铝合金紧固孔复合强化工艺研究

Composite Strengthening Process of Aluminum Alloy Fastener Holes

目的研究激光喷丸-冷挤压复合强化工艺对7050铝合金紧固孔疲劳源、疲劳寿命的影响。方法利用ABAQUS软件进行复合强化工艺的有限元仿真,并在强化后施加循环载荷获得残余应力数据,然后在应力水平为195 MPa、应力比为0.1的条件下进行疲劳实验,并把仿真和疲劳实验的结果与激光喷丸、冷挤压进行对比。结果复合强化工艺能同时对表面和孔壁进行强化,复合强化工艺比激光喷丸表面和孔壁的残余压应力大,循环载荷下两者残余应力的差异减小。冷挤压工艺表面全部是拉应力,循环载荷下挤出面孔角附近的残余应力由-928 MPa变为300 MPa。未处理紧固孔的疲劳源位于孔角处,激光冲击强化紧固孔的疲劳源位于中间孔壁处,冷挤压紧固孔的疲劳源位于挤出面孔角附近,复合强化紧固孔的疲劳源位于中间孔壁处,复合强化紧固孔的疲劳裂纹扩展区面积最大。未处理、激光喷丸、冷挤压、复合强化的紧固孔的疲劳寿命分别为65 918、165 117、114494、225 209。结论与未处理的紧固孔的疲劳寿命相比,激光喷丸、冷挤压、复合强化的紧固孔的疲劳寿命都有所增加,复合强化的紧固孔的疲劳寿命最大,复合强化能够进一步提高紧固孔的疲劳寿命。激光喷丸和复合强化诱导的残余压应力层能够抑制疲劳裂纹萌生于表面,而冷挤压工艺则不能。

The work aims to study the effect of laser shock peening-cold extrusion composite strengthening process（LSP-CP） on fatigue initiation and fatigue life of 7050 aluminum alloy fastener holes. The finite element simulation of CP was conducted with the software of ABAQUS and the cyclic load was applied to obtain the data of residual stress after strengthening. Then the fatigue test was performed with stress level of 195 MPa and stress ratio of 0.1. The results of simulation and fati-gue test were compared with the process of laser shock peening（LSP） and cold extrusion（CP）. The surface and hole wall could be reinforced by LSP-CP and the value of residual compressive stress induced by LSP-CP was higher than that of LSP at these locations. The residual stress difference between LSP-CP and LSP reduced under cyclic load. But for CP, the surfaces were tensile stress, and residual stress around the extruded surface hole corner was changed from-928 MPa to 300 MPa under cyclic load. In addition, fatigue crack of untreated fastener hole initiated at the hole corner. The fatigue crack of fastener hole reinforced by laser shock initiated at the middle hole wall. The extended area of fatigue crack of fastener hole subject to composition reinforcement was the largest. The fatigue lives of untreated hole, LSP-worked hole, CP-worked hole and LSP-CP-worked hole were 65,918, 165,117, 114,494 and 225,209 respectively. Compared with untreated fastener hole, the fatigue lives of LSP-worked hole, CP-worked hole and LSP-CP-worked hole were increased. LSP-CP-worked hole has the longest fatigue life and can further improve the fatigue life of fastener holes. The residual compressive stress layer induced by LSP and LSP-CP can resist the fatigue crack initiated at the surface, while the CP cannot.