本論文主要是探討不同方向與不同長/短軸長度比的SUS 304不鏽鋼橢圓管在對稱控制曲率循環彎曲負載下的響應與失效，其中以彎矩-曲率關係與短軸變化(短軸變化量/原始短軸長度)-曲率關係來呈現響應，而以控制曲率-循環至皺曲圈數關係來呈現失效。本研究不同方向 (長軸方向與彎矩方向的夾角)有：0º、30º、60º和90º，而不同長/短軸長度比有：30 mm/20 mm = 1.5、40 mm/20 mm = 2.0、50 mm/20 mm = 2.5和60 mm/20 mm = 3.0，至於橢圓管的壁厚皆為0.7 mm。
根據實驗結果顯示，從彎矩-曲率關係中發現，在初始有循環硬化的現象後，即形成一個穩定的彈塑性迴圈，且曲率越大彎矩值就越大。當固定方向時，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；而當固定長/短軸長度比時，方向越大彎矩值就越大。接著，從短軸變化-曲率關係中發現，當固定方向時，長/短軸長度比為1.5，短軸變化-曲率關係會隨著循環圈數的增加呈現對稱、棘齒與增加的趨勢，但是當長/短軸長度比為2.0、2.5與3.0時，則該關係會隨著循環圈數的增加而呈現對稱、棘齒化與增加的蝴蝶狀趨勢，且長/短軸長度比越大時，短軸變化就越大。此外，當固定長/短軸長度比時，方向角度越大時，短軸變化就越慢且越小。至於控制曲率-循環至皺曲圈數關係則呈現，當長/短軸長度比越大時循環至皺曲圈數就越小；當方向越大時循環至皺曲圈數就越大。另外，控制曲率-循環至皺曲圈數關係在雙對數座標關係圖中可以發現，在同一長/短軸長度比下，四種不同方向會呈現出四條近乎平行的直線。最後，本文統整出理論方程式來描述不同方向與不同長/短軸長度比的SUS 304不鏽鋼橢圓管在對稱曲率控制循環彎曲負載下的控制曲率-循環至皺曲圈數關係，並且將理論分析與實驗結果比較後發現，在雙對數座標中兩者數據非常接近，表示理論能夠合理的描述實驗結果。

This paper primarily investigates the response and failure of SUS 304 stainless steel elliptical tubes with different directions and different major/minor axis length ratios under symmetric controlled cyclic bending loads. The response is presented in terms of the moment-curvature relationship and the minor axis variation (variation in the minor axis length/original minor axis length)-curvature relationship. The failure is presented in terms of the controlled curvature-number of cycles needed to initiate buckling relationship. In this study, different directions (angles between the major axis direction and the applied moment direction) are considered: 0°, 30°, 60°, and 90°. Additionally, different major/minor axis length ratios are investigated: 30mm/20mm = 1.5, 40mm/20mm = 2.0, 50mm/20mm = 2.5, and 60mm/20mm = 3.0. According to the experimental results, it was observed from the moment-curvature relationship that after the initial cyclic hardening, a stable elastic-plastic loop was found, and the moment value increased with a larger curvature. When the direction was fixed, under the same controlled curvature conditions, the maximum moment decreased slightly with an increase in the major/minor axis length ratio, but the change was not significant. However, when the major/minor axis length ratio was fixed, the moment value increased with a larger direction. Next, from the minor axis variation-curvature relationship, it was found that when the direction was fixed and the major/minor axis length ratio = 1.5, the minor axis variation-curvature relationship showed a symmetrical, ratcheting, and increasing trend with an increase in the number of cycles. However, when the major/minor axis length ratio = 2.0, 2.5, and 3.0, the relationship exhibited a symmetrical, ratcheting, and butterfly-like trend with an increase in the number of cycles, and the minor axis variation increased with a larger major/minor axis length ratio. Furthermore, when the major/minor axis length ratio was fixed, the larger direction, the slower and smaller the minor axis variation.
As for the controlled curvature-number of cycles needed to buckling relationship, it was found that with larger major/minor axis length ratios, the number of cycles needed to initiate buckling decreased, and with larger directions, the number of cycles needed to initiate buckling increased. In addition, the controlled curvature-number of cycles needed to initiate buckling relationship on double logarithmic coordinates, under the same major/minor axis length ratio, four different directions appeared as four nearly parallel lines. Finally, this study summarized theoretical equations to describe the controlled curvature and the number of cycles needed to initiate buckling relationship of SUS 304 stainless steel elliptical tubes with different directions and different major/minor axis length ratios under cyclic bending The theoretical analysis was compared with experimental results, and it was found that the data from both approaches were very close, indicating that the theory could reasonably describe the experimental results.

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