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为了得到海水中钢的慢速腐蚀疲劳裂纹增长的实验数据,业已建立了一种对十二条裂纹同时进行研究的专用技术设备和试验程序。研究注重于对试验条件加以选择和控制,典型条件有BS436050D钢,t=12℃,应力比R=0.02—0.06。本文主要结果以裂纹扩展速度da/dN的形式给出,da/dN以10~(-7)～10~(-5)毫米/周次的低da/dN范围内的应力强度幅△K的函数的形式表示,对这些结果进行统计处理并评价了各种参数的意义。本文已经指出了与空气比较人工海水的显著影响,并说明了电化学电位和裂纹深度的重要影响,据本研究所得结果表明,对于浅裂纹,各种腐蚀条件可最大地增大裂纹增长率,同时,通过阴极保护又可最有效地减小裂纹增长率。本文指出,就这些影响来说,对初始裂纹深度a=1—3毫米和初始裂纹深度a=3—7毫米这两种裂纹是迥然不同的。在本研究中未明显地揭示在10和60周/分的两种加载频率下以及-800和-1100毫伏的不同电位下裂纹增长率的可能差异。虽然在所研究的范围内,这些差异似乎是小的,但特别低的电位和不同频率的通常影响是很重要的,因而应在将来的工作中予以校核。未来的工作,也应进一步研究较高R值和其它参数之影响。
In order to obtain experimental data on the slow corrosion fatigue crack growth of steel in seawater, a special technical equipment and test procedure for simultaneously studying twelve cracks have been established. The study focuses on the selection and control of test conditions, typical conditions are BS436050D steel, t = 12 ℃, stress ratio R = 0.02-0.06. The main results of this paper are given in the form of crack growth rate da / dN with da / dN in the range of 10 ~ (-7) ~ 10 ~ (-5) mm / The formal representation of the functions, the statistical processing of these results and the evaluation of the significance of the various parameters. This article has pointed out the significant impact of artificial seawater compared to air and illustrates the important effects of electrochemical potentials and crack depth. The results obtained from this study show that for shallow cracks, various corrosion conditions can maximize the rate of crack growth, At the same time, the crack growth rate can be reduced most effectively by cathodic protection. It is pointed out in the paper that for these effects, the two types of cracks are very different for the initial crack depth a = 1-3 mm and the initial crack depth a = 3-7 mm. The possible differences in crack growth rates at two loading frequencies of 10 and 60 cycles per minute and at different potentials of -800 and -1100 mV are not clearly revealed in this study. Although these differences appear to be small within the scope of the study, the very low potentials and the usual effects of different frequencies are important and should be checked in future work. Future work, should also further study the impact of higher R values and other parameters.