Investigation into the fundamentals of contact mechanics in turbine blades roots to enable improved techniques for design optimisation and reliability

In a turbofan engine a large number of metal on metal contacts are present at the base of the fan blades. Theses contacts are subject to varying loads, both due to thermal effects and resulting from vibrations present with the engine; under these conditions a damage phenomenon known as fretting fatigue can occur. Understanding processes and conditions that lead to material degradation and crack initiation is crucial to accurately predict the lifetime of engine components, and to ensure safety in engine design. The overall goal of this work is to advance the understanding of contact mechanics in turbine blade roots to enable improved techniques for design optimisation and life prediction via enhanced understanding of the stress-state in the vicinity of the contact.

The project will be complementary to the fundamental contact research being undertaken by Rolls-Royce plc as part of their Cornerstone research project and will incorporate work on contacts at a fundamental level but will also consider features specific to turbine components.

A part of this project will involve an experimental investigation into the effect of various parameters on the expected lifespan of a contact. Parameters to be considered for testing include; material orientation effects in single crystal materials, contact geometry (flat/barrelled), local geometry effects (e.g. proximity of stress raisers such as notches or corners) & temperature. Many of these contact properties (such as material orientation effects and local geometry effects) have not previously been studied in any depth in the context of fretting fatigue, and as such their effects are currently poorly understood. The test results will be used to advance understanding of the fundamental mechanics and the influence of the parameters investigated.

The other part of this project will be analytical in nature; informed by the results of the experiments numerical and analytical models will be developed to model the state of stress and expected lifetime of the contact. Methods employed in modelling the contact pressure, shear traction and their associated stress fields may include; The use of Finite element software, The Distributed dislocation technique, Direct analytical solutions and the use of asymptotic stress fields. These methods will require modification from their standard forms to allow for the effects being investigated.

This project falls within the EPSRC engineering Theme and is related to the Materials Engineering - Metals & Alloys research area.