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

在涡扇发动机中，风扇叶片的底部存在大量的金属对金属接触。这些触点会受到不同的负载，既有热效应，也有发动机振动所致；在这些情况下，可能会发生一种称为微动疲劳的损坏现象。了解导致材料降解和裂纹萌生的过程和条件，对于准确预测发动机部件的寿命，确保发动机设计的安全性至关重要。这项工作的总体目标是促进对涡轮叶片根部接触机理的了解，通过增强对接触附近的应力状态的了解来改进设计优化和寿命预测的技术。该项目将补充劳斯莱斯公司正在进行的基础接触研究，作为其基石研究项目的一部分，并将纳入基础水平上的接触工作，但也将考虑涡轮组件的特定特征。该项目的一部分将涉及各种参数对接触预期寿命的影响的实验调查。要考虑的测试参数包括：单晶材料中的材料取向效应、接触几何形状(平面/桶形)、局部几何形状效应(例如，凹槽或拐角等应力提升器的接近程度)和温度。许多这些接触特性(如材料取向效应和局部几何效应)以前没有在微动疲劳的背景下进行任何深入的研究，因此，目前对它们的影响知之甚少。试验结果将被用来促进对基本力学和所研究参数的影响的理解。本项目的另一部分将是分析性的；根据试验结果，将开发数值和分析模型来模拟接触的应力状态和预期寿命。模拟接触压力、剪切牵引力及其相关应力场的方法包括：使用有限元软件、分布位错技术、直接解析法和使用渐近应力场。这些方法将需要对其标准形式进行修改，以允许研究效果。本项目属于EPSRC工程主题，与材料工程-金属和合金研究领域相关。

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.