Experimental Investigation on the Damping Effectiveness of Blade Root Joints

The mechanical design of turbine blades aims at verifying the structural integrity against High Cycle Fatigue damage. For this reason Forced Responses are simulated in order to evaluate the distribution of variable stress in the blade. When resonant excitation can not be avoided in service, the mechanical damping is enhanced to reduce blade vibrations by the design of friction joints which dissipate energy by the slip of the contact surfaces. In this paper a test campaign is presented in order to collect a database of the nonlinear Frequency Response Functions (FRF) of a dummy blade by varying the normal contact load and the amount of excitation of the system. Two different geometries of blade root joints are tested: the dovetail and the crowned joint. Commissioning of the exciter and of the measurement system is described and discussed in order to define the fastest and most reliable FRF measurement.