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Title: On the validation of nonlinear dynamic models for structures with frictional joints
Author: Pesaresi, Luca
ISNI:       0000 0004 7969 8156
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2017
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High cycle fatigue caused by dynamic stresses is one of the main threats for aeroengine components. Friction damping is regularly being used as a passive system to dissipate the vibrational energy of these components. Due to the presence of friction contacts, the dynamic behaviour of engine components becomes nonlinear, making an analysis much more challenging. Various modelling approaches have been proposed, however due to the complexity of the systems, a standard fully validated approach is still not available. This research introduces a detailed explicit modelling approach, based on Imperial College long standing experience with nonlinear dynamic modelling, which has been extended, refined and fully validated for the predictions of the dynamic behaviour of structures with frictional joints. The main focus of this research is on the modelling of underplatform dampers, due to their importance to reduce the vibration amplitudes of turbine blades. A new underplatform damper test rig was designed for this scope, and the tests performed highlighted its ability to reproduce the nonlinear effects caused by the dampers on the blades dynamics often observed in real engines. The explicit modelling approach was then validated against the experimental results of the new rig, providing new insights and guidelines for a state of art damper model. A successful application of the explicit modelling approach to a beam with a frictional bolted joint further demonstrated the versatility of the approach. Nonlinear model validation was then further extended to the local contact behaviour by developing suitable techniques which allow to monitor the stick-slip-separation. Two techniques, one based on high speed camera and digital image correlation, and the other one based on ultrasounds, were proposed and tested, showing a promising potential to provide additional understanding of the contact mechanism at work.
Supervisor: Schwingshackl, Christoph ; Hoffman, Norbert Sponsor: Rolls-Royce Group plc
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral