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Fatigue Life Analyses of Welded Structures

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Avoiding or controlling fatigue damage is a major issue in the design and inspection of welded structures subjected to dynamic loa... Weiterlesen
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Avoiding or controlling fatigue damage is a major issue in the design and inspection of welded structures subjected to dynamic loading. Life predictions are usually used for safe life analysis, i.e. for verifying that it is very unlikely that fatigue damage will occur during the target service life of a structure. Damage tolerance analysis is used for predicting the behavior of a fatigue crack and for planning of in-service scheduled inspections. It should be a high probability that any cracks appearing are detected and repaired before they become critical.  In both safe life analysis and the damage tolerance analysis there may be large uncertainties involved that have to be treated in a logical and consistent manner by stochastic modeling.
This book focuses on fatigue life predictions and damage tolerance analysis of welded joints and is divided into three parts. The first part outlines the common practice used for safe life and damage tolerance analysis with reference to rules and regulations. The second part emphasises stochastic modeling and decision-making under uncertainty, while the final part is devoted to recent advances within fatigue research on welded joints. Industrial examples that are included are mainly dealing with offshore steel structures. Spreadsheets which accompany the book give the reader the possibility for hands-on experience of fatigue life predictions, crack growth analysis and inspection planning. As such, these different areas will be of use to engineers and researchers.

Tom Lassen is from Agder University College in Grimstad, Norway. He also teaches aircraft maintenance for the Norwegian Royal Air Force and has recently been a visiting Professor at University Blaise Pascal, Clermont-Ferrand, France.

Naman Recho has worked extensively with conceptual and applied aspects of fracture mechanics, with welded offshore structures and reliability analysis of cracked structures. He also teaches at Centre des Hautes Etudes de la Construction, Paris, and is guest Professor at Hefei University of Technology in China.


Abbreviations xv

PART I. Common Practice 1

Chapter 1. Introduction 3

1.1. The importance of welded joints and their fatigue behavior 3

1.2. Objectives and scope of the book 4

1.3. The content of the various chapters 5

1.4. Other literature in the field 7

1.5. Why should the practicing engineer apply reliability methods? 8

1.6. How to work with this book 9

1.7. About the authors 10

Chapter 2. Basic Characterization of the Fatigue Behavior of Welded Joints 11

2.1. Introduction and objectives 11

2.2. Fatigue failures 11

2.3. Basic mechanisms of metal fatigue 15

2.4. Parameters that are important to the fatigue damage process 17

2.4.1. External loading and stresses in an item 17

2.4.2. Geometry, stress and strain concentrations 19

2.4.3. Material parameters 20

2.4.4. Residual stresses 24

2.4.5. Fabrication quality and surface finish 25

2.4.6. Influence of the environment 25

2.5. Important topics for welded joints 26

2.5.1. General overview 26

2.6. Various types of joints 30

2.6.1. Plated joints 30

2.6.2. Tubular joints 34

2.7. References 35

Chapter 3. Experimental Methods and Data Analysis 37

3.1. Introduction and objectives 37

3.2. Overview of various types of tests 38

3.3. Stress-life testing (S-N testing) of welded joints 38

3.3.1. Test specimens and test setup 38

3.3.2. Preparations and measurements 41

3.3.3. Test results 46

3.4. Testing to determine the parameters in the strain-life equation 49

3.5. Crack growth tests guidelines for test setup and specimen monitoring 50

3.6. Elementary statistical methods 55

3.6.1. Linear regression analyses 55

3.7. References 60

Chapter 4. Definition and Description of Fatigue Loading 61

4.1. Introduction and objectives 61

4.2. Constant amplitude loading 62

4.3. Variable amplitude loading 63

4.3.1. Overview 63

4.3.2. Rain-flow cycle counting of time series 64

4.3.3. The energy spectrum approach 69

4.4. References 73

Chapter 5. The S-N Approach 75

5.1. Introduction and objectives 75

5.2. Method, assumptions and important factors 76

5.2.1. Statistics for the S-N approach, median and percentile curves 76

5.2.2. Discussion of S-N curves-important factors 78 The threshold phenomenon 78 Mean stress and loading ratio 79 Stress relieving 79 The thickness effect 80 Misalignment 81 Post-weld improvement techniques 82 Corrosive environment 83

5.3. Mathematics for damage calculations 84

5.3.1. Linear damage accumulation; load spectrum on a histogram format 84

5.3.2. Discussion of the validity of the linear damage accumulation 86

5.3.3. Definition of the equivalent stress range 88

5.3.4. Load spectrum on the format of a Weibull distribution 88

5.4. S-N curves related to various stress definitions 91

5.4.1. Nominal stress, geometrical stress and weld notch stresses 92

5.4.2. Geometrical stresses in tubular joints 96

5.4.3. Fatigue life estimate based on the weld notch stress approach 98

5.4.4. Conclusions on the various stress approaches 101

5.5. Some comments on finite element analysis 104

5.6. Current rule and regulations 110

5.6.1. General considerations 110

5.6.2. The original fatigue classes and S-N curves from DoE 112

5.6.3. S-N life predictions according to Eurocode 3-Air environment 117

5.6.4. S-N life predictions according to HSE 119

5.6.5. S-N life predictions according to NORSOK and DNV 120

5.6.6. S-N life predictions for ship structures 122

5.7. The industrial case: an offshore loading buoy 130

5.8. References 136

Chapter 6. Applied Fracture Mechanics 139

6.1. Introduction 139

6.2. Objectives of this chapter 142

6.3. Basic concepts of linear elastic fracture mechanics 142

6.3.1. The local stress field ahead of the crack front 142

6.4. Fracture criterion due to extreme load 152

6.4.1. Mixed mode rupture 153

6.4.2. The R6 criterion and critical crack size 154

6.5. Fatigue threshold and fatigue crack growth 156

6.5.1. Crack growth models 156

6.5.2. Parameters C and m 159

6.5.3. Residual stresses 160

6.5.4. Some notes on the size of the initial cracks 161

6.6. Geometry function and growth parameters given in BS7910 161

6.6.1. The geometry function 162

6.6.2. Parameters C and m 163

6.7. Fracture mechanics model for a fillet welded plate joint 165

6.7.1. Basic assumptions and criteria for the mod...


Titel: Fatigue Life Analyses of Welded Structures
Untertitel: Flaws
EAN: 9780470394793
ISBN: 978-0-470-39479-3
Digitaler Kopierschutz: Adobe-DRM
Format: E-Book (pdf)
Herausgeber: Wiley-Iste
Genre: Sonstiges
Anzahl Seiten: 407
Veröffentlichung: 05.01.2010
Jahr: 2010
Untertitel: Englisch
Dateigrösse: 5.6 MB