本研究旨在探討 SUS304 不鏽鋼直角扇形管在 -1、-0.5 與 0 三種曲率比下，其承受循環彎曲負載時的外半徑變化量與損壞行為。直角扇形管試件外半徑包括 20、30、40 與 50 mm，藉此觀測幾何尺寸對管件劣化行為的具體影響。透過分析彎矩、外半徑變化量與曲率之響應關係，本研究揭示了直角扇形截面在不同循環下的力學行為特徵，為相關工程結構的設計優化提供依據。
實驗結果顯示，直角扇形管在承受循環彎曲負載下，其外半徑變化量會隨著往復加載圈數的增加而呈現持續遞增之趨勢。在幾何規格的尺寸效應方面，試件的橫截面畸變行為深受外半徑尺寸影響；當外半徑由 20 mm 增大至 50 mm 時，其對應的最大變化量隨之增加，顯示較大外半徑之規格在彎曲進程中具有較高的畸變敏感度。進一步剖析變形軌跡的動態特徵，在各圈加載進程中，當彎曲曲率接近最大加載端時，外半徑變化量的上升速率會隨之加快，致使響應曲線之斜率增大；而在卸載回歸至零曲率基準時，試件則因塑性不均勻形變而留下殘餘形變。此殘餘形變隨著循環週期的推進而逐圈累積，導致整體的迴圈呈現向上漂移的棘齒行為，且該殘餘變形的累積幅度與上移趨勢亦隨外半徑尺寸的增大而更為明顯。
在損壞分析方面，循環至損壞圈數隨曲率範圍增加而遞減。實驗證實，較大外半徑與趨近於 0 的曲率比會加速幾何劣化並縮短損壞圈數。若將曲率範圍與循環至損壞圈數關係繪製於雙對數座標系時，數據呈現優異線性相關，說明其損壞行為具有高度規律性。最終，本研究建立的理論預測模型與實驗結果高度一致，證實該模型對不同尺寸之直角扇形管具備良好的可靠度評估能力。研究成果填補了扇形管在循環塑性力學領域的研究空白，可作為後續機械結構設計與壽命預測的專業參考。

This study investigates the cross-sectional distortion and fatigue failure of SUS304 stainless steel right-angle sector tubes subjected to cyclic bending. Specimens with outer radii of 20, 30, 40, and 50 mm were evaluated under three curvature ratios including -1, -0.5, and 0. Experimental results indicate that outer radius deformation continuously increases with cycle count, with a larger outer radius exhibiting higher distortion sensitivity. Non-uniform plastic deformation induces progressive residual strain accumulation, generating an upward-drifting sawtooth trajectory that becomes more pronounced at larger dimensions. Failure analysis reveals that the number of cycles to failure decreases with increasing curvature range, where a larger outer radius and a curvature ratio approaching zero accelerate geometric degradation. Plotted on double-logarithmic coordinates, the relationship between curvature range and cycles to failure displays excellent linear correlation. Ultimately, the established theoretical model effectively captures the experimental trends across various geometries, providing a reliable framework for life assessment and structural design of sector tubes.

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