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Article:Maggiolini, E., Tovo, R., Susmel, L. et al. ReuseUnless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version -refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher's website. TakedownIf you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request . 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 AbstractThis paper reports part of the work done in a research project aimed at developing an optimised process to join 38 mm diameter tubes of 6082-T6 aluminium alloy using friction stir welding (FSW), and then to determine the fatigue performance under tension, torsion and tensiontorsion loading conditions. The final outcome of the project is intended to be guidance for fatigue design of small diameter aluminium tubes joined by FSW, and this paper presents information on crack path and defects under the various loading conditions. Crack path analysis was performed using both low magnification stereo microscopy and scanning electron microscopy, in order to identify crack initiation sites, the direction of crack propagation and the interrelated influence of microstructure and weld geometry on the crack initiation path. KeywordsFriction stir welding; multiaxial fatigue; tension-torsion; 6082-T6 aluminium; small diameter tube; crack path. IntroductionWelding is the most common joining process in structural design and general manufacturing, and is statistically reliable provided that joint design adheres to codified guidelines.Nonetheless, cracking problems are often observed to be associated with the weld zone, arising from microstructural changes due to the weld thermal cycle, residual stresses induced by differential heating and cooling, and defects introduced in the weld zone either by local geometry changes (stress concentration points) or from the welding process (particularly in fusion welding, which is a casting process). Hence a major challenge faced in fatigue design is Whilst it is easy to join flat plate with FSW, it can be difficult to extend its applications to include tubes, in particular small diameter tubes, and other complex geometries. Friction stir welding of tubes has particular challenges in terms of pin plunge depth and support for the material during welding and also in terms of ...

This paper investigates two possible definitions of a non‐local effective stress: the weighted average value and the implicit gradient solution. These definitions are usually applied for strength assessment, particularly in the high cycle fatigue regime, in the presence of notches, defects, cracks or welded joint toes or roots. The present research analyses their general relationship in plane notches. Then, the paper presents a numerical method for their assessment by means of a general FE tool. Different solutions are calculated and compared by evaluating the results obtained from different finite element method commercial software.

Appropriate S‐N fatigue design curves for friction stir welded joints in aluminium alloys are currently not specified in design codes and standards. The present paper is intended to assist in enabling standardised fatigue design for such joints, through a comprehensive statistical analysis of more than 500 individual sets of data gathered from published literature. These data are used to establish the usual design fatigue curves for welds that give a 97.7% survival probability with 95% confidence. Experimental fatigue data represent defect‐free butt joints and include both flat plate and tubular joints between similar aluminium alloys (across the range of 2xxx, 5xxx, 6xxx, and 7xxx series). Weld conditions include as‐welded, machined, and postweld heat treated under constant amplitude cyclic loading at various stress ratios in the range from R = −1 to 0.5. A systematic comparison is presented by categorising the data according to the alloy type, temper condition, postweld heat treatment, and stress ratio and the correlation with the S‐N design curves from Eurocode 9 is also considered. The fatigue curves presented in this paper will serve as a useful guideline for engineers involved in design of friction stir aluminium joints subjected to in‐service fatigue loading.

The present paper investigates the accuracy of the Modified Wöhler Curve Method (MWCM) in estimating multiaxial fatigue strength of aluminium friction stir (FS) welded joints. Having developed a bespoke joining technology, circumferentially FS welded tubular specimens of Al 6082-T6 were tested under proportional and non-proportional tension and torsion, the effect of non-zero mean stresses being also investigated. The validation exercise carried out using the experimental results have demonstrated that the MWCM applied in terms of nominal stresses, notch stresses, and also the Point Method is accurate in predicting the fatigue lifetime of the tested FS welded joints, with its use resulting in life estimates that fall within the uniaxial and torsional calibration scatter bands