激光冲击叶片榫头变形控制与疲劳试验

Deformation Control and Fatigue Test of Blade Tenon by Laser Shock Peening

针对某航空发动机涡轮叶片榫头部位疲劳断裂故障,利用激光诱导高压冲击波对榫头部位进行冲击强化,提高其抗疲劳性能。在试验测试激光冲击GH4133B镍基高温合金材料残余应力场的基础上,确定了叶片材料激光冲击工艺参数;根据榫齿面转接R区结构特征,设计了不等强度分布冲击方式,保证强化区域残余应力均匀、过渡分布,防止出现应力突变。由于榫头结构不均匀,高压冲击波引起的塑性流动使叶片发生宏观变形,采用数值仿真方法分析了激光冲击后叶片榫头宏观变形规律和机理。在此基础上提出了激光冲击叶片榫头变形控制的方法,并设计了榫头结合面冲击区域和方式,保证叶片榫头两侧对应区域的激光能量输入基本相当,通过结合面的塑性流动来减小叶片榫头宏观变形。冲击处理后的叶片榫头表面粗糙度、滚棒尺寸和平面度等均满足技术要求。并分析了激光冲击强化提高叶片高温疲劳寿命的原因。疲劳试验结果表明:激光冲击强化可提高叶片榫头部位的高温高低周复合疲劳寿命提高了279%。

The first groove near the transition section of a turbine blade is easy to crack under alternate stresses and high temperature. In order to improve the fatigue strength of the blade, the whole tenon of the blade is treated by a shock wave generated by a high power density laser, which is called laser shock peening. The parameters of the laser shock peening are determined by the results of residual stress obtained in a laser shock peening test. According to the geometrical charac- teristics of the tenon, a varied-intensity shock pattern is designed. The tooth and groove are treated with different power densities in order to generate smooth residual stress distribution and avoid large stress gradient. Because the tenon is not symmetrical, the treated part will be deformed plastically by the high pressure shock wave, which is unsatisfactory for tech- nical requirements, A numerical simulation model with different shock patterns is set up to analyze the deformation mecha- nisms. A method is brought forward to prevent macro deformation. The treated region and manner on the combining surface are determined by the deformation characteristics in different areas to ensure that the laser energy per square millimeter on one side is the same as on the other side. The macro deformation of the tenon is reduced or prevented with the plastic de- formation generated on the combining surface. The surface roughness, characteristic dimension and flatness are within the range of technical requirements. And the causes are analyzed for laser shock peening improving high temperature fatigue performance. It demonstrates that laser shock peening can improve the fatigue life of the blade by about 279%.