Quantitative Evaluation of Environmental Effects on Irreversibility of Cyclic Plastic Deformation by STM Observation

为了更好地了解环境对疲劳的影响，本文对各种气体环境中的疲劳裂纹扩展进行了研究。在控制湿度、氮气、氩气和真空的实验室空气中，对钛、8090铝锂合金和Fe-3%Si合金进行了恒载荷幅疲劳裂纹扩展试验。与真空条件相比，在任何气体环境中获得了增加的疲劳裂纹扩展速率。在实验室控制的空气条件下，对8090铝锂合金进行了恒定DELTAK疲劳裂纹扩展试验，以评估水蒸气对疲劳裂纹扩展的影响。实验室空气的相对湿度（RH）在0.01%至40%的范围内系统地变化。随着相对湿度的增加，疲劳裂纹扩展速率增加。在0.01%~ 30%RH范围内，裂纹扩展速率增加，超过30%RH后，裂纹扩展速率基本不变。在真空条件下没有观察到裂纹分层。用扫描隧道显微镜对Fe-3%Si合金的疲劳表面形貌进行了精确的观察和定量评价。进一步的实验研究，使用原子力显微镜是非常必要的，以评估环境对疲劳裂纹萌生和扩展的影响。

To get a better understanding of the enviromental influence on fatigue, a study has been undertaken on the fatigue crack growth in various kinds of gaseous environments. Constant load amplitude fatigue crack growth tests were performed in titanium, 8090Al-Li alloys and Fe-3%Si alloys under laboratory air with controlled humidity, nitrogen, argon and vacuum. Increased fatigue crack growth rates were obtained in any gaseous environments compared to that for the vacuum condition. Constant DELTAK fatigue crack growth tests were also performed for the 8090 Al-Li alloys under the controlled laboratory air condition to evaluate the effect of water vapor on the fatigue crack growth. The relative humidity (RH) of the laboratory air were systematically changed in the range of 0.01% to 40%. Fatigue crack growth rates were increased as increase in the relative humidity. However, the increase was observed in the range of 0.01% to 30%RH,and over the 30%RH the crack growth rates were unchanged. No crack delamination was observed in the vacuum condition. Precise observation and quantitative evaluation of the fatigue surface morphology of Fe-3%Si alloys have been made using an STM (Scanning Tunneling Microscope). Further experimental research using AFM is strongly required in order to evaluate the environmental effects on the fatigue crack initiation and growth.