ANALYSIS OF NONLINEAR MODAL DAMPING DUE TO FRICTION AT BLADE ROOTS IN MISTUNED BLADED DISCS

A method is proposed to analyse the modal damping in mistuned bladed-disc with root joints using large finite element models and the detailed description of frictional interactions at contact interfaces. The influence of mistuning on the dissipated energy for different blades on a bladed-disc and the modal damping factors for different vibration levels for any family of modes can be investigated. The dissipated energy and damping factors due to micro-slip are simulated by multitude of surface-to-surface elements modelling the friction contact interactions at root joints. The analysis is performed in the time domain and an original reduction method is developed to obtain the results with acceptable computational times. The model reduction method allows the calculation of the modal damping of the mistuned assembly by evaluation of the energy dissipated at root joint of each individual blade using small parts of bladed disc sectors. The dependency of modal damping factor on blade mode shapes, engine-order excitation numbers, nodal diameter numbers and vibration amplitudes are studied and the distributions of amplitude and dissipated energy on the mistuned bladed-disc are investigated using a realistic blade disc model.