本文主要為實驗探討不同內外直徑圓管（SUS304與316L不銹鋼管）在循環彎曲負載下的力學行為與挫曲損壞行為。本文係運用彎管試驗機與曲率-橢圓化量測器來進行不同的曲率控制循環彎曲負載至挫曲的實驗。實驗試件為三種不同大小的內外直徑與三種不同外徑/壁厚(Do/t)比的316L與SUS 304不銹鋼管。根據實驗結果顯示，彎矩-曲率曲線在曲率控制循環彎曲負載時，316L與SUS 304不銹鋼管皆有循環硬化的現象，而經過一些循環圈數後迴圈會呈現較為穩定的狀態。至於橢圓化-曲率的實驗曲線中顯示，橢圓化會漸增且呈對稱棘齒的變化，且橢圓化會隨著循環圈數一直增加直到薄壁管發生挫曲。此外，從對數座標中的控制曲率和循環彎曲至皺曲次數關係曲線發現，三種不同大小的內外直徑中的三種不同Do/t比的試件皆可獲得三條幾乎是平行的直線。最後，根據所測試的實驗結果，提出針對三種不同大小管徑與三種不同Do/t比的316L與SUS 304圓管，控制曲率和循環彎曲至皺曲次數關係的理論模式。在與實驗的數據比較後顯示，理論分析能合理的描述實驗結果。

This thesis presents an experimental investigation on the mechanical behavior and buckling failure of circular tubes (316L and SUS 304 stainless steel tubes) with different outside and inside diameters subjected to cyclic bending. In this study, the tube bending machine and curvature-ovalization measurement apparatus were used to conduct the curvature-controlled cyclic bending to buckling test. Three different outside and inside diameters with three different outside-diameter / wall-thickness (Do/t) ratios of 316L and SUS 304 stainless steel tubes were tested. It can be observed from the experimental moment-curvature curves that the SUS 304 and 316L stainless steel tubes harden cyclically and become steady after a few cycles for curvature- controlled cyclic bending. As for the ovalization-curvature curve, the ovalization of the tube cross-section increases in a ratcheting manner with the number of cycles. Owing to the progressive accumulation of the ovalization of the tube cross-section during cyclic bending, the tubes buckle eventually. In addition, three almost parallel straight lines were observed from the relationship between the controlled curvature and the number of cycles to produce buckling for three different outside and inside diameters with three different Do/t ratios of steel tubes in the log-log scale. Finally, a theoretical formulation was proposed to simulate the relationship between the controlled curvature and the number of cycles to produce buckling for three different outside and inside diameters with three different Do/t ratios of circular tubes. When compared with the experimental data, the theoretical analysis can properly simulate the experimental result.

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