本工作研究间歇超载(模拟一个大浪随后若干个小浪)对海洋结构的裂纹(如焊趾裂纹或母材内部的本质缺陷等)扩展速率的作用。实验结果表明,在3.5％NaCl溶液中,超载对裂纹扩展的延迟作用虽然比在空气中稍弱,但仍然很显著(比未超载的裂纹扩展率降低4～5倍);在小△K时,超载后的长裂纹扩展常出现短裂纹初期的扩展特征。 断口的扫描电镜砚察表明,在每次超载的高应变区有韧性撕裂痕迹,而靠近这些撕裂带常可看到二次裂纹。
It is believed that an overload may have significant influence on fatigue crack growth in air, but what influence it would have on corrosion fatigue crack growth in sea water was seldom reported. In this paper, the intermittent overload which simulated a sltuation that a number of small wave loads follow a big wave overload was investigated to see what would happen to the cracks in critical position, such as undercuts in weld toe or inherent defects in base metal for offshore structures. The results showed that in 3.5％ NaCl solution the overload effect on fatigue crack growth was still active, but the retardation effect of a single overload in tension was less than that in air. The reason for this may be very complex, which related to the dissolution reaction, solution pumping action as well as the effect of corrosion products. It was also found that there was little difference between the crack growth rates in 3.5％ NaCl solution when the overload ratio changed from 1.5 to 2. Fractographic observations of some specimens from SEM showed that high plastic strain appeared in the overload band and secondary cracks were found near those high strain areas.
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