RESEARCH PAPER A robust stress analysis method for fatigue life prediction of welded structures Rakesh Goyal 1 & Mohamad El-Zein 2 & Grzegorz Glinka 3 Received: 17 August 2014 /Accepted: 5 January 2016 /Published online: 26 January 2016 # International Institute of Welding 2016 Abstract In the case of structural weldments, the procedure for estimating fatigue life requires information concerning ge- ometry of the object, loads, and material. Detailed knowledge of stress fields in the critical regions of weldments is used to determine the fatigue life. The main theme of the research discussed in this paper is to provide details of the methodolo- gy which has been developed to determine the peak stress and associated non-linear through-thickness stress distribution at the critical weld toe crack plane by using only the geometry- dependent stress concentration factors along with appropriate unique reference stress calculated in an efficient manner, e.g., without modeling geometrical weld toe details. The peak stress at the weld toe can be subsequently used for estimating the fatigue crack initiation life. The non-linear through-thick- ness stress distribution and the weight function method can be used for the determination of stress intensity factors and for the analysis of subsequent fatigue crack growth. Accurate peak stress estimation requires 3D fine mesh finite element (FE) models, accounting for the micro-geometrical features, such as the weld toe angle and weld toe radius. Such models are computationally expensive and therefore impractical. On the other hand, stresses at the sharp weld corners obtained from 3D coarse FE meshes are inaccurate and cannot be used directly for fatigue life estimations. This paper describes a robust, sufficiently accurate, and efficient stress analysis meth- od for fatigue life estimation of welded structures based on 3D FE coarse mesh models. Another objective is to establish a methodology which is capable of accounting for the actual variability of stress concentration factors at welds, welding defects such as misalignment, and incomplete penetration resulting from the manufacturing process. The methodology described in the paper has been validated by analyzing several weldments of varying geometrical and load configurations. The proposed methodology not only reduces conservative fa- tigue design of welded structures but also leads to significant savings concerning modeling and computation efforts. Keywords (IIW Thesaurus) Stress distribution . Weld toes . Prediction . Stress analysis . Fatigue life . Finite element analysis 1 Introduction Welding is one of the most widely used joining processes to manufacture machines and structures. In welded structures, the most obvious location of fatigue failure is either at the toe or root of the weld. It is very important to design welded structures in a way so that there is no premature fatigue failure of weld joints along with the universal requirement that design should be economical. Accurate fatigue life estimation of welded joints, at early design stage, is the key to achieve these contradictory requirements. The essential inputs required for any fatigue analysis are the geometry, load history, and mate- rial properties. A concise yet highly informative flow chart (Fig. 1) has been given by the SAE committee and is reproduced here, describing the information path for stress Recommended for publication by Commission XIII - Fatigue of Welded Components and Structures * Rakesh Goyal GoyalRakesh@JohnDeere.Com 1 John Deere India Private Limited, Pune, MH 411013, India 2 Moline Technology Innovation Center, Deere and Company, Moline, IL 61265, USA 3 Faculty of Engineering, University of Waterloo, Waterloo, Ontario, Canada Weld World (2016) 60:299–314 DOI 10.1007/s40194-016-0295-y