不同尖銳凹槽深度304不銹鋼管在循環彎曲負載下黏塑性行為之實驗分析

Experimental Analysis on the Viscoplastic Behavior of Sharp-Notched 304 Stainless Steel Tubes with Different Notch Depths Under Cyclic Bending

本文主要係實驗分析五種不同尖銳凹槽深度 （0.2、0.4、0.6、0.8 及1.0 mm）的304 不銹鋼管在三種不同加載曲度率 （0.0035、0.035 及0.35 m-1s-1） 循環彎曲負載下的力學行為與皺曲損壞 （黏塑性行為）。實驗係透過彎管試驗機與曲度－－橢圓化量測器來進行實驗數據的控制、量測及蒐集。實驗結果顯示，不論任何凹槽深度，304 不銹鋼管的彎矩－－曲度關係會呈現循環硬化的現象，且最後彎矩－－曲度曲線會形成一穩定的迴圈。而橢圓化－－曲度關係則呈現不對稱棘齒狀的變化，且凹槽深度越深，曲線的不對稱現象會越明顯。由雙對數座標中曲度－－循環彎曲至皺曲圈數的實驗關係中發現，在個別的加載曲度率循環彎曲負載下，五個不同尖銳凹槽深度的試件可近似為五條幾乎平行的直線。最後，本文參考Shaw 和Kyriakides及 Pan 和Her論文中的理論方程式後，提出一個可以描述不同尖銳凹槽深度的304 不銹鋼管在不同加載曲度率循環彎曲負載時，控制曲度與循環彎曲至皺曲圈數關係的理論方程式。在與實驗值做比較後發現，理論分析能合理的描述實驗結果。

This paper presents an experimental investigation of the mechanicalbehavior and buckling failure (viscoplastic behavior) of 304 stainless steeltubes with five different sharp-notched depths (0.2, 0.4, 0.6, 0.8 and 1.0mm) subjected to cyclic bending with three different curvature-rates(0.0035, 0.035 and 0.35 m-1s-1). A tube bending machine and curvature-ovalization measurement apparatus were used to control, measure andcollect experimental data. It can be observed from the experiment datathat the 304 stainless steel tube with any notch depth exhibits a cyclichardening phenomenon from the moment and curvature relationship, anda steady-state loop of the moment-curvature curve is found after a fewloading cycles. It can also be observed that the relationship between theovalization and curvature demonstrates a nonsymmetric, ratchetingphenomenon. Higher notch depth leads to further nonsymmetry of thecurve. It can be observed from the experimental curvature-number ofcycles to produce buckling curves that five almost parallel straight linescan be found for five different sharp-notched depths at each curvature-ratein a log-log scale. Finally, by referring to the theoretical formulationsproposed by Shaw and Kyriakides [1], and Pan and Her [2], a theoreticalformulation was proposed to simulate the relationship between the controlledcurvature and the number of cycles to produce buckling for 304stainless steel tubes with different sharp-notched depths at differentcurvature-rates. By comparing theoretical analysis with experimental data,it is shown that the theoretical formulation can properly represent theexperimental results.