with cycle number. When the axis ratio is 1.5, the curve shows a serrated pattern, whereas axis ratios of 2.0, 2.5, and 3.0 yield butterfly-shaped curves. For a curvature ratio of −1, the minor axis variation curve is symmetric, while for −0.5 and 0, the curves are asymmetric and skewed toward the direction of the mean curvature.
At the same curvature ratio, the amplitude of minor axis variation increases with larger axis ratios. In terms of the number of cycles to failure, under a fixed axis ratio, increasing the curvature range reduces the number of cycles to failure. Conversely, under a fixed curvature range, higher axis ratios result in fewer cycles to failure. In addition, the closer the curvature ratio is to −1, the greater the number of cycles to failure. When plotted on a log–log scale, the curvature range versus number of cycles to failure relationship transforms from a curve into straight lines with varying slopes. Finally, a theoretical analysis of the relationship between curvature range and number of cycles to failure is conducted and compared with the experimental data. The results demonstrate strong agreement, confirming the accuracy of the proposed theoretical model

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