Modeling of Microslip Friction and Its Application in the Analysis of Underplatform Damper

This paper presents a theoretical model for analyzing the damping effect of underplatform dampers for turbine blades. At first, tangential and normal contact stiffness of the friction damper were studied based on a flat-to-flat contact model. The analytic expressions of contact stiffness were presented. Then, a microslip model was developed, and the frictional hysteresis loops were obtained by the Masing hypothesis. The so-called "B-B" (Blade to Blade) model was studied in this paper, and both cylindrical and wedge-shaped dampers were calculated in the case studied. The inertia and rotating effect of the damper were ignored for simplicity. Thus, the damper's motion between blade platform locations could be determined by iteration of force balance equations of the damper once the blades' motions as inputs of the system were determined. The effect of normal load on the contact stiffness was ignored for simplicity. The friction force was linearized by harmonic balanced method, considering only the first-order harmonic terms. Finally, the relationship between damping ratio and the maximum vibration stress of the blades was calculated to assess the damping effect of the damper.