本文旨在研究SUS304不鏽鋼直角扇形管於各式彎曲方向下的力學表現，核心在於解析對稱控制曲率循環彎曲負載對其力學響應與失效機制之影響。實驗設計中，選用外半徑為 20、30、40 與 50 mm 之直角扇形管，設定曲率控制範圍自 ±0.5、±0.55、±0.6、±0.65、±0.7、±0.75 m⁻¹，並針對 0°、15°、30°及45° 四種彎曲角度進行測試，所有試件壁厚均維持 1 mm。
研究發現，由彎矩–曲率關係曲線可看出，所有試件在循環負載下最終皆會趨於穩定的彈塑性迴圈。當彎曲方向固定，最大彎矩值會隨著扇形管外半徑的增加而提升；而在外半徑固定的情況下，彎曲角度越大，所測得的彎矩值也越高。透過觀察外半徑變形與曲率之關係，發現在循環次數增加時，不論尺寸或角度，其變形量均呈現對稱式的棘齒狀成長，且外半徑越大或角度越陡，其變形幅度越趨顯著。
在循環至失效方面，實驗指出在相同的控制曲率下，外半徑愈大的直角扇形管，其發生斷裂所需的循環次數愈短。若將曲率與失效圈數繪製於雙對數坐標，各外半徑試件均呈現明確的線性關係。最終，本研究建構了一套理論模型，用以定義不同規格SUS304不鏽鋼直角扇形管在各類彎曲條件下，其控制曲率與循環至損壞圈數間的連動規律。經比對，理論預測值與實測數據展現出高度一致性，證實該模型能精準描述SUS304不鏽鋼直角扇形管的彎曲失效特性。

This study aims to investigate the mechanical performance of SUS304 stainless steel right-angled sector-shaped tubes under various bending directions, with a core focus on analyzing the effects of symmetric curvature-controlled cyclic bending loads on their mechanical responses and failure mechanisms. In the experimental design, right-angled sector-shaped tubes with outer radii of 20, 30, 40, and 50 mm were selected. The curvature control ranges were set from ±0.5, ±0.55, ±0.6, ±0.65, ±0.7, and ±0.75〖" m" 〗^(-1), and testing was conducted across four bending angles: 0°, 15°, 30°, and 45°. The wall thickness of all specimens was maintained at 1 mm.
The research findings indicate, as observed from the moment–curvature relationship curves, that all specimens eventually tend toward a stable elastoplastic loop under cyclic loading. When the bending direction is fixed, the maximum bending moment increases with the outer radius of the sector-shaped tube. Conversely, under a fixed outer radius, a larger bending angle results in a higher measured bending moment. By observing the relationship between outer radius deformation and curvature, it was found that as the number of cycles increases, the deformation exhibits a symmetric, ratcheting-like growth regardless of size or angle. Furthermore, a larger outer radius or a steeper angle leads to a more pronounced deformation amplitude.
Regarding low-cycle fatigue life, the experiments indicate that under the same controlled curvature, right-angled sector-shaped tubes with larger outer radii require fewer cycles to reach failure. When the curvature and the number of cycles to failure are plotted on a log-log scale, a clear linear relationship is observed for specimens of each outer radius. Finally, this study constructs a theoretical model to define the relationship between the controlled curvature and the number of cycles to failure for various specifications of SUS304 stainless steel right-angled sector-shaped tubes under diverse bending conditions. Upon comparison, the theoretical predictions exhibit high consistency with the experimental data, confirming that the model can accurately describe the bending failure characteristics of SUS304 stainless steel right-angled sector-shaped tubes.

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