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利用测定疲劳裂纹增长速率的方法研究了在天然海水中阴极保护对低碳钢腐蚀疲劳裂纹增长性状的影响。假设临界应力强度因子幅值△K_(th)相当于(1～2)×10~(■)毫米/周的裂纹增长速率时的应力强度因子幅值,则在空气中△K_(th)为3.9兆牛顿/米~3/~2,在海水中为2.3牛顿/米~3/~2,而在海水中阴极极化(-800毫伏、相对 S.C.E)条件下为5.4兆牛顿/米~3/~2。应力强度因子幅值和裂纹增长速率之间关系在空气中增长速率为3×10~(-7)～2×10~(?)毫米/周和在海水中-800毫伏(相对 S.C.E)以及在海水中增长速率为1×10~(-7)～1×10_■毫米/周的情况下遵守 Paris 规律。发现在海水中的裂纹增长速率的最高值比在空气中的快两倍,但在海水中-800毫伏(S.C.E)条件下,其裂纹增长速率降低到约为在空气中裂纹增长速率范围内的40%。利用扫描电镜研究了试样腐蚀疲劳裂纹表面的断口组织。发现在海水中阴极极化的试样裂纹表面上形成钙质沉积物。在海水中阴极保护的试样出现腐蚀疲劳裂纹增长的终止现象可以解释为:由裂纹中海水生成的阴极反应钙质产物的楔入作用。
The effect of cathodic protection in natural seawater on corrosion fatigue crack growth of mild steel was investigated by measuring the rate of fatigue crack growth. Assuming that the magnitude of the critical stress intensity factor △ K th is equivalent to the magnitude of the stress intensity factor at the crack growth rate of (1 ~ 2) × 10 ~ (■) mm / week, △ K th 3.9 MPa / m ~ 3 / ~ 2, 2.3 N / m ~ 3 / ~ 2 in seawater, and 5.4 Million N / m in seawater with cathodic polarization (-800 mV vs. SCE) 3 / ~ 2. The relationship between the magnitude of stress intensity and the rate of crack growth is 3 × 10 -7 to 2 × 10 -3 mm / week in air and -800 mV (relative to SCE) in seawater and The Paris law is obeyed when the growth rate in seawater is 1 × 10 -7 ~ 1 × 10 -3 mm / week. The maximum rate of crack growth in seawater was found to be two times faster than in air, but its crack growth rate was reduced to about the range of crack growth rate in air at -800 millivolts (SCE) in seawater Of the 40%. The fracture structure of the surface of fatigue crack was studied by SEM. Calcium deposits were found on the cracked surface of cathodically polarized samples in seawater. The termination of corrosion fatigue crack growth in cathodic-protected samples in seawater can be explained by the wedging effect of the cathodic reaction of calcium products generated by the seawater in the crack.