中文摘要：

异种金属焊接接头是核电系统内部易损部件，为保证其安全使用，需要对其进行准确的完整性分析。为了理解含缺陷异种金属焊接接头的断裂表现，确定现有程序对异种金属接头评定的适用性。本文对镍基合金52M异种金属接头不同位置裂纹的三点弯曲试样进行了断裂试验。发现试样的裂纹扩展阻力及路径不同，且裂纹路径总是向低屈服强度材料侧偏转。得出裂纹路径的偏转主要由裂尖材料强度失配控制，而非韧性失配控制。对于扩展路径有偏斜的裂纹，其乒R阻力曲线反映的是沿裂纹扩展区材料的表观断裂阻力，而非初始裂纹尖端区材料的本质断裂阻力。在不考虑焊接热影响区、界面区及内部影响区断裂阻力的情况下，采用现有程序去评定含缺陷异种金属接头，将产生非保守或过于保守的评定结果，且在多数情况下，得到非保守的评价结果。

英文摘要：

Background： Dissimilar metal welded joints （DMWJs） were indicated to be vulnerable components in the primary systems, an accurate structural integrity assessment for such DMWJ is needed. Purpose： Understand the fracture performance of the welded joint containing defects, determine if appropriate to assess the defects in the weld joint with the present codes. Methods： The fracture tests of the initial crack located in the different positions of Alloy 52M DMWJ specimens were carried out by using single-edge notched bend （SENB） method. Results： Different crack resistance and crack propagation path were obtained for the SENB specimens, and the cracks always deviate to the materials with lower strength. Conclusions： The crack path deviation is mainly controlled by strength mismatch, rather than toughness mismatch. The J-resistance curves with larger crack path deviation only reflect the apparent fracture resistance along the crack growth region, rather than the intrinsic fracture resistance of the initial crack-tip region material. Without considering the local fracture resistance properties of heat affected zone （HAZ）, interface region and internal affected region （IAZ）, following present assessment codes will unavoidably produce non-conservative or excessive conservative assessment results. In most cases, the assessment results will be potentially non-conservative.