Analysis of Nonlinear Modal Damping due to Friction at Blade Roots Using High-Fidelity Modelling

In this paper, a methodology is developed for analysis of modal damping in root joints of bladed discs using large finite element models and detailed description of friction contacts at contact interfaces of the joints. The methods allows the analysis of: (i) a single blade vibration and (ii) a bladed-disc assembly for any family of modes (lower and higher modes) calculating the modal damping factors for different levels of vibrations. Three-dimension solid finite element models are used in the calculations. The analysis is performed in time domain through the transient dynamics analysis. The methodology allows the use of widely available finite element packages and based on the direct calculation of the energy dissipated at root joints due to micro-slip over the multitude of contact elements modelling the surface-to-surface friction contact interactions. The numerical studies of the dependency of modal damping factors on the vibration amplitudes are performed for simplified and realistic bladed disc models for different blade mode shapes, engine-order excitation numbers and nodal diameter numbers using high-fidelity models.