The primary goal of the development project was to demonstrate the feasibility of detecting changes in blade bending natural frequencies (such as those asosciated with a blade crack) on a turbine using non-contact, non-intrusive measurement methods. The approach was to set up a small experiemntal apparatus, develop a torsional vibration detection systems, and maximize the dynamic range and the signal to noise ratio. The results of the testing and analysis dlearly demonstrated the feasibility of using torsional vibration to detect the change in natural frequency of a blade due to a change in stiffness such as those asosciated with a blade crack. However, it was found that harmonics of shaft operating speed, created as an unwanted artifact of the measurement method, resutled n spectral regions in which the effective dynamic range was inadequate to detect low-level torsional vibration associated with the natural frequencies.
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