Ultrasonically stimulated thermography for crack detection of turbine blades

The hot gas components in a gas turbine have to withstand extreme loads. As failure of turbine blades could have catastrophic consequences, the integrity of the entire engine must always be guaranteed, hence quick and reliable structural health monitoring (SHM) or nondestructive testing techniques (NDT) are essential. In this work, an ultrasonic stimulated thermographic test system was developed to efficiently detect cracks in turbine blades. The used technique is based on the ultrasound excitation with a piezo actuator, where the contact surfaces of the crack are excited and generate frictional heat, which is captured by a thermal imaging camera. A method was developed, where the temperature increase is measured as a function of the electrical energy supply to the actuator. This allows understanding crack topology and the prediction of preloads in the crack. Numerical analysis were conducted for optimising the frequency to be excited for the type of damage experienced by the blade and for understanding the basic physics of the coupling between cracks configuration, local crack velocity and temperature increase. The procedure presented helps to efficiently detect cracks and to optimize the inspection cycles of these components.