Volume 10, Issue 1 (January 1982)
Damping in Turbine Blade Alloys
Measurements of the damping capacity Q−1 of candidate turbine blade alloys for the Wairakei, New Zealand geothermal power station and other future power stations are reported. The techniques used were the piezoelectric ultrasonic composite oscillator technique (PUCOT) at 40 or 80 kHz and stress levels 70 kPa to 37 MPa and the vibrating reed technique (VRT) at 321 Hz and stress levels 32 to 177 MPa. Specimen materials investigated were Ti-6A1-4V, 26Cr-1Mo steel, Firth-Vickers (United Kingdom) FV520B steel, 15Cr-Mo steel, and 410 (Unified Numbering System [UNS] S41000) stainless steel. The results include Young's modulus and the stress and strain amplitude dependences of Q−1. The frequency dependence of Q−1 was found to be only a few tens of percent, much smaller than the predicted dependence. Of the two techniques, it was shown that the VRT is more suited to damping measurements at the operational stress levels for turbine blades. The PUCOT, VRT, and high stress cyclic stress-strain data were plotted on a universal curve of damping energy versus stress. The plot covers 14 orders of magnitude in damping energy and five orders in stress.