力学失配对电子束焊接接头疲劳裂纹扩展行为的影响

Influence of Mechanical Mis-match on Fatigue Crack Growth Behavior of Electron Beam Welded Joints

研究了高温合金电子束焊接接头区的疲劳裂纹扩展行为 ,深入分析了接头区力学失配对疲劳裂纹扩展方向及疲劳裂纹扩展速率的影响规律。结果表明 ,由于力学不均匀性的影响 ,电子束焊接接头的疲劳裂纹扩展具有不稳定性 ,位于高匹配焊接区的疲劳裂纹偏离原裂纹扩展方向 ,跨越焊接区与母材 ,呈复合型扩展 ;焊接区疲劳裂纹的偏转使得裂纹尖端有效应力强度因子减小 ,从而焊缝区裂尖局部有效裂纹扩展驱动力下降 ,导致接头的疲劳裂纹扩展速率下降 ,故此高匹配接头对疲劳裂纹扩展有一定的屏蔽作用 ;疲劳裂纹扩展强烈地受裂纹尖端塑性区尺寸和形状影响 ,含疲劳裂纹的焊接结构完整性主要取决于低流变应力区材料的韧性。

The influences of mechanical mis-match on crack growth direction and crack growth rate were studied based on the analysis of fatigue crack growth behaviors in electron beam welded joints of supperalloy,The results showed that the fatigue crack growth of electron beam welded joints was instable due to the influence of mechanical heterogeneity.The fatigue crack located in welded seam of overmatched joints deviated from its original growth direction,then spanned weld zone and base metal at a mixed mode while propagating.The effective growth driving force at the tip of fatigue crack reduced with the reducing of effective stress intensity factor owing to crack deviation of weld zone,which led to the fatigue crack rate deduced.For this reason,the overmatched joints have the capacity of protecting fatigue crack joints from fast growth.Fatigue crack was strongly affected by size and symmetrical characteristic of plastic zone at crack tip,so the integrity of welded structure containing fatigue crack mainly depended on the toughness of lower strength zone.