The Effects of Load Ratio on Threshold Fatigue Crack Growth of Aluminum Alloys

...................................................................................................... ii DEDICATION .................................................................................................. iv ACKNOWLEDGEMENTS .............................................................................v LIST OF FIGURES ...........................................................................................x LIST OF TABLES ........................................................................................ xxii NOMENCLATURE ..................................................................................... xxiii PART I – Introduction and Objectives ................................................1 CHAPTER 1 – INTRODUCTION .............................................................2 1.1 – INTRODUCTION TO FATIGUE CRACK GROWTH ..................................2 1.2 – FATIGUE CRACK GROWTH BEHAVIOR OF ENGINEERING METALS ....................................................................................................3 1.3 – DAMAGE TOLERANT DESIGN .................................................................4 1.4 – FATIGUE CRACK GROWTH LOAD RATIO EFFECTS ............................5 1.5 – PROBLEM STATEMENT ............................................................................6 1.6 – LITERATURE REVIEW ...............................................................................7 1.6.1 – Threshold testing procedures .................................................................7 1.6.2 – Fatigue crack closure .............................................................................8 1.6.3 – Closure-free load ratio effects ...............................................................8 1.6.4 – Short crack issues ................................................................................10 1.6.5 – Other influences to consider ................................................................12 CHAPTER 2 – RESEARCH MOTIVATION, OBJECTIVES, AND APPROACH ..............................................................................13 2.1 – MOTIVATION FOR RESEARCH ..............................................................13 2.2 – RESEARCH OBJECTIVES ........................................................................14 2.3 – TECHNICAL APPROACH .........................................................................16 2.4 – PITFALLS TO AVOID ...............................................................................17 PART II – Research ...................................................................................18 CHAPTER 3 – FATIGUE CRACK CLOSURE MODEL ................19 3.1 – INTRODUCTION .......................................................................................19 3.2 – MODEL DEVELOPMENT .........................................................................20 3.2.1 – Consideration of RICC and crack meandering .....................................20 3.2.2 – Stress intensity factors .........................................................................21 3.2.3 – Elastic crack face displacements ..........................................................23 3.2.4 – Consideration of crack-tip plasticity and PICC .....................................23 3.2.5 – Consideration of OICC.........................................................................28