本研究旨在探討不同幾何尺寸之SUS304不鏽鋼直角扇形管，在各類循環彎曲負載作用下的力學行為與失效機制。實驗設計涵蓋四種不同直角外半徑尺寸分別為:20、30、40及50 mm，所有管壁厚皆為1 mm為之直角扇形管，並施加六種預設的對稱控制曲率分別有:±0.5、±0.55、±0.6、±0.65、±0.7和±0.75 m-1進行循環彎曲至損壞的測試。透過實驗獲取之數據，本研究詳細解析了在循環負載下的彎矩-曲率、外半徑變化與曲率之關聯，並進一步探討控制曲率與循環至損壞圈數之間的關係。
實驗結果顯示，彎矩-曲率關係呈現典型的滯後迴圈特性。隨著直角扇形管外半徑增大，結構表現出更顯著的循環軟化現象；此外，外半徑變化隨曲率增加呈現對稱性變化，且較大外半徑之管件，其形變發展趨勢更為劇烈。在失效方面，數據顯示在相同控制曲率下，外半徑越大，其抗失效能力越弱，循環至損壞的圈數顯著下降。若將此關係繪製於雙對數坐標系中，可發現不同外半徑對應出一系列線性趨勢。最後，本研究建立對應的理論分析模型，經驗證後，理論預測值與實驗數據吻合度高，證實了本研究所提模型的準確性與一致性。

This study aims to investigate the mechanical behavior and failure mechanisms of SUS304 stainless steel right-angle fan-shaped tubes with various geometric dimensions under cyclic bending loads. The experimental design encompasses four outer radius sizes (Ro = 20, 30, 40, and 50 mm), all featuring a constant wall thickness of 1 mm, subjected to six symmetric curvature control conditions (κ = ±0.5, ±0.55, ±0.6, ±0.65, ±0.7, and ±0.75 m-1) until failure occurs. Based on the acquired experimental data, the correlations among moment-curvature, outer radius variation-curvature, and the relationship between controlled curvature and damage life (Nf) under cyclic loading are comprehensively analyzed.
The experimental results indicate that the moment-curvature relationship exhibits typical hysteresis loop characteristics. With an increase in the outer radius of the right-angle fan-shaped tubes, a more pronounced cyclic softening phenomenon is observed in the structure. Furthermore, the variation in the outer radius displays a symmetric trend with increasing curvature, where tubes with larger outer radii exhibit a more severe deformation tendency. Regarding structural failure, the data demonstrate that under identical controlled curvatures, a larger outer radius leads to lower failure resistance, resulting in a significant reduction in the number of cycles to failure. When plotted in a double-logarithmic coordinate system, the curvature-damage life relationships for different outer radius exhibit a series of distinct linear trends. Finally, a corresponding theoretical analysis model is established. The validation results show high agreement between the theoretical predictions and the experimental data, confirming the accuracy and consistency of the proposed model.

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