拉伸载荷下穿透双裂纹干涉行为与合并准则研究

多裂纹的扩展与合并行为显著影响工程构件的剩余强度与使用寿命。为获得裂纹合并规律，对含不同长度和不同相对位置的非等长穿透双裂纹平板试样进行了拉伸试验，并基于延性损伤模型开展了有限元分析。结果表明，数值模拟中裂纹张口位移变化、扩展与合并行为与试验结果一致。此外，非等长穿透双裂纹长度及相对位置的变化，显著影响裂纹尖端的应力三轴度分布，进而影响双裂纹的合并行为。通过大量数值模拟分析，提出一种基于裂纹长度和相对位置的新合并准则。对照71组试验结果发现，新合并准则预测准确率高达84.5%；对照274组数值模拟结果发现，准确率高达91.2%。所提出的拉伸载荷下裂纹合并准则不仅具有显著高于现行含缺陷结构安全评定标准中合并准则的准确率，并且具有必要的保守性，可为工程构件中多裂纹合并与否提供有效判断。

Interaction Behavior and Combination Rules of Two Through-wall Cracks under Tensile Loading

The propagation and coalescence of multiple cracks significantly affect the remanent strength and service life of components. Tensile tests on plate specimens with two unequal through-wall cracks with different lengths and relative positions,together with corresponding finite element analysis based on a ductile damage model, are carried out to obtain the patten of crack coalescence. The results show that the crack opening displacement, propagation and coalescence behavior in numerical simulations are consistent with those in the experimental results. In addition, it is found that the variation of the length and relative positions of the two unequal through-wall cracks markedly affects the stress triaxiality distribution at the crack tip, which further affects the coalescence behavior of two cracks. Through a large number of numerical simulations, a new combination rule based on crack length and relative position is proposed. Based on the comparison with the results of 71 groups of tests and 274 groups of simulation results,it is found that the values of prediction accuracy of the new combination rule for the two types of tests are up to 84.5% and 91.2%,respectively. The proposed crack combination rule under tensile loading not only has a significantly higher accuracy than the combination rules in the current safety assessment standards for structures containing defects, but also has a necessary conservativeness, which can provide an effective judgment on whether the multiple cracks in components merge or not.