圓管在實際工業結構物應用中常承受循環彎曲的負載，循環彎曲負載會造成圓管橫斷面產生橢圓化的變化，且隨著負載循環次數的增加，橢圓化亦會隨著增加，最後當到達某個循環次數時，該圓管會產生皺曲的損壞現象。不同的外徑/壁厚比的圓管承受不同曲度率循環彎曲負載時，由於外徑和壁厚的變化不同以及圓管承受不同的曲度加載率負載時，必定會產生不同的力學行為反應；此外不同外徑和壁厚的變化與不同的曲度加載率負載也會造成圓管管面橢圓化的變化有很大的不同，這些變化將進一步影響皺曲的發生時機。所以不同外徑/壁厚比圓管受不同曲度加載率的循環彎曲負載，其力學行為以及皺曲損壞的研究對工業結構物是相當重要的課題。針對此課題本文提出下列的研究。
實驗方面：本實驗採用“彎管試驗機”及“曲度－橢圓化量測器”來控制對稱曲度下，不同外徑/壁厚比的SUS 304不銹鋼圓管承受不同曲度加載率的循環彎曲負載實驗。實驗結果顯示，圓管的外徑越小，管徑面越易橢圓化，且產生皺曲所需循環圈數越少。此外，SUS 304不銹鋼圓管在循環彎曲負載下，彎曲曲度率越快，不銹鋼管有較硬化的現象發生，而管徑面的橢圓化也因較快彎曲曲度率而增加，使到達皺曲時的循環次數較少。
理論方面：針對不同的外徑/壁厚比的圓管承受不同曲度加載率的循環彎曲負載皺曲損壞的理論，本文是將Kyriakides 和Shaw (1987)、Pan 與 Her (1998)及Lee、Pan 與 Kuo (2001)所提出的理論加以整合及修改，修改後的理論可用來描述不同外徑/壁厚比的圓管承受不同曲度加載率的循環彎曲負載時，循環至皺曲的次數、彎曲曲度率、不同外徑/壁厚比和控制曲度量的關係。實驗和理論結果比較顯示，理論能合理的描述實驗的結果。

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