基于Tanaka-Mura模型的电子束焊接头疲劳裂纹萌生模拟

为揭示高温合金电子束焊接头的疲劳特性，对其开展了疲劳裂纹萌生数值模拟研究。考虑焊缝区微观组织特性，对Voronoi图法进行改进，建立了焊缝区包含柱状晶、细等轴晶及粗等轴晶的混合晶区微观组织模型；对ABAQUS进行二次开发，考虑晶粒随机取向，生成晶粒多滑移带模型。基于Tanaka-Mura位错滑移模型，编写了疲劳裂纹萌生算法，考虑晶界处裂纹的连接与合并，对算法进行了改进，并结合有限元计算建立了电子束焊接头疲劳裂纹萌生数值模拟方法。基于上述方法对GH4169电子束焊接头不同载荷大小的疲劳裂纹萌生进行数值模拟，分析了裂纹萌生过程及萌生寿命，并与试验结果进行对比验证；还探讨了不同热影响区晶粒尺寸对焊接接头疲劳裂纹萌生的影响规律。结果表明，电子束焊接头疲劳裂纹均萌生于热影响区，但随着载荷水平的提高，萌生位置向熔合区一侧靠近；当热影响区晶粒尺寸与母材区晶粒尺寸越接近时，接头疲劳寿命越长。

Simulation of Fatigue Crack Initiation of Electron Beam Welding Joint Based on Tanaka-Mura Model

In order to reveal the fatigue performance of superalloy electron beam welded joints, the numerical simulation of fatigue crack initiation was carried out. Considering the microstructure characteristics of the weld zone, the Voronoi diagram was improved to establish the microstructure model of the multi grain including columnar grain, fine equiaxed grain and coarse equiaxed grain in the weld zone. ABAQUS soft was redeveloped and a grain multi-slip band model was generated by considering the random grain orientation. Based on the Tanaka-Mura dislocation model, a fatigue crack initiation algorithm was developed. Considering the connection and coalestion of cracks at grain boundaries, the algorithm was improved, and a numerical simulation method for fatigue crack initiation of electron beam welded joints was established based on finite element calculation. Based on the above methods, the fatigue crack initiation of GH4169 electron beam welded joint under different load sizes was numerically simulated. The crack initiation process and initiation life were analyzed and verified by comparison with the experimental results. The effects of grain sizes in different heat affected zones on fatigue crack initiation of welded joints are also discussed. The results show that the fatigue cracks of electronic welding joints are all initiated in the heat-affected zone (HAZ), but the initiation location is closer to the side of the fusion zone with the increase of load level. When the grain size of HAZ is closer to that of base metal, the fatigue life of joints will be longer.