Deformation control and fatigue test of blade tenon by laser shock peening

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 characteristics 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 technical requirements. A numerical simulation model with different shock patterns is set up to analyze the deformation mechanisms. 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 deformation 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%.