Subprojekt A1 Non Destructive Characterization of Turbine Blades

High demands on the performance and reliability of modern engines require the integrity of highly stressed engine components such as turbine, compressor and fan blading and their condition assessment during inspections and maintenance. During operation, the blading is exposed to extremely high thermal, corrosive, erosive and mechanical stresses. The components are designed as a component multilayer system according to that stress profile. The base and layer material has to fulfil highest demands required for continuous engine operation. The condition and integrity of engine blading are of strategic importance for engine reliability and operation safety. This places a stringent requirements on non-destructive testing techniques, material characterization and early damage detection.  In order to be able to assess and evaluate a necessary repair requirements for stressed components and thus also be able to take these into account for the planning of the further regeneration path, a fast engine components investigation, which can already be carried out in the partially stripped engine, is becoming increasingly important.

Video: Blisk inspection using induction thermography

The third funding period aims to to develop a mobile and flexible electromagnetic testing system with adapted eddy current sensors, as well as a thermographic testing system with combined inductor mirror optics for defect detection.  The purpose of the development is to evaluate the condition of stator and rotor blades directly at the partially stripped engine. Another subject of the research is the in situ detection and characterization of damage development as well as the changes in material properties under thermal and cyclic loading of regenerated samples and components compared to new parts. The changes in specimen are going to be investigated using a specially designed thermomechanical test rig with combined non-destructive testing techniques like eddy current, thermography and acoustic emission. The use of initially paramagnetic Ni-base materials at high temperatures in a sulfur-containing atmosphere (such as in the exhaust gas stream) leads to significant changes in the magnetic properties due to the local formation of ferromagnetic phases. In order to characterize, quantify and use as a condition indicator of the degree of high-temperature microstructural changes (hot gas corrosion) in turbine blade materials the development of a non-destructive electromagnetic testing technique based on harmonic analysis is planned.