凹槽效應對AISI 347不銹鋼高週腐蝕疲勞性質之影響 ;Notch Effect on High-Cycle Corrosion Fatigue for AISI 347 Stainless Steel

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题名:	凹槽效應對AISI 347不銹鋼高週腐蝕疲勞性質之影響;Notch Effect on High-Cycle Corrosion Fatigue for AISI 347 Stainless Steel
作者:	郭柏甫;Po-Fu Kuo
贡献者:	機械工程研究所
关键词:	局部酸化;多裂縫起始;腐蝕疲勞;凹槽效應;notch effect;localized acidification;corrosion fatigue;multiple crack initiation sites
日期:	2003-06-27
上传时间:	2009-09-21 11:41:25 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	本研究主旨在探討凹槽效應對AISI 347不銹鋼高週腐蝕疲勞性質之影響，分析在不同環境中(空氣、純水、3.5% NaCl、3.5% NaCl + Inhibitor及H2SO4水溶液)的高週疲勞壽命差異。另探討不同應力比(R = -1, R = 0.1與R = 0.5)下，平滑試棒之高週腐蝕疲勞性質。此外，亦利用掃描式電子顯微鏡(SEM)觀察疲勞破斷面，以了解疲勞破壞機制。實驗結果顯示，AISI 347不銹鋼之不同形狀試棒，在空氣及四種水溶液中之高週疲勞壽命皆有隨應力集中因子的增加而減少之趨勢，而腐蝕環境中之缺口敏感度以純水及鹽水加抑制劑較高。分別比較平滑試棒與半圓形凹槽試棒之各環境間應力-壽命曲線，各曲線有清楚差異，由高至低依序為空氣、鹽水加抑制劑、純水、鹽水與H2SO4水溶液。V形凹槽試棒之應力-壽命曲線圖則分為兩群，空氣與鹽水加抑制劑為一群，而另一群為純水、鹽水及H2SO4水溶液，此現象主要是因V形凹槽試棒的局部酸化程度比半圓形凹槽試棒嚴重所造成。平滑試棒在純水、鹽水及H2SO4水溶液中與空氣作比較，在應力比R = 0.1與R = 0.5之條件下，皆以H2SO4水溶液之高週疲勞壽命下降最多，其次為3.5 % NaCl水溶液，然而在R = -1時，各環境之高週疲勞壽命差異不大，此乃因為表面滑移帶在R = 0.1及R = 0.5有平均拉應力的情況下較容易生成，與腐蝕環境作用後，會更加降低其疲勞強度。本研究利用最大應力、應力範圍和最大應力體積或最大應力表面積為整合參數，求得一涵蓋凹槽效應之通用疲勞評估模式，對不同環境下之不同形狀試棒的高週疲勞壽命有不錯的描述性。在破斷面的觀察方面，因應力集中效應的作用，導致V形凹槽試棒之破斷面與平滑及半圓形凹槽試棒不同。V形凹槽試棒，不論在高應力或低應力區均為多裂縫起始點，平滑試棒的疲勞裂縫皆由單一點起始，而半圓形凹槽試棒在低應力區時，同樣為單一點起始，但在高應力區時，則呈現多裂縫起始點。 The aim of this study is to investigate the influence of notch effect on the high-cycle corrosion fatigue properties of AISI 347 stainless steel in various environments, namely, air, water, NaCl, NaCl plus inhibitor, and H2SO4 solutions. The effect of load ratio on the high-cycle corrosion fatigue behavior was also studied for smooth specimens. Fractography analysis with scanning electron microscopy (SEM) was conducted to investigate the fatigue fracture modes. Results showed that the fatigue lives in various specimen geometries tested in air and four aqueous environments were decreased with increasing stress concentration factor, and the fatigue notch sensitivity among the corrosion environments was higher in water and 3.5% NaCl solution added with inhibitor. For smooth and semi-circular notch specimens, the rank of fatigue strength in the given environments took the following order: air > salt water plus inhibitor > water > salt water > sulfuric acid solution. For V-notch specimens, the S-N curves were separated into two groups; i.e., one group with air and 3.5% NaCl plus inhibitor and the other with water, 3.5% NaCl and H2SO4. This was attributed to a greater effect of localized acidification occurring at the root of V-notch as compared to smooth shape and semi-circular notch. For R = 0.1 and 0.5, the fatigue strength of smooth specimen showed the lowest value in H2SO4 solution while at R = -1 with zero mean stress, the fatigue strength was no significant difference among the given environments. A parameter incorporating with the maximum stress, stress amplitude and highly stressed volume (or area) was introduced and well correlated with the fatigue life of various specimen geometries in the given environments. Fractography analysis results indicated the multiple crack initiation sites were found in V-notch specimens whiles single crack initiation site was observed for smooth and semi-circular notch specimens at low applied stress levels.
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