Towards a Unified Fatigue Life Prediction Method for Marine Structures

In order to apply the damage tolerance design philosophy to design marine structures， accurate prediction of fatigue crack growth under service conditions is required. Now， more and more people have realized that only a fatigue life prediction method based on fatigue crack propagation （FCP） theory has the potential to explain various fatigue phenomena observed. In this book， the issues leading towards the development of a unified fatigue life prediction （UFLP） method based on FCP theory are addressed. Based on the philosophy of the UFLP method， the current inconsistency between fatigue design and inspection of marine structures could be resolved.This book presents the state-of-the-art and recent advances， including those by the authors， in fatigue studies. It is designed to lead the future directions and to provide a useful tool in many practical applications. It is intended to address to engineers， naval architects， research staff， professionals and graduates engaged in fatigue prevention design and survey of marine structures， in fatigue studies of materials and structures， in experimental laboratory research， in planning the repair and maintenance of existing structures， and in rule development. The book is also an effectwe educational aid in naval architecture， marine， civil and mechanical engineering.

1 Introduction 1.1 Fatigue Problems in Marine Structures 1.2 Current Practices of Fatigue Strength Assessments and TheirDeficiencies 1.3 Historical Overview of Metal Fatigue 1.4 FLP Methods 1.4.1 CFD Theories 1.4.2 FCP Theories 1.5 The Layout of the Book References2 Current Understanding of Fatigue Mechanisms of Metals 2.1 Introduction 2.2 Different Phases of the Fatigue Life 2.3 Crack Initiation Mechanisms for Different Metals 2.3.1 Definition of a Crack Initiation 2.3.2 Fatigue Crack Initiation in Slip Bands 2.3.3 Crack Initiation Along the Grain Boundary (GB) 2.3.4 Crack Initiation at Inclusions 2.3.5 Slip Band and Dislocation in Single Crystal Metal 2.3.6 Slip Band and Dislocation in Polycrystal Metal 2.3.7 Fatigue Mechanism of Ultrafine-Grained Materials 2.4 FCP Mechanisms 2.4.1 Stage I FCP 2.4.2 Stage II Crack Growth and Fatigue Striation 2.5 Some Important Issues in Crack Growth 2.5.1 Short Crack 2.5.2 Crack Closure 2.5.3 Effect of Loading Sequence 2.5.4 Surface Effects 2.5.5 Environmental Effects 2.6 Fatigue Crack Growth Mechanism of Small Defects 2.6.1 Engineering Initial Crack Size of Structures 2.6.2 Definition of Short Crack and Long Crack 2.6.3 Crack Growth Threshold and Intrinsic Crack Length 2.6.4 Equivalent Crack Length for Short and Long Crack 2.7 Summary References3 Current State-of-the-Art of UFLP 3.1 Introduction 3.2 Unified Approach for Three Regions of FCP 3.3 Unified Approach to the Stress Ratio Effect or Mean Stress Effect 3.4 Unified Approach for Long- and Physically Short-Crack Growth 3.5 Unified Approach for Initiation and Propagation 3.6 Unified Approach for High and Low Cycle Fatigue 3.7 Unified Approach for Fatigue and Creep 3.8 Basic Ideas of Our UFLP Method 3.9 Summary References4 Basic Concepts of Fracture Mechanics 4.1 Introduction 4.2 Type's of Cracks 4.3 Types of Opening Modes for a Cracked Body 4.4 SIFs 4.4.1 Definition 4.4.2 Calculation Methods of SIFs 4.4.3 Typical Examples of SIFs 4.4.4 Plasticity Limitations of the SIFs Based on LEFM 4.4.5 Extensions of the SIFs Based on LEFM 4.5 Fracture Toughness 4.5.1 Definition 4.5.2 Testing 4.5.3 Trends 4.6 Crack Tip Plasticity 