基于电磁加载的孔动态冷挤压强化方法

Dynamic Cold Expansion Method of Holed Structures Based on Electromagnetic Load

为了提高开孔结构的疲劳寿命,提出了一种基于电磁加载的动态冷挤压方法。试验对比了动态冷挤压和传统冷挤压的疲劳寿命增益,对挤压阻力和冷挤压前后孔的几何尺寸进行了测量,同时对动态冷挤压和传统冷挤压试件的疲劳寿命进行了评估,并对疲劳破坏机理及增寿机理进行了探讨。结果表明,与传统冷挤压相比,动态冷挤压能显著降低挤压阻力,且冷挤压后孔径沿轴向分布更加均匀。在疲劳试验中,动态冷挤压的试件比传统冷挤压的试件具有更高的疲劳寿命,特别是在高载荷水平下动态挤压疲劳寿命增益更明显。此外,通过疲劳断口观察发现动态冷挤压试件往往会出现多个疲劳源,且疲劳裂纹一般沿水平方向扩展,而传统冷挤压试件的疲劳裂纹一般萌生于芯棒入口处并向出口处扩展,说明动态冷挤压方法可能会沿轴向得到比静态方法更加均匀的残余应力,因此提高了开孔结构的疲劳寿命。

A novel dynamic cold expansion method based on electromagnetic load was developed to enhance the fatigue life of open hole structures.The experiments were conducted to investigate the method,and the corresponding static cold expansion method was also investigated as comparison.The expansion resistance was evaluated.The geometric dimension varieties of holes after cold expansion were measured.Moreover,the fatigue life of specimens after both methods were assessed,and the fatigue failure and fatigue life enhancement mechanisms were discussed.The results show that dynamic cold expansion can obviously reduce expansion resistance compared with static cold expansion and generate more uniform hole diameter distribution along the hole axial direction after cold expansion.In fatigue tests,specimens worked by dynamic cold expansion method exhibited the higher fatigue life than that worked by static cold expansion method,especially under high load level.Furthermore,through fatigue fracture observed dynamic cold expansion specimen will often appear many fatigue source,general along the horizontal direction and the fatigue crack propagation,and the tradition of cold expansion specimen fatigue crack initiation in the entrance of mandrel and extend to the exit,that along the axial dynamic cold expansion method could get more even than the static methods of residual stress,therefore,the fatigue life of the open hole structure is improved.