In turbomachinery blading the avoidance of High Cycle Fatigue (HCF) failures is of great importance. The prediction and reduction of vibration amplitudes is of primary objective in context of HCF risk reduction. For this reason the quantification of the mechanical damping is of essential relevance.
During the last decades the research has been focused on the usage of nonlinear calculation tools to predict vibration amplitudes of blades. These calculations require the specification of contact parameters as well as of material damping values. Especially for weakly damped systems like turbine blades, it is necessary to specify adequate structural damping values which determine the accuracy of the calculated transfer function. However, many researchers use uncertain structural damping values to calculate transfer functions.
In this paper, an experimental setup for specimen specific damping determination in a vacuum chamber is presented. Three different clamping mechanisms, as well as the mechanism for specimen excitation, are introduced. A suspended-like specimen clamping, where the specimens are clamped in their nodes of vibration, is described first. To analyze potential influence of the clamping procedure, a comparison is given to specimens clamped on one side (cantilever beams), where the magnitude of the clamping force is chosen in a way that the friction loss is minimized. To allow an application of static stresses the specimens are clamped on both sides in the third approach. The excitation of the analyzed specimens is performed with the help of a voice-coil actuator. Damping values are determined by analyzing the decay curve, which is measured with a laser doppler vibrometer. Further experimental results show the influence of ambient pressure, frequency, amplitude, geometry, mode shape, static stress and clamping mechanism on the specimen specific damping value.