4.6.1 Plastic Zone for Plane Stress 4.6.2 Plastic Zone for Plane Strain 4.6.3 Plastic Zone Under Real Stress State 4.7 Summary References5 Development of a UFLP Method for Marine Structures 5.1 Introduction 5.2 A General Procedure for the UFLP Method 5.2.1 The General Function Format of the Fatigue Crack Growth Rate Curve for the UFLP Method 5.2.2 Calculation of Fatigue Life 5.3 Development of a Unified Fatigue Crack Growth Rate Model 5.3.1 The Crack Growth Rate Model for Constant Amplitude Loading 5.3.2 The Improved Crack Growth Rate Model Under VA Loading 5.3.3 Establishment of Cycle-by-Cycle Integration Procedure 5.3.4 Discussion of Model Parameters 5.4 Engineering Approaches to Determine the Parameters in the Improved Model 5.4.1 General Methods to Estimate the Model Parameters 5.4.2 Estimation Method from Crack Growth Rate Data 5.4.3 Estimation Method from a-N Curve 5.4.4 Estimation Method from S-N Curve 5.4.5 Estimation Method from e-N Curve 5.4.6 Estimation Methods from Available Static Test Properties 5.4.7 Estimation of A and m 5.5 Capabilities of the UFLPMethod 5.5.1 The Quantitative Analysis of the Improved Crack Growth Rate Model 5.5.2 Model Validation by Test 5.6 Summary References6 Description of Fatigue Loading 6.1 The Nature of Fatigue Loading 6.2 Load Spectra for CFD Analysis 6.3 Generating the Whole Life Loading History from Short Time Measurement 6.3.1 Method for Extrapolation of a Load History 6.3.2 Choice of Threshold Levels 6.3.3 Examples of Extrapolation of Load Histories 6.4 Cycle Count Methods 6.4.1 Definitions 6.4.2 Rainflow Cycle Counting 6.4.3 A Practical Example 6.5 SLHs for FCP Analysis 6.5.1 Definition 6.5.2 History 6.5.3 Basis of Generation of SLHs 6.5.4 Generation of Load-Time Histories 6.6 Generating a Pseudo Random Loading History from a Spectra 6.7 Summary References7 Some Applications and Demonstrations of UFLP 7.1 Introduction 7.2 The Fatigue Crack Growth Rate of UFLP 7.3 FLP of Specimen with Through-Thickness Crack Under Different Fatigue Loading 7.3.1 FLP of DI 6 Aluminum Alloy Specimens Under Different Spectrum Loading 7.3.2 FLP of Aluminum Alloy A1 7075-T6 7.3.3 FLP of Specimen Made of 350WT Steel Under Different Overload Ratios 7.3.4 The Fatigue Crack Growth Prediction of Steel HTS-A Under Multi-Level Block Loading 7.4 FLP of Cracked Deck of an Oil Tanker 7.4.1 Geometry of the Stiffened Plate 7.4.2 The Crack Growth Pattern in the Stiffened Plate 7.4.3 Determination of SIFs of the Cracked Stiffened Plate by FEA 7.4.4 SIF of the Crack in Stiffened Plate by Weld Residual Stress 7.4.5 Fatigue Crack Growth Prediction of the Stiffened Plate 7.5 FLP of Submarine Hull Under Different Fatigue Loading Sequence 7.5.1 General Equations for Calculating the SIF of a Surface Crack at Welded Toe 7.5.2 SIF of Surface Crack Caused by Weld Residual Stress at Weld Toe 7.5.3 Fatigue Crack Growth Prediction of Surface Crack at Weld Toe of Submarine Structure 7.6 Summary References8 Code Development Based on UFLP for Marine Structures 8.1 Introduction 8.2 Procedure of UFLP 8.3 Fatigue Loading 8.3.1 Simplified Fatigue Loading Analysis 8.3.2 Fatigue Loading by Direct Calculation 8.4 SIF Calculation 8.4.1 Planar Flaws and Their Initial Size 8.4.2 SIF Range Calculation 8.5 Fatigue Crack Growth Law of UFLP for Marine Structural Materials 8.5.1 Recommended Fatigue Crack Growth Material Constants for Steels in Marine Environment 8.5.2 Simplified Fatigue Crack Growth Law and Threshold (BS7910) 8.6 SummaryAppendix A: SIF Solutions for Some Typical CracksReferencesIndex