Fatigue Analysis of Welded Components

This report provides background and guidance on the use of the structural hot spot stress approach to the fatigue design of welded components and structures. It complements the IIW recommendations for 'Fatigue Design of Welded Joints and Components' and extends the information provided in the IIW recommendations on 'Stress Determination for Fatigue Analysis of Welded Components'. This approach is applicable to cases of potential fatigue cracking from the weld toe. It has been in use for many years in the context of tubular joints. The present report concentrates on its extension to structures fabricated from plates and non-tubular sections.Following an explanation of the structural hot spot stress, its definition and its relevance to fatigue, the authors describe methods for its determination. Stress determination from both finite element analysis and strain gauge measurements is considered. Parametric formulae for calculating stress increases due to misalignment and structural discontinuities are also presented. Special attention is paid to the use of finite element stress analysis and guidance is given on the choice of element type and size for use with either solid or shell elements. Design S-N curves for use with the structural hot spot stress are presented for a range of weld details. Finally, practical application of the recommendations is illustrated in two case studies involving the fatigue assessment of welded structures using the structural hot spot stress approach. - Provides practical guidance on the application of the structural hot-spot stress approach - Discusses stress determination from both finite element analysis and strain gauge measurements - Practical application of the recommendations is illustrated in two case studies

Professor Erkki Niemi is Emeritus Professor of Steel Structures in Lappeenranta University of Technology, Finland.Professor Dr-Ing. Wolfgang Fricke is Head 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
- Abstract
- 1. Introduction - 1.1 General
- 1.2 Safety aspects
- 2. The Structural Hot Spot Stress Approach to Fatigue Analysis - 2.1 Field of application
- 2.2 Types of hot spot
- 2.3 Definition of the structural stress at a Type 'a' hot spot
- 2.4 Use of stress concentration factors
- 2.5 Effect of component size on the fatigue resistance
- 3. Experimental Determination of the Structural Hot Spot Stress - 3.1 General
- 3.2 Type 'a' hot spots
- 3.3 Type 'b' hot spots
- 4. Structural Hot Spot Stress Determination Using Finite Element Analysis - 4.1 General
- 4.2 Choice of element type
- 4.3 Methods for determination of structural hot spot stress
- 4.4 Use of relatively coarse element meshing for analysing Type 'a' hot spots
- 4.5 Use of relatively fine element meshing for analysing Type 'a' hot spots
- 4.6 Modelling fillet welds in shell element models for analysing Type 'a' hot spots
- 4.7 Analysis of Type 'b' hot spots
- 5. Parametric Formulae - 5.1 Misalignment
- 5.2 Structural discontinuities
- 6. Structural Hot Spot S-N Curves - 6.1 General principles
- 6.2 Recommended S-N curves
- 7. Case Study 1: Box Beam of a Railway Wagon - 7.1 Introduction
- 7.2 Materials and methods
- 7.3 Results
- 7.4 Discussion and conclusions
- 8. Case Study 2: Hatch Corner Design for Container Ships - 8.1 Introduction
- 8.2 Materials and methods
- 8.3 Fatigue assessment
- 8.4 Conclusion
- References
- Appendix 1: Symbols
- Appendix 2: A2.4 References - A2.1 Need for enhanced accuracy
- A2.2 Alternative procedures for enhanced accuracy
- A2.3 Quadratic extrapolation
- Appendix 3: References
- Appendix 4: Hot Spot S-N Curves for Welded Aluminium Components