本研究主旨在探討應力比及頻率效應對AISI 347不銹鋼腐蝕疲勞性質之影響，分析在空氣、純水、NaCl及H2SO4水溶液中之高週疲勞及疲勞裂縫成長的差異性。在疲勞裂縫成長實驗方面，同時量測裂縫閉合程度，以了解裂縫閉合效應對疲勞裂縫成長速率之影響。此外，亦利用光學式顯微鏡(OM)及掃描式電子顯微鏡(SEM)觀察疲勞破斷面，以了解裂縫的生成及成長模式。 實驗結果顯示，不論應力比為R = 0.1或R = 0.5的狀態下，皆以H2SO4水溶液之高週壽命下降最多，其次為3.5 % NaCl水溶液。在長裂縫成長行為(stage II)方面，三種水溶液中之裂縫成長速率差異不大，而空氣中僅在R = 0.5時略低於其他環境，由此顯示高週腐蝕疲勞壽命主要消耗在裂縫起始階段。此外，平均應力的提升明顯導致AISI 347不銹鋼在各環境下之高週壽命降低及裂縫成長速率提高。在頻率效應方面，負荷頻率從5 Hz降至1 Hz，對AISI 347不銹鋼之腐蝕疲勞行為並無明顯的影響，僅在3.5 % NaCl中，腐蝕產物造成的裂縫閉合效應會因為頻率降低而明顯提高。 利用以負荷範圍及最大負荷值為參數所衍生之平均應力整合模式，可以有效的將不同應力比條件下的高週疲勞壽命及疲勞裂縫成長性質加以整合。而利用有效應力因子強度範圍DKeff來評估不同應力比對AISI 347不銹鋼的裂縫成長行為的影響，則有最佳的效果。 The aim of this study is to investigate the influence of load ratio and frequency on the corrosion fatigue behavior of AISI 347 stainless steel in different environments. In particular, the high-cycle fatigue (HCF) and fatigue crack growth (FCG) behavior in air, water, NaCl, and H2SO4 solutions under several load ratios and frequencies were made a comparison. Crack opening levels were also measured in order to characterize the crack closure effects on FCG behavior. Fractography and microstructural analyses with optical microscopy (OM) and scanning electron microscopy (SEM) were conducted to investigate the corrosion fatigue crack initiation and propagation mechanisms. Results showed that, for a given cyclic loading condition, the fatigue strength of AISI 347 stainless steel was the lowest in H2SO4 solution followed by NaCl solution. However, the FCG rates in the given three aqueous environments were almost equivalent and not significantly different from those in air. These results implied that the initial fatigue cracking stage controlled the HCF life of AISI 347 stainless steel. An increase in mean stress level resulted in a faster crack growth rate and a shorter fatigue life for AISI 347. Decreasing loading frequency from 5 Hz to 1 Hz had no significant effect on the corrosion fatigue behavior of AISI 347 stainless steel except in 3.5 % NaCl where greater crack closure effect due to corrosion products was found in the lower frequency. A concept of using the range and peak value of the applied loading as the driving force parameters was applied to evaluate the load ratio effects on the HCF and FCG behavior without invoking the crack closure data. However, the effective stress intensity factor range, DKeff, provided a better means to describe the FCG behavior at various load ratios in the given environments.
