Acoustic Emission Testing of Highly Loaded Combustor Liner Tiles for Gas Turbines

The redistribution of internal stresses in a material, e.g. as a consequence of mechanical loading, causes the emission of acoustic waves, which are called acoustic emission (AE). The detection of acoustic emission is a common non-destructive testing method and mainly used in pressure vessel testing and structural health monitoring of large structures as e.g. bridges. In this paper the application of acoustic emission testing (AET) to combustor liner tiles (CLT) of gas turbines is presented. These combustor tiles are exposed to thermal cycles under engine-like conditions while acoustic emission testing is applied. A thermal cycle consists of dwell times at low and high temperatures, and heating and cooling phases. The paper first presents basic knowledge of acoustic emission testing and of the experimental rig at the "Institut fir Thermische Stromungsmaschinen (ITS)". Then the adaptation of the measurement technique to the hot combustor environment, which is done by so-called waveguides, is elucidated. Finally some test data are given, which confirm the capability of AET for online damage detection in the thermally loaded CLT. These data show not only a correlation between AE and individual phases of the thermal cycles but allow also a planar localisation of the acoustic emission sources on the CLT.