本文用单轴拉伸中心斜裂纹平板试样对18-8不锈钢/42％MgCl_2(沸)进行了一系列复合型应力腐蚀试验。结果表明,复合型加载条件下,应力腐蚀开裂方向与裂端最大正应力面方向一致;但是应力腐蚀裂纹起始扩展的临界抗力却随K_Ⅱ/K_Ⅰ值增大而降低。根据阳极溶解型应力腐蚀的“滑移 溶解”机制,本文从复合型加载比对裂端应力状态及塑性变形程度的影响就上述结果进行了讨论,并指出:在断裂分析中简单地使用Ⅰ型测试结果,并把复合型裂纹当作Ⅰ型裂纹处理是不安全的。
A series of mixed mode tests were carried out on 18-8 stainless steel in boiling 42％ MgCl_2 solution. The results show that for any K_(II)/K_I ratio, the SCC direction coincides well with the crack tip maximum normal stress plane, while the SCC resistance of the material reduces as the ratio of K_(II)/K_I increases. The experimental results were discussed in the light of anode dissolving mechanism and the effect of mixed mode loading on crack tip stress and strain. It is concluded that for fracture analysis if mixed mode cracks were simply taken into account as mode I cracks, and only mode Ⅰ testing results as well as mode Ⅰ fracture criterion were employed, it may not be safe.
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