中文摘要：

为评估现有结构完整性评定规范中裂纹合并准则的保守性,采用有限元分析技术预测循环载荷下含一对等大半椭圆表面裂纹的有限厚度平板的疲劳寿命。采用两种不同材料（304不锈钢和16Mn R钢）参数,对不同初始深度比、形貌比、最小间距的22组裂纹平板的剩余寿命进行了预测,并讨论了现有的三类合并准则和一种由本文提出的合并准则的保守性。与利用考虑干涉直接计算得到的剩余寿命相比较,其结果表明,现有合并准则的保守性与裂纹相对板厚的尺寸密切相关。在初始裂纹深度较大的情况下,BS 7910和ASME建议的合并准则可能会得到不保守的结果,而A16,API 579-1和GB/T 19624—2004建议的合并准则过于保守。建议当两裂纹的最小间距与平均裂纹深度相等,即s=（a1＋a2）/2时,可将两个表面裂纹表征为一个大裂纹。最后,通过对裂纹扩展速率公式中材料参数的敏感性分析,发现合并准则的保守度还与所用材料的裂纹扩展速率有关,其中Paris公式中的指数n起关键作用,而系数C的影响甚微。

英文摘要：

The remnant fatigue lives of finite thickness plates containing a twin of semi-elliptical surface cracks under cyclic loadings are predicted by using finite element simulation technique in order to assess the conservatism of coalescence criteria in the existing structural integrity assessment standards. Twentytwo groups of crack configurations and two different material properties（ 304 stainless steel and 16 Mn R steel） are used in the analysis. The conservative degrees of three existing crack coalescence criteria and one type of combination rule presented by authors are discussed. Compared with the remnant lives obtained by the method considering interaction,the results show that the conservative degrees of the existing combination rules are highly dependent on the relative size of crack to wall thickness. Combination rules suggested by BS 7910 and ASME may lead to non-conservative results when initial crack depth is large.In addition,the rules suggested by A16,API 579- 1 and GB / T 19624—2004 are over conservative. The paper proposes a new combination rule i. e. the minimum distance between cracks being equal to the average crack depth. By conducting sensitivity analysis of parameters in the formula for correlating crack growth rates,it is also found that the conservative degree of the combination rule is significantly dependent on the exponent n in Paris law but is marginally affected by the coefficient C.