Uneven degradation of the material during the operation of turdine blades

Turbine rotor blades operate under the action of centrifugal forces, which create height-varying stresses. The temperature field of the blades is also inhomogeneous, and the value of its gradient depends on the flow parameters and the geometric dimensions of the blades. In the process of manufacturing and quality control of completed turbine rotor blades, the manufacturer uses the generally accepted state standards to determine the condition during long-term operation. It is assumed that the material of the blades should be uniform all over the volume so that the manufacturer proposes analyzing mainly the blade root. In this case, mechanical tests are carried out on large samples and the results provide only averaged data on the state of the material. Life prediction based on the results of mechanical tests can lead to a mistaken overestimation of service life. This is because this approach takes into account only the state of the internal zones of the material. However, the rupture of material occurs on the surface and in the more thermally stressed parts like the trailing edge or leading edge. As a consequence, the application of this approach is unacceptable for blades with long operating time.