TC21钛合金板孔冷挤压残余应力与疲劳性能研究

Residual Stress and Fatigue Properties of the Cold Hole Expansion Process in Titanium Alloy TC21 Plates

针对飞机后机身框TC21损伤容限钛合金带孔零件在服役过程中易过早产生疲劳裂纹的问题,采用开缝衬套冷挤压强化工艺进行了不同挤压量下的孔强化实验,并对挤压强化后的试样进行疲劳试验研究,得到了挤压量对TC21钛合金疲劳增益的影响规律。通过有限元仿真的方法研究了挤后孔边残余应力分布规律,从宏观和微观两方面观察和分析了不同挤压量下的疲劳断口形貌,探讨了冷挤压对孔边疲劳裂纹的萌生和扩展的影响,揭示了疲劳增益机理。研究结果表明,冷挤压强化后的孔边存在明显的切向压缩残余应力,改变了孔边裂纹萌生位置,延长了交变载荷作用下的疲劳裂纹扩展寿命,疲劳寿命随着挤压量的增大而明显提高,挤后试样疲劳寿命均提高50%以上。

The perforated parts of damage tolerant titanium alloy TC21 in rear fuselage frame are easy to prematurely suffer fatigue crack in the service process. In order to solve the problem, different expansion degrees were applied to the hole of plate specimens of TC21 in the split sleeve cold expansion experiment. The effect of expansion degree on fatigue life was investigated in the fatigue tests. By 3D finite element simulation, the distribution regularity of residual stress was obtained around the hole after cold expansion. The surface feature of fatigue fracture has been analyzed from macroscopic aspect and microscopic aspect with different expansion degrees. The examination of fractured sections show that cold expansion can change fatigue crack initiation position around the hole surface, and extend the fatigue crack propagation life under cyclic loading. It is further shown that fatigue life increases as expansion degree increases; furthermore, the fatigue life improves by more than 50%.