Abstract
Turbine blades for thermal power plants are exposed to severe environments, making it necessary to ensure safety against damage, such as crack formation. A previous method detected internal cracks by applying a small load to a target member. Changes in the surface properties of the material were detected before and after the load using a digital holographic microscope and a digital height correlation method. In this study, this technique was applied in combination with finite element analysis using a 2D and 3D model simulating the turbine blades. Analysis clarified that the change in the surface properties under a small load varied according to the presence or absence of a crack, and elucidated the strain distribution that caused the difference in the change. In addition, analyses of the 2D model considering the material anisotropy and thermal barrier coating were conducted. The difference in the change in the surface properties and strain distribution according to the presence or absence of cracks was elucidated. The difference in the change in the top surface height distribution of the materials with and without a crack was directly proportional to the crack length. As the value was large with respect to the vertical resolution of 0.2 nm of the digital holographic microscope, the change could be detected by the microscope.
Highlights
Thermal power generation using gas turbines is expected to expand in the long term as a clean and economical power generation method
These occur under the severe condition of a high temperature, cracks may develop in the cooling passage
We focused on the materials that may be used in the the turbine blade, analysis was performed using was
Summary
Thermal power generation using gas turbines is expected to expand in the long term as a clean and economical power generation method. During the operation of the power plant, the turbine blades are subjected to high centrifugal loads due to the rotation of the rotor, flexural loads due to the working fluid, and vibration loads These occur under the severe condition of a high temperature, cracks may develop in the cooling passage. In order to extend the inspection interval and increase the operation rate by accurately diagnosing the remaining life of the turbine, it is necessary to improve the precision of the inspection method to detect cracks generated in turbine blades in power plants. To meet this requirement, one of the authors has proposed a new flaw detection method using digital holographic microscopy (DHM).
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