Improved analytical modeling and characterization of turbine blade friction dampers

This thesis discusses a new approach for characterizing the dynamic behavior of a turbine blade friction damper and how to integrate it into an analysis for predicting the vibratory response of frictionally damped turbine blades.; A prototype damper with a spherical head was manufactured and tested under quasistatic conditions for a range of normal loads and displacements. The data from the resulting friction force, displacement hysteresis curves were processed in order to determine the damper's effective nonlinear damping and stiffness as a function of the amplitude of the motion across the friction interface. The curves are non-dimensionalized and compared with those currently used by industry. Significant differences exist between the behavior of dampers as measured in the laboratory and that often assumed in the models used by industry.; A theoretical model that predicted the damper's behavior was also developed. Mindlin's analysis of a sphere on a half space is used to estimate the friction damper's contact stiffness and its hysteresis curves. The hysteresis curves are then used to predict the damper's nonlinear stiffness and damping curves. The results compare favorably with those found experimentally in the laboratory.; The quasi-static analysis of the spherical damper using Mindlin's theory was then integrated into a dynamic analysis that predicts the vibratory response of frictionally damped blades. The approach was corroborated by conducting vibration tests using a blades/damper test fixture. There was good agreement between the theoretical predictions of amplitude and the values that were measured experimentally over a wide range of test conditions. It is concluded that it is possible to predict the vibratory response of frictionally damped vibrating systems using continuum mechanics provided the contact geometry is clearly defined and the local nonlinear contact is correctly taken into account.