High-fidelity calculation of modal damping caused by friction at blade roots for single blades and tuned bladed disc assemblies

A method for the analysis of amplitude-dependent modal damping factors is developed for the cases when the energy dissipation is caused by the micro-slip motion at friction contacts of blade root joints. The modal damping at root joints for a lone blade and for tuned bladed disc assemblies is studied. Large three-dimensional finite element models and detailed description of friction contacts by surface-to-surface friction contact elements at contact interfaces of the root joints are used for the calculations. The method allows using available finite element packages and is based on the direct calculation of the energy dissipated at root joints for prescribed levels of vibration amplitudes. The method takes into account the nonlinear dependency of the modal damping factors on the vibration level. The numerical studies of the dependency of modal damping factors on the vibration amplitudes, rotation speed, and contact interface parameters are performed for different families of modes and different nodal diameter numbers.