飞机钛合金接耳孔边激光冲击强化 应力场优化与试验研究

目的 钛合金关键承力接耳孔边疲劳断裂是影响飞机飞行安全的重难点问题，采用激光冲击强化技术对TC4钛合金小孔件进行强化，提高其疲劳寿命。方法 开展TC4钛合金小孔件单点有无填充、多点搭接激光冲击强化有限元数值模拟研究，确定最优强化工艺，并设计带双孔疲劳试样，进行疲劳试验验证。 结果 直径3 mm光斑单点激光冲击强化的有效范围仅为1.9 mm。孔内有填充，最内圈光斑圆心距孔边0.75 mm时，单光斑激光冲击强化孔边残余应力场分布均匀，且不会引入残余拉应力。双面依次强化会使先强化面残余压应力值略高于后强化面。46.5%径向搭接率下，孔边多点搭接激光冲击强化应力场均匀性优于36.5%和56.5%径向搭接率。强化后，试样的疲劳寿命得到提升，提升效果随最大加载力的减小而显著增大。断口分析表明，强化后，孔边裂纹源位置向深度方向移动，疲劳裂纹扩展区的疲劳条带间距明显减小。结论 最优强化工艺为：周向搭接率56.5%，径向搭接率46.5%，最内圈光斑圆心距孔边0.75 mm，孔填充双面同时强化。激光冲击强化在孔边表面引入600~800 MPa的残余压应力，模拟件疲劳寿命提升了6.98%~60.96%。

Stress Field Optimization and Experimental Investigation of Titanium Alloy Lugs in Aircraft by Laser Shock Peening

The work aims to strengthen TC4 titanium alloy with small hole by laser shock peening (LSP) to improve its fatigue life, because the fatigue fracture of the TC4 titanium alloy hole used in the key bearing lugs is a difficult problem affecting the flight safety of the aircraft. FEM numerical simulation of TC4 titanium alloy samples with small hole subjected to single point LSP with or without filler and multi-point lapping LSP was carried out to determine the optimal LSP technology and design double-hole fatigue sample to conduct fatigue test. The effective range of single spot LSP with a diameter of 3 mm was only 1.9 mm. When the hole was filled and the center of the innermost ring laser spot was 0.75 mm away from the edge of the hole, the residual stress field on the surface near the hole was uniformly induced by single spot LSP, and no tensile residual stress was introduced. The value of compressive residual stress of the first strengthened plane was slightly higher than that of the latter strengthened plane, and the uniformity of the stress field of multipoint LSP on the hole edge under 46.5% radial lapping rate was better than 36.5% and 56.5% radial lapping rate. The fatigue life of the sample was improved after LSP, and the strengthening effect dramatically increased with the decrease of the maximum load. The fracture analysis showed that the crack source at the edge of the hole moved toward depth direction after LSP and the distance between the fatigue bands in the crack growth zone decreased significantly. The optimal LSP technology is 56.5% circumferential lapping ratio, 46.5% radial lapping ratio, distance of 0.75 mm between the center of the innermost laser spot and the edge of the hole and the hole filled with filler subjected to both sides LSP at the same time. LSP introduces a compressive residual stress within 600~800 MPa on the surface near the hole, and the fatigue life of the simulated sample increases by 6.98%~ 60.96%.