A round-robin study has been carried out within a national project in Sweden with the addition of an international participant, where several industrial partners and universities are participating. The project aims to identify variation and sources of variation in welding production, map scatter in fatigue life estimation, and define and develop concepts to reduce these, in all steps of product development. The participating organisations were asked to carry out fatigue life assessment of welded box structures, which is a component in load-carrying structures. The estimations of fatigue life have also been compared with fatigue test results. Detailed drawings, loads and material data were also given to the participants. The participants were supposed to use assessment methods based on global and local stresses using the design codes or recommendations they currently use in-house. Differences were identified between both methods and participants using the same codes/recommendations. Applicability and conditions from the cases in the codes were also identified to be differently evaluated between the participants. It could be concluded that for the applied cases the nominal stress method often overestimated the fatigue life and had a high scatter in the estimations by different participants. The effective notch method is conservative in comparison to the life of tested components with little scatter between the results derived by the participants. 

An analytical model for the fatigue probability of abrasive waterjet cut high strength steel as a function of surface roughness, surface residual stress, tensile strength and number of cycles to failure is presented. Based on the model, which is valid in the finite and infinite-life high cycle fatigue regime, the influence of the aforementioned parameters on the fatigue strength at different probability levels is studied. For validation, fatigue tests are performed on abrasive waterjet-cut dog-bone specimens manufactured from high-strength steel with a yield strength of 700 MPa. Residual stresses are measured parallel to the loading direction at the inlet, middle and outlet of the cut surface. Surface roughnesses are measured with laser line triangulation as well as a traditional contact stylus method, showing good agreement between both measurement techniques. The proposed probabilistic model shows good agreement with the experimental results with less than 4% error in the predicted mean fatigue limit. Furthermore, the applicability of the presented analytical expression in a probabilistic design framework is demonstrated. An engineering example is introduced demonstrating the implementation of the model in a finite-element simulation, accounting for both multiaxial loading and the statistical size effect. (c) 2021 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/).

In the current study a method to determine the location of fracture initiation for non-load carrying fillet welds based on continuous geometry measurements is proposed. Measurements and weld quality evaluation were carried out on welded specimens using the Winteria® software qWeld. One hundred nineteen specimens were produced, scanned, and fatigue tested until failure. The fracture surfaces have been investigated in order to find the location(s) for most probable point(s) of initiation. These data were then used to fit the proposed model parameters used to predict the point of initiation. Local weld geometry measurements were extracted from the predicted fracture initiation location(s) to analyse the correlation between local weld geometry and fatigue life. It was observed that fatigue life and leg length were positively correlated and that strong correlations exist between the individual geometrical parameters with regard to location of the fatigue crack initiation.

Digital weld quality assurance systems are increasingly used to capture local geometrical variations that can be detrimental for the fatigue strength of welded components. In this study, a method is proposed to determine the required scanning sampling resolution for proper fatigue assessment. Based on FE analysis of laser‐scanned welded joints, fatigue failure probabilities are computed using a Weakest‐link fatigue model with experimentally determined parameters. By down‐sampling of the scanning data in the FE simulations, it is shown that the uncertainty and error in the fatigue failure probability prediction increases with decreased sampling resolution. The required sampling resolution is thereafter determined by setting an allowable error in the predicted failure probability. A sampling resolution of 200 to 250 μm has been shown to be adequate for the fatigue‐loaded welded joints investigated in the current study. The resolution requirements can be directly incorporated in production for continuous quality assurance of welded structures. The proposed probabilistic model used to derive the resolution requirement accurately captures the experimental fatigue strength distribution, with a correlation coefficient of 0.9 between model and experimental failure probabilities. This work therefore brings novelty by deriving sampling resolution requirements based on the influence of stochastic topographical variations on the fatigue strength distribution. 

Progress in developing digital quality assurance systems for welded joints has made it possible to accurately measure the local geometry and its variation, making it possible to derive new relations between the geometric variations and fatigue. A probabilistic model for the fatigue strength is here presented based on the actual weld geometry. The novelty lies in that representative stresses can be determined for both the complete weld and sections of the weld. Calibration of the model using 105 fatigue-tested specimens shows a reduced variation in SN-diagrams compared with the nominal stress methods when substantial weld geometry variations are present.

Safe design against unstable fractures in load-bearing structures is crucial at sub-zero temperatures where the brittle fracture toughness can be unfavourable, especially for high-stress designs incorporating ultra-high-strength steels. The brittle fracture toughness of surface cracks in structural steel with a minimum yield strength of 1300 MPa is, for this reason, tested in the present study at sub-zero temperatures. The realistic flaws are compared with single-edge notched specimens (SEN(B)) from thicker plates with the same chemical composition, using a representative fracture toughness for a three-dimensional crack front according to the Master Curve method. A novel approach determines the latter without considering the local temperature and constraint variation through empirical relations. The experimental result shows a difference in the reference temperature between the two specimen types, which likely is the natural variation of the manufactured materials and/or a loss of constraint due to the difference in the scaled specimen deformation level.