Titanium Ti-6Al-4V

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Table of contents

Contents
1 Introduction
1.1 Context of the study
1.2 The contact problem
1.3 Stress gradient and scale eect
1.4 Thesis scope
2 Literature Review
2.1 Fretting
2.1.1 Introduction
2.1.2 Tribological behaviour of contact
2.1.3 Subsurface stress eld
2.1.4 Numerical modelling of fretting fatigue
2.2 Titanium Ti-6Al-4V
2.2.1 Macrozones of the Ti-6Al-4V alloy
2.2.2 Microstructure and material properties observed in literature
2.3 Fatigue of materials
2.3.1 Basic concepts
2.3.2 Uniaxial tests and inuence of the loading ratio
2.3.3 Criteria based on stress invariants
2.3.4 Critical plane approach
2.3.5 Gradient eect – Local vs Non local approach
2.3.6 Scale eect – Probabilistic approach
2.4 Fracture mechanics
2.4.1 Introduction
2.4.2 Fracture modes
2.4.3 Asymptotic solution
2.4.4 J-integral
2.4.5 Method of distribution of dislocations
2.4.6 Paris Law
2.4.7 The Kitagawa{Takahashi (K{T) diagram
2.4.8 Crack closure or eect of the loading ratio
2.4.9 Gradient eect – Critical distance
2.4.10 T-stress
2.5 Summary of the literature review
3 Test design and experimental protocol
3.1 Introduction
3.2 Apparatus conguration and preliminary test
3.2.1 Pads and Specimen
3.2.2 Experimental set-up used for cylinder-plane fretting fatigue research
3.2.3 Digital Image Correlation applied to fretting fatigue
3.2.4 Experimental set-up for spherical-plane fretting bi-axial fatigue research
3.2.5 Coecient of friction
3.3 Finite element modelling of fretting fatigue tests
3.3.1 Basic 2D model
3.3.2 Comparison with 3D model
3.3.3 Crack modeling
4 Experimental results
4.1 Results of cylinder/plane fretting fatigue test
4.1.1 First set of tests
4.1.2 Comparison among dierent gradients
4.2 Results of spherical/plane fretting fatigue test
4.2.1 Objective
4.2.2 Experimental test realized
4.3 Conclusion of the experimental tests
5 Prediction of fretting fatigue life
5.1 Introduction
5.1.1 Material properties and coecient of friction of Ti-6Al-4V alloy
5.1.2 On the use of the analytical formulation of the contact problem
5.1.3 Location of the critical site for crack initiation
5.2 Multiaxial stress fatigue model
5.2.1 Fretting map and comparison with experimental results
5.2.2 Discussion on the model
5.2.3 Proposition of criterion parameter
5.3 Short crack arrest approach
5.3.1 Introduction
5.3.2 Comparison with experimental results
5.3.3 Eect of the loading ratio
5.3.4 Conclusion
5.4 A new methodology – Using the T-stress
5.4.1 Assumptions
5.4.2 Expression of the criterion
5.4.3 Identication of the parameters
5.4.4 Representation of the criterion
5.4.5 Application to fretting
6 Conclusions, recommendations and future work
6.1 Overview
6.2 Methodology used in this study
6.2.1 Experimental set-up
6.2.2 Analytical and numerical modeling of the problem
6.2.3 Prediction of fretting fatigue lifetime
6.3 Main conclusions
6.3.1 Fretting fatigue experiments
6.3.2 Prediction of the fretting fatigue lifetime
6.4 The scale eect
6.5 Notch analogy