NDTnet 1998 Aug, Vol.3 No.8

Abstract

Gas turbine blades and vanes are operating in a high temperature and corrosive atmosphere . Due to this the lifetime is limited. In order to increase the lifetime different measures are applied. One important step is either to cast or to drill cooling channels into the blades or vanes. The remaining wallthickness between cooling channels and blade/vane surface is of great interest regarding the cooling function as well as the stability of blades and vanes. A full automatic infrared system has been developed to inspect the whole shape of a blade and if necessary to calculate the wallthickness at the point of interest. Based on the 1-dimensional differential equation of heat flow a solution is given, where two special parameters identify the wallthickness. After heating the material with a short heat pulse by flashlamps, the time-dependent surface temperature is recorded by an infrared camera. A curvefit function uses a gradient-expansion algorithm to compute a non-linear least squares fit to the supplied function with the both parameters.
In addition to the experimental results, the finite element method (FEM) simulates the experimental setup to proof the reliability of this method. The results from a finite elemente modell with the same material properties are compared with real dates. Complex specimens show the influence of the 2-dimensional heatflow. Due to this fact a further developed method show an improvement to calculate the parameters, which are necessary to determine the wallthickness.

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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