Analysis of Loading and Vibration Histories on Natural Frequencies and Modal Damping of Blades With Friction at Root Contact Interfaces

Gas turbine engines change the rotation speed during operation in a wide range from zero to the speed corresponding to the cruise flight and the history of the rotation speed variation is individual for each flight. During the engine operation the bladed disks pass different resonances frequencies and may experience significant vibration amplitudes. The vibrations can affect the interaction conditions at friction contact interfaces, including contact stresses distribution and their contact status. As a result, the contact conditions can differ from those that are established at the initial bladed disk assembling and these conditions are dependent on the history of the vibration that a bladed disk experiences during every engine operation cycle. The variation of the contact conditions at friction contact interfaces affects modal properties and modal damping characteristics of a bladed disk, and it is important to assess the possible variation of these properties during the engine exploitation. In this paper, a transient analysis is performed to simulate blade vibration under different loading histories occurred in a flight mission. The analysis is performed for different histories of the blade vibration and a method is proposed for the analysis of modal damping in the blade root joints under the influence of different loading histories. The influence of different loading histories, friction contact parameters, the vibration excitation levels and resonating modes on modal characteristics and modal damping factors is studied, The pre-stress effects due to blade assembling are also explored.