Holography as a Routine Method of Vibration Analysis

The application of holography as a routine method of analysing the vibrations in aero-engine compressor and turbine blades and discs is studied to overcome the disadvantages of the usual sand pattern and piezo-electric crystal contact probe methods. The Stetson-Powell time average fringe hologram technique of vibration analysis is used to investigate the nodal patterns of a 3-in and 6-in compressor blade together with those of a 10-in diameter turbine disc and the disc with a full set of blades. Two real time holographic methods of vibration analysis are also studied. The hologram system and apparatus are simplified to enable the normal methods of clamping the vibrating components to be utilized. A completely self-contained unit that is capable of both taking the hologram and photographing the reconstructed image has been developed. The unit is a box-like structure which is simple to operate and can be used in a normal inspection bay environment for objects up to 2 ft diameter.