Structural Hot-Spot Stress Approach to Fatigue Analysis of Welded Components (eBook)

Erkki Niemi is Emeritus Professor of Steel Structures in Lappeenranta University of Technology, Finland. Wolfgang Fricke is Professor (retired) of the Institute for Ship Structural Design and Analysis at Hamburg University of Technology, Germany. Stephen J. Maddox is a Consultant with The Welding Institute (TWI) in the UK and is also Visiting Professor in the Department of Mechanical Engineering at the University of Strathclyde, UK.

Preface 6
Contents 9
Abstract 13
1 Introduction 14
1.1 General 14
1.2 Safety Aspects 16
References 16
2 The Structural Hot-Spot Stress Approach to Fatigue Analysis 18
2.1 Field of Application 18
2.2 Types of Hot Spot 19
2.3 Definition of the Structural Stress at a Type “a” Hot-Spot 20
2.4 Use of Stress Concentration Factors 22
2.4.1 Modified Nominal Stress 22
2.4.2 Structural Stress Concentration Factors, Ks 22
2.4.3 Stress Magnification Factor Due to Misalignment Km 23
2.5 Effect of Component Size on the Fatigue Resistance 25
References 25
3 Experimental Determination of the Structural Hot-Spot Stress 26
3.1 General 26
3.2 Type “a” Hot Spots 26
3.3 Type “b” Hot Spots 28
References 29
4 Structural Hot-Spot Stress Determination Using Finite Element Analysis 30
4.1 General 30
4.2 Choice of Element Type 31
4.3 Methods for Determination of Structural Hot-Spot Stress 32
4.3.1 Determination of the Structural Stress at the Weld Toe Using Through-Thickness Linearization 33
4.3.2 Determination of the Structural Stress at the Weld Toe Using Surface Stress Extrapolation 34
4.3.3 Determination of the Structural Stress at a Single Point Close to the Weld Toe 38
4.4 Use of Relatively Coarse Element Meshes 39
4.4.1 Solid Element Modelling 39
4.4.2 Thin Shell (or Plate) Element Modelling 40
4.4.3 Hot-Spot Stress Extrapolation 40
4.5 Use of Relatively Fine Element Meshes 41
4.5.1 Solid Element Modelling 41
4.5.2 Thin Shell (or Plate) Element Modelling 42
4.5.3 Hot-Spot Stress Extrapolation 42
4.6 Modelling Fillet Welds in Shell Element Models 42
References 43
5 Parametric Formulae 45
5.1 Misalignment 45
5.1.1 Axial Misalignment Between Flat Plates of Equal Thickness Under Axial Loading 45
5.1.2 Axial Misalignment Between Flat Plates of Differing Thickness Under Axial Loading 46
5.1.3 Axial Misalignment Between Tubes or Pipes Under Axial Loading 46
5.1.4 Axial Misalignment at Joints in Pressurized Cylindrical Shells with Thickness Change 47
5.1.5 Angular Misalignment Between Flat Plates of Equal Thickness Under Axial Loading 47
5.1.6 Angular Misalignment at Longitudinal Joints in Pressurized Cylindrical Shells 48
5.1.7 Ovality in Pressurized Cylindrical Pipes and Shells 49
5.2 Structural Discontinuities 49
References 50
6 Structural Hot-Spot S-N Curves 51
6.1 General Principles 51
6.2 Recommended S-N Curves for the Conventional Structural Hot-Spot Stress Approach 54
6.2.1 Hot-Spot S-N Curves 54
6.2.2 Hot-Spot S-N Curves for Tubular Joints in Steel 55
6.3 Recommended S-N Curves for the Other Structural Stress Approaches 55
6.3.1 Structural Stress Approach According to Dong 55
6.3.2 Structural Stress Approach According to Xiao and Yamada 56
6.3.3 Structural Stress Approach According to Haibach 56
References 56
7 Case Study 1: Box Beam of a Railway Wagon 58
7.1 Introduction 58
7.2 Materials and Methods 58
7.2.1 Description of the Structure 58
7.2.2 Angular Misalignment in the Web 58
7.2.3 Strain Gauge Measurements 59
7.2.4 Structural Hot-Spot Stress Determination 60
7.2.5 S-N Curve 61
7.2.6 Partial Safety Factors 62
7.3 Results 62
7.3.1 Stress Concentration Factor, Ks 62
7.3.2 Results for a Perfectly Straight Web 62
7.3.3 Effective Magnification Factor, Km 63
7.3.4 Results for a Web with Angular Misalignment 64
7.4 Discussion and Conclusions 64
8 Case Study 2: Hatch Corner Design for Container Ships 66
8.1 Introduction 66
8.2 Materials and Methods 66
8.2.1 Description of the Structure 66
8.2.2 Service Loads 66
8.2.3 Experimental Investigation 67
8.2.4 Structural Hot-Spot Stress Determination 68
8.2.5 S-N Curve Based on Nominal Stress 69
8.3 Fatigue Assessment 70
8.4 Conclusion 70
Reference 70
9 Case Study 3: Web Frame Corner 71
9.1 Introduction 71
9.2 Computation of the Structural Hot-Spot Stress 72
9.2.1 Finite Element Modelling 72
9.2.2 Computation of Structural Hot-Spot Stresses 73
9.3 Fatigue Tests 74
9.3.1 Performance of the Tests 74
9.3.2 Observed Fatigue Lives 74
9.3.3 Comparison with Design S-N Curves 75
Reference 76
10 Case Study 4: Loaded Stiffener on T-Bar 77
10.1 Introduction 77
10.2 Computation of the Structural Hot-Spot Stress 77
10.2.1 Finite Element Modelling 77
10.2.2 Determination of the Structural Hot-Spot Stress by Extrapolation 79
10.2.3 Determination of the Structural Stress According to Dong 80
10.2.4 Determination of the Structural Stress According to Xiao/Yamada 82
10.3 Estimation of the Design Fatigue Life 82
10.3.1 Fatigue Life Determined from Extrapolated Stress 82
10.3.2 Fatigue Life Determined from Dong’s Approach 82
10.3.3 Fatigue Life Determined from Xiao/Yamada’s Approach 83
10.3.4 Comparison with Test Results 83
References 83
Appendix 84
Symbols 84